BEGIN:VCALENDAR
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METHOD:PUBLISH
X-WR-CALNAME;VALUE=TEXT:סמינרים | המחלקה למתמטיקה
PRODID:-//Drupal iCal API//EN
BEGIN:VEVENT
UID:calendar:3467:field_when:0:0
SUMMARY:On the PBW property for universal enveloping algebras
DTSTART:2023-03-29T07:30:00
DTEND:2023-03-29T08:30:00
DSCRIPTION:Speaker: Anton Khoroshkin (Haifa University)\n
Abstract:
The famous Poincaré-Birkhoff-Witt theorem states that there is a canonical filtration on the universal enveloping algebra of any Lie algebra such that the associated graded algebra is isomorphic to a symmetric algebra of the underlying space. I will explain what one can say about the PBW property for different algebraic structures, such as pre-Lie algebras, Poisson algebras, algebras admitting a pair of compatible Lie brackets, and many others.
Moreover, I will explain a necessary…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3468:field_when:0:1
SUMMARY:Derangements in permutation groups
DTSTART:2023-03-22T08:30:00
DTEND:2023-03-22T09:30:00
DSCRIPTION:Speaker: Daniele Garzoni (Tel Aviv University)\n
Abstract:
Given a group G acting on a set X, an element g of G is called a derangement if it acts without fixed points on X. The Boston--Shalev conjecture, proved by Fulman and Guralnick, asserts that in a finite simple group G acting transitively on X, the proportion of derangements is at least some absolute constant c > 0. We will first give an introduction to the subject, highlighting some connections with number theory. Then, we will see a version of this conjecture for the proportion of…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3466:field_when:0:2
SUMMARY:Hyperuniformity: unconventional ordering out of equilibrium
DTSTART:2023-03-16T10:45:00
DTEND:2023-03-16T11:45:00
DSCRIPTION:Speaker: Daniel Hexner (Technion)\n
Abstract:
The properties of materials are often understood in terms of their structure and symmetries.
Order is often manifested in correlations of an order parameter that extends throughout the system. In this talk I will discuss an exotic ordering that is paradoxically found in disordered systems. This ordering is known as hyperuniformity, and is defined as having suppressed fluctuations on arbitrary long length scales. While the fluctuations of a random uncorrelated arrangement of…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3464:field_when:0:3
SUMMARY:Club isomorphisms on higher Aronszajn trees, part 1
DTSTART:2023-02-09T12:00:00
DTEND:2023-02-09T14:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We will present the result of Krueger that assuming an ineffable cardinal it is consistent that CH holds and for any two normal countably closed $\omega_2$-Aronszajn trees are club-isomorphic.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3458:field_when:0:4
SUMMARY:Iterating the construction of inner models from extended logics, part 6
DTSTART:2023-01-26T12:00:00
DTEND:2023-01-26T14:00:00
DSCRIPTION:Speaker: Ur Ya'ar (BIU)\n
Abstract:
The last talk for this series
END:VEVENT
BEGIN:VEVENT
UID:calendar:3456:field_when:0:5
SUMMARY:Nodal count via topological persistence
DTSTART:2023-01-22T10:00:00
DTEND:2023-01-22T11:00:00
DSCRIPTION:Speaker: Lev Buhovski, TAU\n
Abstract:
It is possible to measure oscillations of a function by means of the theory of persistence modules and barcodes. I will explain how Sobolev norms can control such measurements. Applications include generalizations of Courant's nodal domain theorem and Bezout's theorem. The talk is based on a joint work with Jordan Payette, Iosif Polterovich, Leonid Polterovich, Egor Shelukhin, and Vukašin Stojisavljević. No prior knowledge of spectral geometry and topological persistence will be…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3457:field_when:0:6
SUMMARY:Iterating the construction of inner models from extended logics, part 5
DTSTART:2023-01-19T12:00:00
DTEND:2023-01-19T14:00:00
DSCRIPTION:Speaker: Ur Ya'ar (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3452:field_when:0:7
SUMMARY:Unstable orthogonal K-theory
DTSTART:2023-01-18T08:30:00
DTEND:2023-01-18T09:30:00
DSCRIPTION:Speaker: Andrei Lavrenov (Bar-Ilan University)\n
Abstract:
See attached file
END:VEVENT
BEGIN:VEVENT
UID:calendar:3454:field_when:0:8
SUMMARY:Classical Lie algebras at infinity
DTSTART:2023-01-15T10:00:00
DTEND:2023-01-15T11:00:00
DSCRIPTION:Speaker: Crystal Hoyt\n
Abstract:
In this talk, we will introduce infinite-dimensional Lie algebras which are direct limits of finite-dimensional Lie algebras, our main example being sl(infty). As time permits, we will discuss some recent motivation in modern mathematics for studying these Lie algebras.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3453:field_when:0:9
SUMMARY:Iterating the construction of inner models from extended logics, part 4
DTSTART:2023-01-12T12:00:00
DTEND:2023-01-12T14:00:00
DSCRIPTION:Speaker: Ur Ya'ar (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3448:field_when:0:10
SUMMARY:On Černy's conjecture
DTSTART:2023-01-11T08:30:00
DTEND:2023-01-11T09:30:00
DSCRIPTION:Speaker: Avraham Trakhtman (Bar-Ilan University)\n
Abstract:
A word w of letters on edges of the underlying graph of a deterministic
finite automaton (DFA) is called synchronizing if w sends all states of
the automaton to a unique state.
J. Černy discovered in 1964 a sequence of n-state complete DFA
possessing a minimal synchronizing word of length (n-1)^2.
The hypothesis, well known today as the Černy conjecture, formulated in 1966 by Starke, claims that the precise upper bound on the length of a synchronizing word for a complete DFA is…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3450:field_when:0:11
SUMMARY:Multi-Bubble Isoperimetric Problems - Old and New
DTSTART:2023-01-08T10:00:00
DTEND:2023-01-08T11:00:00
DSCRIPTION:Speaker: Emanuel Milman, Technion\n
Abstract:
The classical isoperimetric inequality in Euclidean space R^n states that among all sets (“bubbles”) of prescribed volume, the Euclidean ball minimizes surface area. One may similarly consider isoperimetric problems for more general metric-measure spaces, such as on the n-sphere S^n and on n-dimensional Gaussian space G^n (i.e. R^n endowed with the standard Gaussian measure). Furthermore, one may consider the “multi-bubble” isoperimetric problem, in which one prescribes the volume of …
END:VEVENT
BEGIN:VEVENT
UID:calendar:3451:field_when:0:12
SUMMARY:Iterating the construction of inner models from extended logics, part 3
DTSTART:2023-01-05T12:00:00
DTEND:2023-01-05T14:00:00
DSCRIPTION:Speaker: Ur Ya'ar (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3447:field_when:0:13
SUMMARY:Probabilistic laws on groups
DTSTART:2023-01-04T08:30:00
DTEND:2023-01-04T09:30:00
DSCRIPTION:Speaker: Guy Blachar (Bar-Ilan University)\n
Abstract:
Suppose a finite group satisfies the following property: If you take two random elements, then with probability bigger than 5/8 they commute. Then this group is commutative.
Starting from this well-known result, it is natural to ask: Do similar results hold for other laws (p-groups, nilpotent groups...)? Are there analogous results for infinite groups? Are there phenomena specific to the infinite setup?
We will survey known and new results in this area. New results are joint with…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3449:field_when:0:14
SUMMARY:Frobenius constants for families of elliptic curves
DTSTART:2023-01-01T10:00:00
DTEND:2023-01-01T11:00:00
DSCRIPTION:Speaker: Bidisha Roy, Scuola Normale Superiore di Pisa\n
Abstract:
Periods are complex numbers given as values of integrals of algebraic functions defined over domains, bounded by algebraic equations and inequalities with coefficients in Q. In this talk, we will deal with a class of periods, Frobenius constants, arising as matrix entries of the monodromy representations of certain geometric differential operators. More precisely, we will consider seven special Picard - Fuchs type second order linear differential operators corresponding to families…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3444:field_when:0:15
SUMMARY:Iterating the construction of inner models from extended logics, part 2
DTSTART:2022-12-29T12:00:00
DTEND:2022-12-29T14:00:00
DSCRIPTION:Speaker: Ur Ya'ar (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3446:field_when:0:16
SUMMARY:Overconvergence of étale (phi,Gamma)-modules in families
DTSTART:2022-12-28T08:00:00
DTEND:2022-12-28T09:00:00
DSCRIPTION:Speaker: Gal Porat (University of Chicago)\n
Abstract:
In recent years there has been growing interest in realizing the collection of Langlands parameters in various settings as a moduli space with a geometric structure. In particular, in the p-adic Langlands program, this space should come in two different forms of moduli spaces of (phi,Gamma)-modules: there is the Banach stack (also called the Emerton-Gee stack) and the analytic stack. In this talk, I will present a proof of a recent conjecture of Emerton, Gee, and Hellmann concerning…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3443:field_when:0:17
SUMMARY:First order problems of linear and Chevalley groups
DTSTART:2022-12-18T10:00:00
DTEND:2022-12-18T11:00:00
DSCRIPTION:Speaker: Helen Bunina\n
Abstract:
I will talk about elementary equivalence, elementary definability, regular bi-interpretability and universal equivalence of general linear groups and Chevalley groups over different classes of rings.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3442:field_when:0:18
SUMMARY:Growth, dynamics, and approximations of infinite-dimensional algebras
DTSTART:2022-12-14T08:30:00
DTEND:2022-12-14T09:30:00
DSCRIPTION:Speaker: Be'eri Greenfeld (University of California, San Diego)\n
Abstract:
The growth of an infinite-dimensional algebra is a fundamental tool to 'measure its infinitude'. Growth of algebras plays an important role in noncommutative geometry, representation theory, differential algebraic geometry, symbolic dynamics and various homological stability results in number theory and arithmetic geometry.
We analyze the space of growth functions of algebras, answering a question of Zelmanov on the existence of certain holes in this space. We then prove a strong…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3441:field_when:0:19
SUMMARY:The ICC property in Groups and Dynamics
DTSTART:2022-12-11T10:00:00
DTEND:2022-12-11T11:00:00
DSCRIPTION:Speaker: Joshua Frisch, École Normale Supérieure\n
Abstract:
A group is said to have the infinite conjugacy class (ICC) property if every non-identity element has an infinite conjugacy class. In this talk I will survey some ideas in geometric group theory, random walks and harmonic functions on groups, and topological dynamics and show how the ICC property sheds light on these three seemingly distinct areas. In particular I will discuss when a group has only constant bounded harmonic functions, when every proximal dynamical system has a fixed…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3437:field_when:0:20
SUMMARY:Iterating the construction of inner models from extended logics, part 1
DTSTART:2022-12-08T12:00:00
DTEND:2022-12-08T14:00:00
DSCRIPTION:Speaker: Ur Ya'ar (BIU)\n
Abstract:
One way of generalizing Goedel's constructible universe L, is to replace the notion of definability used at successor stage, and take all subsets of the last stage which are definable using a logic L* extending first order logic. This will result in a model of ZF, denoted C(L*). In some cases it will also be a model of AC. As in the case of L, we can formulate the axiom "V=C(L*)", but unlike L, it is not always the case that C(L*) |= "V=C(L*)", that is, when we construct C(L*) inside…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3439:field_when:0:21
SUMMARY:Cyclic diagrams and non-admissible irreducible representations of p-adic groups
DTSTART:2022-12-07T08:30:00
DTEND:2022-12-07T09:30:00
DSCRIPTION:Speaker: Mihir Sheth (Indian Institute of Science, Bangalore)\n
Abstract:
Let F be a non-archimedean local field of residue characteristic p. The smooth representation theory of GL_2(F) over characteristic p fields is qualitatively different from that over the fields of other characteristics. For example, over coefficient fields of characteristic p, a compact induction from a compact open subgroup can have infinitely many supercuspidal quotients (after fixing a central character). Further, there exist irreducible representations of GL_2(F) which are not…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3438:field_when:0:22
SUMMARY:Finite-dimensional algebras and their length
DTSTART:2022-12-04T10:00:00
DTEND:2022-12-04T11:00:00
DSCRIPTION:Speaker: Alexander Guterman\n
Abstract:
The length of a finite system of generators for a finite-dimensional (not necessarily associative) algebra over a field is the least positive integer k such that the products of length not exceeding k span this algebra as a vector space. The maximum length for the systems of generators of an algebra is called the length of this algebra. Length function is an important invariant widely used to study finite dimensional algebras since 1959. The length evaluation can be a difficult…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3440:field_when:0:23
SUMMARY:The Burnside problem for relatively small odd exponents
DTSTART:2022-11-30T08:30:00
DTEND:2022-11-30T09:30:00
DSCRIPTION:Speaker: Agatha Atkarskaya (Hebrew University of Jerusalem)\n
Abstract:
The Burnside problem asks if finitely generated groups with identity x^n = 1 are necessarily finite. In general, the answer is negative if the exponent n is large enough. The first negative solution for odd n at least 4381 was given by Novikov and Adian in 1968. Using different methods, this result was also proved by Olshanskii in 1982 for n > 10^10. The proof of Novikov and Adian is combinatorial, while the proof of Olshanskii is based on geometric considerations. We present a…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3436:field_when:0:24
SUMMARY:Rare events for stationary Gaussian functions
DTSTART:2022-11-27T10:00:00
DTEND:2022-11-27T11:00:00
DSCRIPTION:Speaker: Naomi Feldheim\n
Abstract:
A Gaussian stationary process is a random function f:R-->R whose distribution is invariant under real shifts, and whose evaluation at any finite number of points is a centered Gaussian random vector. The mathematical study of these random functions goes back at least 80 years, with pioneering works by Kac, Rice and Wiener. Nonetheless, many basic questions about them turned out to have complicated answers, or remained open for many years. One prominent example is estimating the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3435:field_when:0:25
SUMMARY:Sealing Kurepa Trees in ZFC
DTSTART:2022-11-24T12:00:00
DTEND:2022-11-24T14:00:00
DSCRIPTION:Speaker: Itamar Giron (HUJI)\n
Abstract:
A class of trees may be defined using shared properties: height, width, cardinality of the branch set, etc. For a tree T within a model M we ask if we may add a branch (or branches) to the model using some forcing notion without destroying said properties. If we cannot, we say the tree is sealed. A natural followup question is, under what conditions can we build a forcing notion which does not harm the properties of the tree, and seals it? In this lecture I show that given a Kurepa…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3433:field_when:0:26
SUMMARY:Artin's primitive root conjecture: classically and over Fq[T]
DTSTART:2022-11-20T10:00:00
DTEND:2022-11-20T11:00:00
DSCRIPTION:Speaker: Ezra Waxman, University of Haifa\n
Abstract:
In 1927, E. Artin proposed a conjecture for the natural density of primes p for which g is a primitive root mod p. By observing numerical deviations from Artin's originally predicted asymptotic, Derrick and Emma Lehmer (1957) identified the need for an additional correction factor; leading to a modified conjecture that was eventually proved correct by Hooley (1967), under the assumption of the Generalized Riemann Hypothesis (GRH). In this talk we discuss several variants of Artin's…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3434:field_when:0:27
SUMMARY:Partitions on topological spaces and a club-like principle, part 4
DTSTART:2022-11-17T10:00:02
DTEND:2022-11-17T10:04:00
DSCRIPTION:Speaker: Rodrigo Rey Carvalho (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3430:field_when:0:28
SUMMARY:Non-commutative Galois theory
DTSTART:2022-11-16T08:30:00
DTEND:2022-11-16T09:30:00
DSCRIPTION:Speaker: François Legrand (Université de Caën)\n
Abstract:
Inverse Galois theory, a topic initiated by Hilbert and Noether, is traditionally studied over fields. Yet Galois theory of fields has been generalized to division rings, by Bourbaki, Cartan, Jacobson, etc. In this talk, we will present several methods to produce Galois extensions of division rings with specified Galois groups.
================================================
https://us02web.zoom.us/j/87856132062
Meeting ID: 878 5613 2062
END:VEVENT
BEGIN:VEVENT
UID:calendar:3431:field_when:0:29
SUMMARY:New bounds on lattice covering volumes, and nearly uniform covers
DTSTART:2022-11-13T10:00:00
DTEND:2022-11-13T11:00:00
DSCRIPTION:Speaker: Barak Weiss, Tel Aviv University\n
Abstract:
Let L be a lattice in R^n and let K be a convex body. The covering volume of L with respect to K is the minimal volume of a dilate rK, such that L+rK = R^n, normalized by the covolume of L. Pairs (L,K) with small covering volume correspond to efficient coverings of space by translates of K, where the translates lie in a lattice. Finding upper bounds on the covering volume as the dimension n grows is a well studied problem, with connections to practical questions arising in computer…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3432:field_when:0:30
SUMMARY:Partitions on topological spaces and a club-like principle, part 3
DTSTART:2022-11-10T12:00:00
DTEND:2022-11-11T14:00:00
DSCRIPTION:Speaker: Rodrigo Rey Carvalho (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3429:field_when:0:31
SUMMARY:Some new constructions of supercuspidal mod p representations of GL_2(F), for a p-adic field F
DTSTART:2022-11-09T08:30:00
DTEND:2022-11-09T09:30:00
DSCRIPTION:Speaker: Michael Schein (Bar-Ilan University)\n
Abstract:
Let F / Q_p be a finite extension. In contrast to the situation for complex representations, very little is known about the irreducible supercuspidal mod p representations of GL_n(F), except in the case GL_2(Q_p). If F / Q_p is unramified and r is a generic irreducible two-dimensional mod p representation of the absolute Galois group of F, then nearly 15 years ago Breuil and Paskunas gave a beautiful construction of an infinite family of diagrams giving rise to supercuspidal mod p…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3428:field_when:0:32
SUMMARY:Hypoelliptic equations and geometry
DTSTART:2022-11-06T10:00:00
DTEND:2022-11-06T11:00:00
DSCRIPTION:Speaker: Nigel Higson, Penn State\n
Abstract:
In linear partial differential equations, hypoellipticity is the condition that if Df=g, with g smooth, then f is necessarily smooth too. The best-known hypoelliptic equations are the elliptic equations, which are characterized by an isotropy property that can be readily checked point-by-point. Various more general point-by-point sufficiency criteria for hypoellipticity have been studied, beginning with famous work of Lars Hormander in the 1960’s. Quite recently these criteria have…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3425:field_when:0:33
SUMMARY:Partitions on topological spaces and a club-like principle, part 2
DTSTART:2022-11-03T12:00:00
DTEND:2022-11-03T14:00:00
DSCRIPTION:Speaker: Rodrigo Rey Carvalho (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3424:field_when:0:34
SUMMARY:Convolutions of polynomial maps: a crossroads of algebra, geometry and analysis
DTSTART:2022-10-30T10:00:00
DTEND:2022-10-30T11:00:00
DSCRIPTION:Speaker: Yotam Hendel, Universite de Lille\n
Abstract:
Let f=(f_1,...,f_m) be a tuple of m polynomials with integer coefficients in n variables.
Then f can naturally be considered as a complex map f:C^n->C^m, and one may approach studying f from several different perspectives:
1) Arithmetic, by counting the number of solutions to the system of equations {f_i = c_i mod r}, for different choices of integers c_i and r.
2) Geometric, by studying the geometry and singularities of the fibers (level-sets) of the complex map f:C^n->C^m.
3…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3419:field_when:0:35
SUMMARY:Partitions on topological spaces and a club-like principle, part 1
DTSTART:2022-10-27T11:00:00
DTEND:2022-10-27T13:00:00
DSCRIPTION:Speaker: Rodrigo Rey Carvalho (BIU)\n
Abstract:
In this talk we explore some results from P. Komjáth and W. Weiss from the paper "Partitioning topological spaces in countably many pieces". First we address a problem found on a proof of a theorem, regarding the Cantor-Bendixson decomposition. Then we revisit an example from this paper made with $\diamondsuit$ and present a new example with the same purpose, but without the use of CH. For this we introduce the new principle $\clubsuit_{F}$. This talk will cover the contents of a…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3423:field_when:0:36
SUMMARY:On uniform number theoretic estimates for fibers of polynomial maps over finite rings of the form Z/p^kZ
DTSTART:2022-10-26T07:30:30
DTEND:2022-10-26T08:30:00
DSCRIPTION:Speaker: Yotam Hendel (Université de Lille)\n
Abstract:
Let f=(f_1,...,f_m) be an m-tuple of polynomials with integer coefficients in n variables. We study the number of solutions #{x:f(x)=y mod p^k} where y is an m-tuple of integers, and show that the geometry and singularities of the fibers of the map f:C^n->C^m determine the asymptotic behavior of this quantity as p, k and y vary.
In particular, we show that f:C^n->C^m is flat with fibers of rational singularities, a property abbreviated (FRS), if and only if #{x:f(x)=y mod p^k}/p…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3422:field_when:0:37
SUMMARY:The connection between ladder system uniformization and the Whitehead problem, part 4
DTSTART:2022-10-18T13:00:00
DTEND:2022-10-18T15:00:00
DSCRIPTION:Speaker: Márk Poór (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3418:field_when:0:38
SUMMARY:The connection between ladder system uniformization and the Whitehead problem, part 3
DTSTART:2022-10-06T13:00:00
DTEND:2022-10-06T15:00:00
DSCRIPTION:Speaker: Márk Poór (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3412:field_when:0:39
SUMMARY:The connection between ladder system uniformization and the Whitehead problem, part 2
DTSTART:2022-09-29T13:00:00
DTEND:2022-09-29T15:00:00
DSCRIPTION:Speaker: Márk Poór (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3411:field_when:0:40
SUMMARY:The connection between ladder system uniformization and the Whitehead problem, part 1
DTSTART:2022-09-22T13:00:00
DTEND:2022-09-22T15:00:00
DSCRIPTION:Speaker: Márk Poór (HUJI)\n
Abstract:
We give a brief overview on what had been already known, and present our new result asserting that (appropriate) uniformization principles grant not only the existence of almost free but non-free Whitehead groups, but imply that each strongly $\aleph_1$ abelian group of power $\aleph_1$ has the Whitehead property. This is joint work with S. Shelah (paper #486 in Shelah's list).
END:VEVENT
BEGIN:VEVENT
UID:calendar:3409:field_when:0:41
SUMMARY:A minimal Magidor-type forcing (countable case)
DTSTART:2022-09-08T13:00:00
DTEND:2022-09-08T15:00:00
DSCRIPTION:Speaker: Zhixing You (BIU)\n
Abstract:
In their paper from 2013, Koepke, Rasch and Schlicht defined a minimal Prikry-type forcing, which satisfies that any intermediate model is either the ground model or the generic extension.
In this talk, we try to generalize this result, and prove that for a countable limit ordinal delta, we can define a minimal Magidor-type forcing, which adds an increasing continuous sequence C_G of length delta such that any intermediate model between the ground model and the generic extension is…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3408:field_when:0:42
SUMMARY:On the delta-strongly compact cardinal, part 2
DTSTART:2022-09-01T13:00:00
DTEND:2022-09-01T15:00:00
DSCRIPTION:Speaker: Zhixing You (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3406:field_when:0:43
SUMMARY:Abelian quotient groups of finite groups
DTSTART:2022-08-28T09:00:00
DTEND:2022-08-28T10:00:00
DSCRIPTION:Speaker: George Glauberman (University of Chicago)\n
Abstract:
Suppose S is a non-identity Sylow p-subgroup of a finite group G and H is the normalizer of S in G. A classic theorem of Burnside asserts that if S is abelian, then G has a normal p-complement if and only if H has a normal p-complement. More generally, G has a normal subgroup with a quotient group of order p if and only if H has one; in this case, G is not a non-abelian simple group. There are analogous results in which p > 3, S is an arbitrary p-group, and H is replaced by the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3407:field_when:0:44
SUMMARY:On the delta-strongly compact cardinal, part 1
DTSTART:2022-08-25T13:00:00
DTEND:2022-08-25T15:00:00
DSCRIPTION:Speaker: Zhixing You (BIU)\n
Abstract:
Bagaria and Magidor introduced a weak version of strong compactness, δ-strong compactness, which characterizes some compactness properties successfully.
Besides, they also find that the least δ-strongly compact cardinal has odd properties. For example, the least δ-strongly compact cardinal may be singular, which separates δ-strong compactness from strong compactness.
In this series of talk, we will explore some basic properties of δ-strongly compact cardinals, and identity crisis…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3404:field_when:0:45
SUMMARY:Collapsing successors of singular cardinals using a theorem of Magidor
DTSTART:2022-08-18T13:00:00
DTEND:2022-08-18T15:00:00
DSCRIPTION:Speaker: Inber Oren (BGU)\n
Abstract:
In their paper [1] Adolf, Apter and Koepke showed that by assuming enough super-compactness for kappa one can prove that Aleph_{w1 + 1} can be collapsed to have cofinality w1 while preserving Aleph_{w1} and all cardinals above Aleph_{w1 + 1}. For this, they use Magidor's work [2] to get the required two-stage forcing.
The main goal of the lecture is to address the following natural question: When does this forcing preserve cardinals below kappa? We shall prove that no new bounded…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3403:field_when:0:46
SUMMARY:Forcing with matrices of countable elementary submodels
DTSTART:2022-08-09T08:00:00
DTEND:2022-08-09T10:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We present a forcing poset by Kuzeljevic and Todorcevic {https://www.ams.org/journals/proc/2017-145-05/S0002-9939-2017-13133-5/home.html}.
The conditions are finite matrices whose rows consist of isomorphic countable elementary submodels of a given structure of the form H_theta.
We will show that this forcing poset adds a Kurepa tree.
Moreover, forcing with a "continuous" modification adds an almost Souslin Kurepa tree, i.e., the level set of any antichain in the tree is not…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3400:field_when:0:47
SUMMARY:Weak Kurepa trees, slender tree properties, and guessing models, part 3
DTSTART:2022-08-02T08:00:00
DTEND:2022-08-02T10:00:00
DSCRIPTION:Speaker: Sarka Stejskalova (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3399:field_when:0:48
SUMMARY:Weak Kurepa trees, slender tree properties, and guessing models, part 2
DTSTART:2022-07-31T12:00:00
DTEND:2022-07-31T14:00:00
DSCRIPTION:Speaker: Sarka Stejskalova (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3397:field_when:0:49
SUMMARY:Matrix majorizations and their applications
DTSTART:2022-07-27T07:30:00
DTEND:2022-07-27T08:30:00
DSCRIPTION:Speaker: Pavel Shteyner\n
Abstract:
The notion of a vector majorization arose independently in a variety of contexts in the early 20th century. These contexts are Muirhead’s inequality, economical contexts (the Lorenz curve and Dalton principle), linear algebra (Schur’s work on the Hadamard inequality), and many others. There are several ways to extend the notion of vector majorizations to matrices. Different types of matrix majorizations have been motivated by different applications in the theory of statistical…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3396:field_when:0:50
SUMMARY:Weak Kurepa trees, slender tree properties, and guessing models, part 1
DTSTART:2022-07-24T12:00:03
DTEND:2022-07-24T14:00:00
DSCRIPTION:Speaker: Sarka Stejskalova (BIU)\n
Abstract:
The weak Kurepa hypothesis at omega_1 says that there exists a tree of size and height omega_1 which has at least omega_2 many cofinal branches. In the talk we will focus on the negation of the weak Kurepa hypothesis and the connection to the slender tree and ineffable slender tree properties at omega_2.
In the first part of the talk(s) we will focus on the negation of the weak Kurepa hypothesis and its effect on cardinal arithmetic. In the second part of the talk(s) we define the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3380:field_when:0:51
SUMMARY:An Aronszajn line with no countryman suborders
DTSTART:2022-06-23T11:00:00
DTEND:2022-06-23T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
Moore proved it is consistent assuming the existence of a supercompact cardinal that the class of uncountable linear orders has a five element basis.
The elements are X, w1, the dual of w1, C, and the dual of C, where X is any suborder of the reals of size w1, and C is any Countryman line.
This raises the question of the existence of an Aronszajn line with no countryman suborder, we will present such a construction by Moore from the combinatorial principle Mho.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3365:field_when:0:52
SUMMARY:Isogenous (non-)hyperelliptic CM Jacobians: constructions, results, and Shimura class groups
DTSTART:2022-06-22T07:30:00
DTEND:2022-06-22T08:30:00
DSCRIPTION:Speaker: Bogdan Dina (Hebrew University of Jerusalem)\n
Abstract:
Jacobians of CM curves are abelian varieties with a particularly large endomorphism algebra, which provides them with a rich arithmetic structure. The motivating question for the results in this talk is whether we can find hyperelliptic and non-hyperelliptic curves with maximal CM by a given order whose Jacobians are isogenous.
Joint work with Sorina Ionica, and Jeroen Sijsling considers this question in genus 3 by using the catalogue of CM fields in the LMFDB, and found a (small)…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3377:field_when:0:53
SUMMARY:Ideal growth in nilpotent rings and zeta functions of quiver representations
DTSTART:2022-06-19T11:00:00
DTEND:2022-06-19T12:30:00
DSCRIPTION:Speaker: Tomer Bauer (Bar-Ilan University)\n
Abstract:
In a seminal paper, Grunewald, Segal and Smith (1988) introduced zeta functions of groups and rings, enumerating various types of sub-objects, such as subgroups or two-sided ideals of finite index. Computations of these functions involve other enumeration problems in algebra and combinatorics.
Our main focus will be on zeta functions enumerating ideals of finite (additive) index, in nilpotent rings of class 2. It is well known that in this case there is a decomposition into an Euler…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3376:field_when:0:54
SUMMARY:Cyclic descents for permutations and tableaux
DTSTART:2022-06-19T09:00:00
DTEND:2022-06-19T10:00:00
DSCRIPTION:Speaker: Ron Adin, BIU\n
Abstract:
The study of descents of permutations may be traced back to Euler, and is fundamental to contemporary algebraic combinatorics and its applications. A cyclic extension of this notion was introduced in the late 20th century.
The talk will focus on aspects of descents and cyclic descents for permutations and for standard Young tableaux. Following an axiomatization of the notion of a cyclic descent extension, we will characterize sets of combinatorial objects for which such an…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3372:field_when:0:55
SUMMARY:From Sierpinski-type colourings to Ulam-type matrices
DTSTART:2022-06-16T14:00:00
DTEND:2022-06-16T15:30:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
Ulam matrices were introduced by Ulam in his study of the measure problem. Ulam’s construction applies to all successor cardinals Kappa, and later Hajnal extended the construction to apply to some limit cardinals as well. In my talk I will show how a colouring principle introduced by Sierpinski can be used to construct matrices with similar applications as the matrices of Ulam and Hajnal. I will also show how such colouring principles can be obtained from the existence of a non-…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3370:field_when:0:56
SUMMARY:Computation of lattice isomorphisms and the integral matrix similarity problem
DTSTART:2022-06-15T07:30:00
DTEND:2022-06-15T08:30:00
DSCRIPTION:Speaker: Henri Johnston (University of Exeter)\n
Abstract:
Let A be a finite-dimensional algebra over a number field and let Lambda be an order in A. Under certain hypothesis on A, we give an efficient algorithm that given two Lambda-lattices X and Y, determines whether X and Y are isomorphic, and if so, computes an explicit isomorphism X -> Y. As an application, we give an algorithm for the following long-standing problem: given a positive integer n and two n x n integral matrices A and B, determine whether A and B are similar over Z, and…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3371:field_when:0:57
SUMMARY:On pattern-avoidance and symmetry
DTSTART:2022-06-12T11:10:00
DTEND:2022-06-12T12:30:00
DSCRIPTION:Speaker: Avichai Marmor (Bar-Ilan University)\n
Abstract:
For a set $\Pi$ of permutations (patterns) in $S_k$, consider the set of all permutations in $S_n$ that avoid all patterns in $\Pi$. An important problem in current algebraic combinatorics is to find pattern sets $\Pi$ such that the corresponding quasi-symmetric function is symmetric for all $n$. Recently, Bloom and Sagan proved that for any $k \ge 4$, the size of such $\Pi$ must be at least $3$ (with one exception), and asked for a general bound.
In this talk, we prove that the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3369:field_when:0:58
SUMMARY:Uniqueness properties in representation theory and their applications
DTSTART:2022-06-12T10:00:00
DTEND:2022-06-12T11:00:00
DSCRIPTION:Speaker: Eyal Kaplan, BIU\n
Abstract:
Uniqueness properties are ubiquitous in many fields of study.
I will discuss uniqueness in the context of representation theory, and attempt
to motivate and explain the study of local factors, based on uniqueness.
The talk is motivated by a recent collaboration with Aizenbud and Gourevitch.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3368:field_when:0:59
SUMMARY:A Galvin-Hajnal theorem for generalized cardinal characteristics, part 2
DTSTART:2022-06-09T11:00:00
DTEND:2022-06-09T13:00:00
DSCRIPTION:Speaker: Chris Lambie-Hanson (Czech Academy of Sciences)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3366:field_when:0:60
SUMMARY:\tau(G) = \tau(G_1)
DTSTART:2022-06-08T07:30:00
DTEND:2022-06-08T08:30:00
DSCRIPTION:Speaker: Rony Bitan (Afeka Tel Aviv College of Engineering and Bar-Ilan University)\n
Abstract:
Given a smooth, geometrically connected and projective curve C defined over a finite field k, let K=k(C) be the function field of rational functions on C. The Tamagawa number \tau(G) of a semisimple K-group G is defined as the covolume of the discrete group G(K) (embedded diagonally) in the adelic group G(A) with respect to the Tamagawa measure. The Weil conjecture, recently proved by Gaitsgory and Lurie, states that if G is simply-connected then \tau(G)=1.
Our aim is to prove,…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3364:field_when:0:61
SUMMARY:A Galvin-Hajnal theorem for generalized cardinal characteristics, part 1
DTSTART:2022-06-02T12:00:00
DTEND:2022-06-02T14:00:00
DSCRIPTION:Speaker: Chris Lambie-Hanson (Czech Academy of Sciences)\n
Abstract:
We prove that a variety of generalized cardinal characteristics, including meeting numbers, the reaping number, and the dominating number, satisfy an analogue of the Galvin-Hajnal theorem, and hence also of Silver's theorem, at singular cardinals of uncountable cofinality. In the first talk, we will introduce some fundamental PCF-theoretic facts due to Shelah and Jech that will be used in our proof, and in the second talk we will prove our generalized Galvin-Hajnal theorem.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3363:field_when:0:62
SUMMARY:Some questions about polytopes
DTSTART:2022-05-22T11:00:00
DTEND:2022-05-22T12:30:00
DSCRIPTION:Speaker: Daniel Kalmanovich (Bar-Ilan University)\n
Abstract:
Convex polytopes are among the most fundamental geometric objects, and have numerous applications ranging from art, through engineering, to applied mathematics and computer science.
In this talk we will consider several questions about polytopes, focusing on combinatorial and geometric aspects. In particular, we will mention questions about the realization spaces of polytopes, Voronoi's conjecture on parllelohedra, face numbers of cubical polytopes and the VC-dimension of polytopes.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3359:field_when:0:63
SUMMARY:Topological group actions by group automorphisms and Banach representations
DTSTART:2022-05-22T09:00:00
DTEND:2022-05-22T10:00:00
DSCRIPTION:Speaker: Michael Megrelishvili, BIU\n
Abstract:
To every Banach space V one may associate a continuous dual action of the topological group Iso(V)
of all linear isometries on the weak-star compact unit ball B* of the dual space V*.
Which actions G x X --> X are "subactions" of Iso(V) x B* --> B* for nice Banach spaces V ?
We study Banach representability for actions of topological groups on groups by automorphisms;
in particular, an action on itself by conjugations.
The natural question is to examine when we…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3358:field_when:0:64
SUMMARY:Ramsey degrees and topological partition theorems
DTSTART:2022-05-19T12:00:00
DTEND:2022-05-19T14:00:00
DSCRIPTION:Speaker: Jing Zhang (BIU)\n
Abstract:
We will go over the theorem of Todorcevic and Raghavan that any finite coloring on pairs from an aleph1 subset of the reals, we can find an almost monochromatic subset homeomorphic to the rationals.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3355:field_when:0:65
SUMMARY:The resolution of Kräuter's conjecture on the permanent, and beyond
DTSTART:2022-05-18T07:30:00
DTEND:2022-05-18T08:30:00
DSCRIPTION:Speaker: Alexander Guterman (Moscow State University, visiting the Weizmann Institute of Science)\n
Abstract:
The talk is based on joint works with Mikhail Budrevich and Constantine Taranin.
Two important functions in matrix theory, the determinant and the permanent, have similar definitions. However, while the determinant may be computed in polynomial time, it is an open question whether fast algorithms computing the permanent exist. Therefore, any bounds on the permanent are of interest.
The class of matrices with entries 1 and -1 is very important in algebra, combinatorics, and their…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3354:field_when:0:66
SUMMARY:Covering the edges of a complete geometric graph with convex polygons
DTSTART:2022-05-15T11:00:00
DTEND:2022-05-15T12:30:00
DSCRIPTION:Speaker: Oren Yerushalmi (Technion)\n
Abstract:
Given a set $P$ of $m \geq 3$ points in general position in the plane, we want to find the smallest possible number of convex polygons with vertices in $P$ such that the edges of all these polygons contain all the ${m \choose 2}$ straight line segments determined by the points of $P$.
We show that if $m$ is odd, the answer is $\frac{m^2-1}{8}$ regardless of the choice of $P$. The answer in the case where $m$ is even depends on the choice of $P$ and not only on $m$. Nearly tight…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3357:field_when:0:67
SUMMARY:Directions in graph rigidity
DTSTART:2022-05-15T09:00:00
DTEND:2022-05-15T10:00:00
DSCRIPTION:Speaker: Eran Nevo, HUJI\n
Abstract:
Given a graph G and an embedding of its vertices in R^d, what continuous motions of the vertices preserve all edge lengths?
Clearly all motions induced by an isometry of R^d do, these are the trivial motions; are there any others?
If the answer is NO for all (equivalently, for one) generic embedding, G is called d-rigid. What are the d-rigid graphs?
This problem has been extensively studied since the 70s, and is still widely open for d>=3.
It is studied mainly from algebraic…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3356:field_when:0:68
SUMMARY:Galvin's Problem In Higher Dimensions
DTSTART:2022-05-12T12:00:00
DTEND:2022-05-12T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
In 1970's Galvin conjectured that for all colorings of the reals there is a subset H of the reals homeomorphic to the rational numbers that gets at most two colors. i.e. the 2-dimensional Ramsey degree of the rational with respect to the reals is 2. Baumgartner proved that if we consider any infinite countable Hausdorff space X then there is a coloring with \omega many colors, which takes all its values on subsets homeomorphic to \mathbb{Q}. In paper from 2018 Raghavan and Todorcevic…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3353:field_when:0:69
SUMMARY:Zeta functions of quiver representations and their applications
DTSTART:2022-05-11T07:30:00
DTEND:2022-05-11T08:30:00
DSCRIPTION:Speaker: Seungjai Lee (Seoul National University)\n
Abstract:
We introduce and study multivariate zeta functions enumerating subrepresentations of integral quiver representations and discuss their connections to various enumeration problems in algebra. This is joint work with Christopher Voll.
================================================
https://us02web.zoom.us/j/87856132062
Meeting ID: 878 5613 2062
END:VEVENT
BEGIN:VEVENT
UID:calendar:3351:field_when:0:70
SUMMARY:Character formulas and descent representations for colored permutation groups
DTSTART:2022-05-08T11:00:00
DTEND:2022-05-08T12:30:00
DSCRIPTION:Speaker: Vassilis Moustakas (Bar-Ilan University)\n
Abstract:
The quasisymmetric generating function of an inverse descent class is known to be symmetric, and there is a corresponding descent representation of the symmetric group. This result was generalized to products of inverse descent classes and Schur-positive sets of permutations by Elizalde and Roichman (2017), and to signed permutations by Adin, Athanasiadis, Elizalde and Roichman (2017).
In this talk we present colored extensions of these two results. Proof ingredients include a new…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3352:field_when:0:71
SUMMARY:From discrete Fourier analysis to Cryptanalysis
DTSTART:2022-05-08T09:00:00
DTEND:2022-05-08T10:00:00
DSCRIPTION:Speaker: Nathan Keller, BIU\n
Abstract:
Discrete Fourier analysis studies functions on the discrete cube {-1,1}^n, using their discrete Fourier expansion and functional-analytic tools. Results in discrete Fourier analysis have applications in diverse fields, ranging from social choice and machine learning to mathematical physics. Cryptanalysis studies the practical security of the encryption schemes we use. The central object in cryptanalysis is "attack techniques" – which are algorithms that allow an adversary to…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3349:field_when:0:72
SUMMARY:Random packings and liquid crystals
DTSTART:2022-05-01T11:00:00
DTEND:2022-05-01T12:30:00
DSCRIPTION:Speaker: Ron Peled (Tel-Aviv University)\n
Abstract:
Let T be a subset of R^d, such as a ball, a cube or a cylinder, and consider all possibilities for packing translates of T, perhaps with its rotations, in some bounded domain in R^d. How does a typical packing of this sort look like? One mathematical formalization of this question is to fix the density of the packing and sample uniformly among all possible packings with this density. Discrete versions of the question may be formulated as choosing a random independent set in a suitable…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3350:field_when:0:73
SUMMARY:On the Fourier decay for self-similar measures
DTSTART:2022-05-01T09:00:00
DTEND:2022-05-01T10:00:00
DSCRIPTION:Speaker: Boris Solomyak, BIU\n
Abstract:
A finite positive measure on the Euclidean space is called Rajchman if its Fourier transform tends to zero at infinity.
Absolutely continuous measures are Rajchman by the Riemann-Lebesgue Lemma, but it is a delicate question to decide which singular measures are such.
For many purposes simple convergence if the Fourier transform to zero is not sufficient and some quantitative decay is needed.
Recently there has been renewed interest and a lot of activity in studying such…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3347:field_when:0:74
SUMMARY:Construction of id_p(C,I)-positive coloring
DTSTART:2022-04-28T14:30:00
DTEND:2022-04-28T17:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
For kappa Mahlo and a stationary subset of kappa that does not reflect at regulars, we follow Hoffman's proof to show that for Shelah's ideal id_p(C,I), there is a coloring c:[\kappa]^2\rightarrow\kappa such that, for every unbounded set A, c[[A]^2] is measure one with respect to id_p(C,I)
END:VEVENT
BEGIN:VEVENT
UID:calendar:3348:field_when:0:75
SUMMARY:Noncommutative inclusion-exclusion, partial representations of semigroups, and nonassociative Specht polynomials
DTSTART:2022-04-27T07:30:00
DTEND:2022-04-27T08:30:00
DSCRIPTION:Speaker: Uzi Vishne (Bar-Ilan University)\n
Abstract:
The dimension of the space of multilinear products of higher commutators is equal to the number of derangements, $[e^{-1}n!]$.
Our search for a combinatorial explanation for this fact led us to study representations of left regular bands, whose resolution is obtained through analysis of cubical partial representations. There are applications in combinatorics, probability, and nonassociative algebra.
This is joint work with Guy Blachar and Louis Rowen.
The lecture is dedicated to…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3346:field_when:0:76
SUMMARY:The BCFW triangulation of the amplituhedron
DTSTART:2022-04-24T11:30:00
DTEND:2022-04-24T13:00:00
DSCRIPTION:Speaker: Chaim Even-Zohar (Technion)\n
Abstract:
The amplituhedron A(n,k,m) is a geometric object, discovered by Arkani-Hamed and Trnka (2013) in the study of scattering amplitudes in quantum field theories. They conjectured that A(n,k,4) admits a decomposition based on a certain combinatorial structure. The components are images of BCFW positroid cells of the Grassmannian Gr(k,n), which arise from the Britto–Cachazo–Feng–Witten recurrence (2005).
In a recent paper with Tsviqa Lakrec and Ran Tessler, we prove this conjecture. …
END:VEVENT
BEGIN:VEVENT
UID:calendar:3344:field_when:0:77
SUMMARY:The beauty of ART: Thoma's theorem and other animals
DTSTART:2022-04-24T09:00:00
DTEND:2022-04-24T10:00:00
DSCRIPTION:Speaker: Natalia Tsilevich, St.Petersburg Dept. of Steklov Institute of Mathematics\n
Abstract:
I will survey the basic ideas and results of asymptotic representation
theory (ART), mostly of symmetric groups, and then focus on a recent
novel approach to Thoma's theorem based on the combinatorial
Robinson-Schensted-Knuth correspondence, as well as other recent
contributions.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3335:field_when:0:78
SUMMARY:High-girth Steiner triple systems
DTSTART:2022-04-10T11:00:00
DTEND:2022-04-10T12:30:00
DSCRIPTION:Speaker: Michael Simkin (Harvard)\n
Abstract:
We prove a 1973 conjecture of Erdős on the existence of Steiner triple systems with arbitrarily high girth. (The girth of an STS is the smallest g>3 for which there exist g vertices spanning at least g-2 triangles.) Our construction builds on the methods of iterative absorption (Glock, Kühn, Lo, and Osthus) and the high-girth triangle removal process (Glock, Kühn, Lo, and Osthus and independently Bohman and Warnke). In particular, we extend iterative absorption to handle triangle-…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3334:field_when:0:79
SUMMARY:Some new parallels between groups and Lie algebras, or What can be simpler than a multiplication table?
DTSTART:2022-04-09T21:00:00
DTEND:2022-04-10T20:04:04
DSCRIPTION:Speaker: Boris Kunyavskii (BIU)\n
Abstract:
We give a survey of recent developments in the study of equations in groups and Lie algebras and related local-global invariants, focusing on parallels between the two algebraic structures.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3337:field_when:0:80
SUMMARY:On weak and middle diamonds, part 2
DTSTART:2022-04-07T14:30:00
DTEND:2022-04-07T17:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3333:field_when:0:81
SUMMARY:The structure of axial algebras
DTSTART:2022-04-06T07:30:00
DTEND:2022-04-06T08:30:00
DSCRIPTION:Speaker: Louis Rowen (Bar-Ilan University)\n
Abstract:
Joint work with Yoav Segev.
``Fusion rules'' are laws of multiplication among eigenspaces of an idempotent. This terminology is relatively new and is closely related to axial algebras, introduced recently by Hall, Rehren and Shpectorov, defined as nonassociative algebras generated by semisimple idempotents of degree 3, satisfying fusion rules based on a natural 2-grading . Axial algebras, in turn, are closely related to 3-transposition groups and vertex operator algebras.
We introduce…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3330:field_when:0:82
SUMMARY:Leray numbers of tolerance complexes
DTSTART:2022-04-03T11:00:00
DTEND:2022-04-03T12:30:00
DSCRIPTION:Speaker: Alan Lew (Hebrew University of Jerusalem)\n
Abstract:
In this talk we will discuss the Leray and collapsibility numbers of a simplicial complex K, and their role in Helly-type theorems in combinatorial geometry. The Leray number is, roughly speaking, the hereditary homological dimension of K, while the collapsibility number captures the complexity of dismantling K by sequentially removing free faces from K.
Following the formal definition of these parameters and their connection to the combinatorics of convex sets, we will introduce the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3332:field_when:0:83
SUMMARY:Multiplicities in relative representation theory
DTSTART:2022-04-03T09:00:00
DTEND:2022-04-03T10:00:00
DSCRIPTION:Speaker: Avraham Aizenbud, Weizmann Institute\n
Abstract:
The study of multiplicities is a central question in abstract harmonic analysis. I will present this question in various settings, and introduce a central conjecture about the boundedness of multiplicities. If time allows, I will present several recent results regarding this conjecture.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3331:field_when:0:84
SUMMARY:On weak and middle diamonds, part 1
DTSTART:2022-03-31T14:30:00
DTEND:2022-03-31T17:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
We'll survey some classical works on weak diamond and more recent works on middle diamond
END:VEVENT
BEGIN:VEVENT
UID:calendar:3327:field_when:0:85
SUMMARY:Ramanujan-style congruences for prime level
DTSTART:2022-03-30T07:30:00
DTEND:2022-03-30T08:30:00
DSCRIPTION:Speaker: Moni Kumari (Bar-Ilan University)\n
Abstract:
Ramanujan in 1916 proved the following notable congruence
$$\tau(n)\equiv \sigma_{11}(n) \pmod{691}, \forall~ n\ge 1$$
between the two important arithmetic functions $\tau(n)$ and $\sigma_{11}(n)$. In other words, this says that there is a congruence between the cuspidal Hekce eigenform $\Delta(z)$ and the non-cuspidal eigenform $E_{12}(z)$ modulo the prime $691$. Existence of such congruences opened the door for many modern developments in the theory of modular forms.
There…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3328:field_when:0:86
SUMMARY:Measures induced by words on GL_n(q) and free group algebras
DTSTART:2022-03-27T11:00:00
DTEND:2022-03-27T12:30:00
DSCRIPTION:Speaker: Danielle West (Tel-Aviv University)\n
Abstract:
Fix a finite field K and a word w in a free group F. A w-random element in GL_n(K) is obtained by substituting the letters of w with uniform random elements of GL_n(K). For example, if w = abab^{-2}, a w-random element is ghgh^{-2} with g,h independent and uniformly random in GL_n(K). The moments of w-random elements reveal a surprising structure which relates to the free group algebra K[F].
In this talk I will describe what we know about this structure, and draw some analogies to w…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3329:field_when:0:87
SUMMARY:Rates of growth in hyperbolic (and other) groups
DTSTART:2022-03-27T09:00:00
DTEND:2022-03-27T10:00:00
DSCRIPTION:Speaker: Zlil Sela, HUJI\n
Abstract:
In the late 1970s W. Thurston proved that the countable set of volumes of
closed hyperbolic 3-manifolds is well-ordered, that only finitely many closed hyperbolic
3-manifolds can have the same volume, and that the ordinal of the set of these volumes is
${\omega_0}^{\omega_0}$.
We prove analogous results for the rates of growth of hyperbolic (and other) groups.
We study the countable set of rates of growth of a hyperbolic group with respect to all
its finite sets of generators…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3325:field_when:0:88
SUMMARY:On grids corresponding to number fields, their distribution, and a generalized Weyl theorem
DTSTART:2022-03-23T08:30:00
DTEND:2022-03-23T09:30:00
DSCRIPTION:Speaker: Yuval Yifrach (Technion)\n
Abstract:
It was shown by M. Bhargava and P. Harron that for n=3,4,5, the shapes of rings of integers of S_n-number fields of degree n become equidistributed in a certain homogeneous space when the fields are ordered by absolute discriminant. We present a family of analogous distribution questions in some family of torus bundles over the aforementioned homogeneous space and discuss their answers. Our main tool is a new high dimensional equidistribution result in the flavor of Weyl's…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3319:field_when:0:89
SUMMARY:Nearly special free Souslin tree
DTSTART:2022-03-21T10:00:00
DTEND:2022-03-21T12:00:00
DSCRIPTION:Speaker: Shira Greenstein (BIU)\n
Abstract:
For an infinite cardinal lambda and a cardinal chi > 1 such that lambda^{<chi}=lambda, assuming an instance of the proxy principle at lambda^+, we construct a chi-free lambda^+-Souslin tree whose chi power is special.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3320:field_when:0:90
SUMMARY:On convex holes in d-dimensional point sets
DTSTART:2022-03-20T12:00:00
DTEND:2022-03-20T13:30:00
DSCRIPTION:Speaker: Ron Holzman (Technion)\n
Abstract:
Given a finite set $P \subseteq \mathbb{R}^d$, points $a_1, a_2, \dots, a_{\ell} \in P$ form an $\ell$-hole in $P$ if they are the vertices of a convex polytope which contains no points of $P$ in its interior.
We construct arbitrarily large point sets in general position in $\mathbb{R}^d$ having no holes of size $2^{7d}$ or more. This improves the previously known upper bound of order $d^{d+o(d)}$ due to Valtr. Our construction uses a certain type of designs, originating from…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3326:field_when:0:91
SUMMARY:On the Fourier decay for self-similar measures
DTSTART:2022-03-19T22:00:00
DTEND:2022-03-20T11:00:30
DSCRIPTION:Speaker: Boris Solomyak (BIU)\n
Abstract:
A finite positive measure on the Euclidean space is called Rajchman if its Fourier transform tends to zero at infinity.
Absolutely continuous measures are Rajchman by the Riemann-Lebesgue Lemma, but it is a delicate question to decide which singular measures are such.
For many purposes simple convergence if the Fourier transform to zero is not sufficient and some quantitative decay is needed.
Recently there has been renewed interest and a lot of activity in studying such…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3317:field_when:0:92
SUMMARY:Arc-intersection queries amid triangles in three dimensions and related problems
DTSTART:2022-03-13T12:00:00
DTEND:2022-03-13T13:30:00
DSCRIPTION:Speaker: Esther Ezra (Bar-Ilan University)\n
Abstract:
Let T be a set of n triangles in 3-space, and let \Gamma be a family of algebraic arcs of constant complexity in 3-space. We show how to preprocess T into a data structure that supports various \emph{intersection queries} for query arcs \gamma \in \Gamma, such as detecting whether \gamma intersects any triangle of T, reporting all such triangles, counting the number of intersection points between \gamma and the triangles of T, or returning the first triangle intersected by a directed…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3318:field_when:0:93
SUMMARY:Marginalia to two theorems of Magidor
DTSTART:2022-03-13T10:00:00
DTEND:2022-03-13T11:00:00
DSCRIPTION:Speaker: Assaf Rinot, BIU\n
Abstract:
In a paper published at the Annals of Mathematics in 1977,
Magidor proved that it is consistent that the first cardinal at which
the generalized continuum hypothesis (GCH) fails be the very first
singular cardinal Aleph_w. This demonstrates the failure of a
compactness property for Aleph_w. In a paper from 1982, Magidor proved
that Aleph_w can satisfy yet another compactness property. It remained
open ever since whether the two results can coexist in the same model.
In this talk, I…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3316:field_when:0:94
SUMMARY:Combinatorial number theory with nonstandard methods
DTSTART:2022-03-10T15:30:00
DTEND:2022-03-10T18:00:00
DSCRIPTION:Speaker: Jing Zhang (BIU)\n
Abstract:
We will survey applications of nonstandard analysis to prove theorem in additive Ramsey theory and combinatorial number theory. We will use Jin's sumset theorem and the recent solution of the Erdos' sumset conjecture as illustrating examples.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3313:field_when:0:95
SUMMARY:Minimality of topological matrix groups and Fermat primes
DTSTART:2022-03-09T08:30:00
DTEND:2022-03-09T09:30:00
DSCRIPTION:Speaker: Meny Shlossberg (Reichman University)\n
Abstract:
Our aim is to study topological minimality of some natural matrix groups. We show that the special upper triangular group SUT(n, F) is minimal for every local field F of characteristic distinct from 2. This result is new even for the field R of reals and it leads to some important consequences. We prove criteria for the
minimality and total minimality of the special linear group SL(n, F), where F is a subfield of a local field. One of our main applications is a characterization of…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3315:field_when:0:96
SUMMARY:Affine representations, harmonic functions, and group boundaries
DTSTART:2022-03-06T10:00:00
DTEND:2022-03-06T11:00:00
DSCRIPTION:Speaker: Hillel Furstenberg, HUJI\n
Abstract:
If Q is a convex set, a transformation T: Q ->Q is affine if it preserves the convex structure of Q. An affine representation of a group is a homomorphism of G to the group of invertible affine transformations of a compact convex Q. It is irreducible if no proper closed, convex subset of Q is left invariant. Abelian and compact groups have no non-trivial irreducible affine representations. From the classical theory of harmonic functions we show that any bounded harmonic…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3312:field_when:0:97
SUMMARY:Growth of unbounded subsets in nilpotent groups, word statistics and random polygons
DTSTART:2022-03-02T08:30:30
DTEND:2022-03-02T09:30:00
DSCRIPTION:Speaker: Be'eri Greenfeld (University of California, San Diego)\n
Abstract:
Let $G$ be a group. Let $g(k,n)$ be the maximum number of length-n words over an arbitrary k-letter subset within $G$. How does $g(k,n)$ behave? Obviously $g(k,n)$ is at most $k^n$, and Semple-Shalev proved that if $G$ is finitely generated and residually finite then $g(k,n)<k^n$ (for some, and hence for all sufficiently large k,n) if and only if G is virtually nilpotent. In this case, it is natural to ask how far can g(k,n) be from $k^n$. For k fixed and n ending to infinity, $g(k…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3311:field_when:0:98
SUMMARY:Cofinal types on w1 and w2, part 10
DTSTART:2022-02-22T12:00:00
DTEND:2022-02-22T14:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3310:field_when:0:99
SUMMARY:Cofinal types on w1 and w2, part 9
DTSTART:2022-02-15T12:00:00
DTEND:2022-02-15T14:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3308:field_when:0:100
SUMMARY:Colouring orders and ordering trees
DTSTART:2022-02-08T10:00:00
DTEND:2022-02-08T12:00:00
DSCRIPTION:Speaker: Miguel Moreno (Vienna)\n
Abstract:
One of the main motivations of generalised descriptive set theory is to use the Borel reducibility to study the complexity of theories. Following that motivation, one of the main question is whether the isomorphism relation of any classifiable theory is Borel reducible to the isomorphism relation of any non-classifiable theory. This has been proved to be consistent and under certain cardinality assumptions, the isomorphism relation of any classifiable theory is Borel reducible to the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3307:field_when:0:101
SUMMARY:When Luzin met Souslin, part 2
DTSTART:2022-02-01T12:00:00
DTEND:2022-02-01T14:00:00
DSCRIPTION:Speaker: Assaf Rinot (BIU)\n
Abstract:
We continue with the derivation of club_AD from a Luzin set, and then point out how to also get the same conclusion from the stick principle.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3305:field_when:0:102
SUMMARY:When Luzin met Souslin, part 1
DTSTART:2022-01-25T12:00:00
DTEND:2022-01-25T14:00:00
DSCRIPTION:Speaker: Assaf Rinot (BIU)\n
Abstract:
In a previous joint work with Shalev, we introduced the guessing principle club_AD, proved that it follows from the existence of a Souslin tree, and that it is sufficient for the construction of a Dowker S-space, as well as an O-space. Here we show that the same principle follows from the existence of a Luzin set.
This is joint work with Roy Shalev.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3297:field_when:0:103
SUMMARY:The Polynomial Method
DTSTART:2022-01-10T14:40:00
DTEND:2022-01-10T15:30:00
DSCRIPTION:Speaker: Noga Alon\n
Abstract:
A basic result in Algebraic Geometry implies that a nonzero multivariate polynomial of low degree cannot vanish over a large box. This can be used to obtain results in extremal combinatorics, graph theory, additive number theory and combinatorial geometry.
I will describe recent and less recent applications of the technique, and will mention several intriguing open problems.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3292:field_when:0:104
SUMMARY:Twisted cyclic homology and crossed product algebras
DTSTART:2022-01-05T08:30:00
DTEND:2022-01-05T09:30:00
DSCRIPTION:Speaker: Jack Shapiro (Washington University in St. Louis)\n
Abstract:
See abstract in the attached pdf file.
==================================
https://us02web.zoom.us/j/87856132062
Meeting ID: 878 5613 2062
END:VEVENT
BEGIN:VEVENT
UID:calendar:3301:field_when:0:105
SUMMARY:עיון מחודש בשיטת רבי אהרן בן מאיר בקביעת השנים ד'תרפ"ב-ד'תרפ"ד: הצעת פתרון לשאלת סיבת המחלוקת.
DTSTART:2022-01-04T15:45:00
DTEND:2022-01-04T16:30:00
DSCRIPTION:Speaker: ד"ר שי ואלטר ומר יוסף יצחק רוטנברג\n
Abstract:
סיבת מחלוקת קביעת הלוח בין ר' אהרן בן מאיר ובין בני בבל בשנים ד'תרפ"ב-תרפ"ד נותרה בגדר שאלה מסקרנת וחוקרים הציעו מספר הסברים לפתור את התעלומה. בהרצאה זאת נסקור בקצרה חלק מהפתרונות שהוצעו, ולבסוף ניטען כי יש קשר אפשרי בין מחלוקת זאת לתכניו של מכתב ראש הגולה על קביעת שנת ד'תקצ"ו. בתוך דברינו נתייחס בהעמקה לתפקידו של כלל דחיית "מולד זקן" בלוח העברי.
להרצאה המצולמת
END:VEVENT
BEGIN:VEVENT
UID:calendar:3294:field_when:0:106
SUMMARY:Site percolation on pseudo-random graphs
DTSTART:2022-01-02T12:00:00
DTEND:2022-01-02T13:30:00
DSCRIPTION:Speaker: Sahar Diskin, Tel Aviv University\n
Abstract:
In the site percolation model, a random induced subgraph G[R] of a given graph G is formed by putting every vertex v of G into a random subset R with probability p and independently. One then researches typical properties of G[R], like the sizes of its connected components.
Here we study site percolation on pseudo-random graphs, specifically on (n,d,\lambda)-graphs, which are d-regular graphs on n vertices with all eigenvalues but the first (trivial) one bounded in absolute values…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3295:field_when:0:107
SUMMARY:Forcing-theoretic approach to universal homogeneous structures, part 5
DTSTART:2021-12-28T12:00:00
DTEND:2022-01-28T14:00:00
DSCRIPTION:Speaker: Ziemek Kostana (BIU)\n
Abstract:
This is the last lecture for this series
END:VEVENT
BEGIN:VEVENT
UID:calendar:3293:field_when:0:108
SUMMARY:Combinatorial actions and Gelfand property in affine Weyl groups
DTSTART:2021-12-26T12:05:00
DTEND:2021-12-26T13:30:00
DSCRIPTION:Speaker: Pál Hegedűs (Rényi Institute)\n
Abstract:
The affine Weyl group G of type C has many natural actions on finite
combinatorial objects (for example on the so called "arc permutations").
Their common feature is an action of the finite Weyl group of type C and
a "rotation", a one dimensional linear action of the translation
subgroup. The action of the finite Weyl group is multiplicity-free, so a
natural question arose, whether the original action is also
multiplicity-free? It turns out that it is not, but it is "almost," that…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3290:field_when:0:109
SUMMARY:On the symbol length of symbols in Galois cohomology
DTSTART:2021-12-22T08:30:00
DTEND:2021-12-22T09:30:00
DSCRIPTION:Speaker: Eliyahu Matzri (Bar-Ilan University)\n
Abstract:
Let $F$ be a field with absolute Galois group $G_F$, $p$ be a prime, and $\mu_{p^e}$ be the $G_F$-module of roots of unity of order dividing $p^e$ in a fixed algebraic closure of $F$.
Let $\alpha \in H^n(F,\mu_{p^e}^{\otimes n})$ be a symbol (i.e $\alpha=a_1\cup \dots \cup a_n$ where $a_i\in H^1(F, \mu_{p^e})$) with effective exponent $p^{e-1}$ (that is $p^{e-1}\alpha=0 \in H^n(G_F,\mu_p^{\otimes n})$. In this work we show how to write $\alpha$ as a sum of symbols from $H^n(F,\mu_{p^{…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3302:field_when:0:110
SUMMARY:הקשר המיסטי האסטרונומי בין שנת המבול לבין שנת חורבן בית המקדש הראשון.
DTSTART:2021-12-21T15:45:00
DTEND:2021-12-21T16:30:00
DSCRIPTION:Speaker: פרופ' אמ' אריאל כהן, האוניברסיטה העברית \n
Abstract:
בפרק ט' של קידוש החודש במשנה תורה של הרמב"ם מודגש כי מקובל היה ע"י חז"ל שבשנת בריאת העולם חל המולד של חודש ניסן ביום רביעי בשבוע יום בו החלה תקופת ניסן: השמש, הירח ותחילת מזל טלה היו בקו אחד. אנו נראה, עפ"י מקור עתיק יומין, כי מצב זה התקיים גם בשנת יציאת מצריים ובשנת בניין בית המקדש. אנו מסיקים מכך שציון הדרך האסטרונומי של אירועים מרכזיים חיוביים בתולדות עם ישראל המתוארים בתנ"ך הוא מצב בו השמש והירח נמצאים בתוך מעלת האורך השמימית הראשונה של גלגל הזודיאק (תחילת האביב). לאור מסקנה זו…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3288:field_when:0:111
SUMMARY:Total variation cutoff for the transpose top-2 with random shuffle
DTSTART:2021-12-19T12:05:00
DTEND:2021-12-19T13:30:00
DSCRIPTION:Speaker: Subhajit Ghosh (BIU)\n
Abstract:
In this talk, we focus on the properties of a random walk on the alternating group $A_n$ generated by $3$-cycles of the form $(i,n-1,n)$ and $(i,n,n-1)$. We call this the transpose top-$2$ with random shuffle. We find the spectrum of the transition matrix of this shuffle. We show that the mixing time is of order $\left(n-\frac{3}{2}\right)\log n$ and prove that there is a total variation cutoff for this shuffle.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3289:field_when:0:112
SUMMARY:Genericity results for metric graphs and the trace space.
DTSTART:2021-12-18T22:00:00
DTEND:2021-12-19T11:30:00
DSCRIPTION:Speaker: Lior Alon, IAS\n
Abstract:
If you choose a random symmetric matrix, would it have two equal eigenvalues? Probably not, since symmetric matrices with degenerate eigenvalues capture a "very small portion" of the entire space of symmetric matrices. This is an example of a genericty result. A more complicated and famous result in spectral geometry is Uhlenbeck's genericity theorem ('72) which states that given any manifold, for a Baire-generic choice of Riemannian metric, all eigenvalues of the associated…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3284:field_when:0:113
SUMMARY:Quadratic Chabauty and beyond
DTSTART:2021-12-15T08:30:00
DTEND:2021-12-15T09:30:00
DSCRIPTION:Speaker: Dr. David Corwin (Ben-Gurion University of the Negev)\n
Abstract:
I will describe my work (some joint with I. Dan-Cohen) to extend the computational boundary of Kim's non-abelian Chabauty's method beyond the highly-studied Quadratic Chabauty. Faltings' Theorem says that the number of rational points on curves of higher genus is finite, and non-abelian Chabauty provides a blueprint both for proving this finiteness and for computing the sets of rational points. We first review classical Chabauty-Coleman, which does the same but works only for certain…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3286:field_when:0:114
SUMMARY:Forcing-theoretic approach to universal homogeneous structures, part 4
DTSTART:2021-12-14T12:00:00
DTEND:2021-12-14T14:00:00
DSCRIPTION:Speaker: Ziemek Kostana (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3282:field_when:0:115
SUMMARY:Graphs, stable permutations, and Cuntz algebra automorphisms
DTSTART:2021-12-12T12:00:00
DTEND:2021-12-12T13:30:00
DSCRIPTION:Speaker: Francesco Brenti (University of Rome II)\n
Abstract:
Stable permutations are a class of permutations that arises
in the study of the automorphism group of the Cuntz algebra.
In this talk I will define stable permutations, explain the
connection to the automorphisms of the Cuntz algebra, and
describe the main results known about them. I will then
present a characterization of stable permutations in terms
of certain associated graphs. As a consequence of this
characterization I will prove a conjecture in [Advances in Math.,
381(2021)…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3283:field_when:0:116
SUMMARY:Non-Parametric Estimation of Manifolds from Noisy Data
DTSTART:2021-12-11T22:00:00
DTEND:2021-12-12T11:30:00
DSCRIPTION:Speaker: Yariv Aizenbud, Yale\n
Abstract:
In many data-driven applications, the data follows some geometric structure, and the goal is to recover this structure. In many cases, the observed data is noisy and the recovery task is even more challenging. A common assumption is that the data lies on a low dimensional manifold. Estimating a manifold from noisy samples has proven to be a challenging task. Indeed, even after decades of research, there was no (computationally tractable) algorithm that accurately estimates a manifold…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3254:field_when:0:117
SUMMARY:The Hausdorff dimensions of branch groups
DTSTART:2021-12-08T08:30:00
DTEND:2021-12-08T09:30:00
DSCRIPTION:Speaker: Dr. Anitha Thillaisundaram (Lund University)\n
Abstract:
The concept of Hausdorff dimension was defined in the 1930s and
was originally applied to fractals and shapes in nature. However, from the
work of Abercrombie, Barnea and Shalev in the 1990s, the computation of
the Hausdorff dimensions in profinite groups has been made possible.
Starting with Abert and Virag's well-known result that there are groups
acting on a rooted tree with all possible Hausdorff dimensions,
mathematicians have been interested in computing the Hausdorff dimensions…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3281:field_when:0:118
SUMMARY:Forcing-theoretic approach to universal homogeneous structures, part 3
DTSTART:2021-12-07T12:00:00
DTEND:2021-12-07T14:00:00
DSCRIPTION:Speaker: Ziemek Kostana (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3280:field_when:0:119
SUMMARY:The second bounded cohomology of groups of homeomorphisms of 1-manifolds and some applications
DTSTART:2021-12-01T08:30:00
DTEND:2021-12-01T09:30:00
DSCRIPTION:Speaker: Prof. Yash Lodha( (University of Vienna)\n
Abstract:
In this talk I will describe some new computations of the second bounded cohomology (with trivial real coefficients) of a large class of groups of homeomorphisms of 1-manifolds. I will also discuss applications of this to some problems concerning the spectrum of stable commutator length of finitely presented groups and simplicial volume of manifolds. This is joint work with Francesco Fournier-Facio.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3278:field_when:0:120
SUMMARY:Forcing-theoretic approach to universal homogeneous structures, part 2
DTSTART:2021-11-30T12:00:00
DTEND:2021-11-30T14:00:00
DSCRIPTION:Speaker: Ziemek Kostana (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3276:field_when:0:121
SUMMARY:Cyclic descent extensions on roots of unity in the symmetric group
DTSTART:2021-11-28T12:00:00
DTEND:2021-11-28T13:30:00
DSCRIPTION:Speaker: Yuval Hovannes Khachatryan-Raziel\n
Abstract:
The cyclic descent statistic that can be defined on certain permutation sets and other combinatorial objects, as a cyclic equivariant extension of the classical descent statistic. Cyclic descents were introduced by Klyachko and Cellini in the late 20th century, and further studied by many. An axiomatic approach was presented by Rhoades, further developed by Adin, Reiner and Roichman and others.
In a recent work, Adin, Hegedus and Roichman characterize the conjugacy classes in the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3277:field_when:0:122
SUMMARY:Big Fiber Theorems and Ideal-Valued Measures in Symplectic Topology
DTSTART:2021-11-27T22:00:00
DTEND:2021-11-28T11:30:00
DSCRIPTION:Speaker: Yaniv Ganor, Technion\n
Abstract:
In various areas of mathematics there exist "big fiber theorems", these are theorems of the following type: "For any map in a certain class, there exists a 'big' fiber", where the class of maps and the notion of size changes from case to case. We will discuss three examples of such theorems, coming from combinatorics, topology and symplectic topology from a unified viewpoint provided by Gromov's notion of ideal-valued measures. We adapt the latter notion to the realm of symplectic…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3274:field_when:0:123
SUMMARY:Forcing-theoretic approach to universal homogeneous structures, part 1
DTSTART:2021-11-23T12:00:00
DTEND:2021-11-23T14:00:00
DSCRIPTION:Speaker: Ziemek Kostana (BIU)\n
Abstract:
In this series of talks, we will investigate relations between generic first-order structures added by forcing, and universal homogeneous structures arising from the Fraisse theory. During the first talk, I intend to give a self-contained introduction to the Fraisse theory, define forcings Fn(\kappa, K, \lambda), and explain why are they provide a reasonable generalization of Fraisse theory to higher cardinalities.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3273:field_when:0:124
SUMMARY:Some natural extensions of the parking space
DTSTART:2021-11-21T12:00:00
DTEND:2021-11-21T13:30:00
DSCRIPTION:Speaker: Matjaž Konvalinka (University of Ljubljana)\n
Abstract:
We will construct a family of S_n modules with the property
that upon restriction to S_{n-1} they recover the classical parking
function representation of Haiman. The representation is conjecturally
isomorphic to a construction from Berget--Rhoades. We will also
mention some (conjectured) connections with Donaldson--Thomas
invariants of the m-loop quiver.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3275:field_when:0:125
SUMMARY:Near-integrable systems in high dimensions: slow equilibration and chaos
DTSTART:2021-11-20T22:00:00
DTEND:2021-11-21T11:30:00
DSCRIPTION:Speaker: Tomer Goldfriend, Weizmann Institute of Science\n
Abstract:
Hamiltonian integrable models are essentially the simplest volume preserving dynamical systems: their flow is quasi-periodic along invariant tori, defined by a large set of conserved functions. These systems are non-ergodic and non-chaotic. The interest in near-integrable systems--- where the set of conservation laws is slightly perturbed--- goes back to Laplace and Lagrange studies on the stability of the Solar System. While integrability breaking in low dimensions can be fully…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3272:field_when:0:126
SUMMARY:Pairwise far Souslin trees
DTSTART:2021-11-16T12:00:00
DTEND:2021-11-16T14:00:00
DSCRIPTION:Speaker: Shira Greenstein (BIU)\n
Abstract:
We will present a construction of a family of 2^kappa many kappa-Souslin trees for which the product of any finitely many of them is still kappa-Souslin. The proof uses the Brodsky-Rinot proxy principle and hence applies to any regular uncountable cardinal kappa.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3270:field_when:0:127
SUMMARY:Order and disorder in multiscale substitution tilings
DTSTART:2021-11-14T14:00:00
DTEND:2021-11-14T15:30:00
DSCRIPTION:Speaker: Yotam Smilansky, Rutgers\n
Abstract:
The study of aperiodic order and mathematical models of quasicrystals is concerned with ways in which disordered structures can nevertheless manifest aspects of order. In the talk I will describe examples such as the aperiodic Penrose and pinwheel tilings, together with several geometric, functional, dynamical and spectral properties that enable us to measure how far such constructions are from demonstrating lattice-like behavior. A particular focus will be given to new results on …
END:VEVENT
BEGIN:VEVENT
UID:calendar:3271:field_when:0:128
SUMMARY:On a poset of set partitions
DTSTART:2021-11-14T12:00:00
DTEND:2021-11-14T13:30:00
DSCRIPTION:Speaker: Yonah Cherniavsky (Ariel Univ.)\n
Abstract:
We define combinatorially a partial order on the set partitions.
This order appears to be equivalent to the Bruhat–Chevalley–Renner order on the upper triangular matrices.
We exhibit a connection between two statistics on set partitions --
the intertwining number (introduced by Richard Ehrenborg and Margaret Readdy in 1998)
and the depth-index (our parameter which is the rank function of our poset of set partitions).
This talk is based on joint works with Mahir Bilen Can and…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3253:field_when:0:129
SUMMARY:Graded submodule zeta functions of pattern algebras
DTSTART:2021-11-10T08:30:00
DTEND:2021-11-10T09:30:00
DSCRIPTION:Speaker: Marlies Vantomme (Bielefeld University)\n
Abstract:
(Graded) Submodule zeta functions are complex functions that are associated to an algebra of endomorphisms of a module. Pattern algebras are examples of such algebras of endomorphisms. In this talk, I will introduce these terms and discuss some properties of the (graded) submodule zeta functions associated to pattern algebras. I will also explain how the results for pattern algebras relate to general conjectures about submodule zeta functions…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3267:field_when:0:130
SUMMARY:Cofinal types on w1 and w2, part 8
DTSTART:2021-11-09T12:00:00
DTEND:2021-11-09T14:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3250:field_when:0:131
SUMMARY:Enumeration of chains in partially ordered sets and polynomials with only real roots
DTSTART:2021-11-07T12:00:00
DTEND:2021-11-07T13:30:00
DSCRIPTION:Speaker: Christos Athanasiadis (Univ. of Athens)\n
Abstract:
The coefficients of the chain polynomial of a finite poset
enumerate chains in the poset by their number of elements. The chain
polynomials of geometric lattices are conjectured in this talk to have
only real roots and the analogous question is discussed for other
important classes of Cohen--Macaulay posets. Among other partial
results, the conjecture is proven for the subspace and the partition
lattices. An application to the face enumeration of the second
barycentric subdivision of…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3248:field_when:0:132
SUMMARY:Cofinal types on w1 and w2, part 7
DTSTART:2021-11-02T12:00:00
DTEND:2021-11-02T14:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3249:field_when:0:133
SUMMARY:Ribbon Matrices
DTSTART:2021-10-31T12:00:00
DTEND:2021-10-31T13:30:00
DSCRIPTION:Speaker: Harel Rozenfeld (BIU)\n
Abstract:
An r-ribbon tableau of shape λ⊢ rn is a filling of the cells of the diagram [λ] by the letters 1, . . . , n
such that each letter fills exactly r cells, which form a ribbon shape,
and for each 1 ≤ k ≤ n, the union of the i-th ribbons for 1 ≤ i ≤ k is a diagram of ordinary shape.
A ribbon matrix of order n is an n-ribbon tableau whose shape is an nxn square.
We present a new bijection from the set of ribbon matrices of order nxn to the set of permutations in the symmetric…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3246:field_when:0:134
SUMMARY:Interval exchange transformations, Rauzy graphs, Universal sequences and factor-Dynamics.
DTSTART:2021-10-30T21:00:00
DTEND:2021-10-30T23:30:00
DSCRIPTION:Speaker: Alexei Kanel-Belov , Bar-Ilan University\n
Abstract:
Let $M$ be a compact metric space, $U\subset M$ be its open subspace, $f:M\to M$ be a homeomorphism of the compact into itself, and $x\in M$ be an initial point. It determines sequence of points
$x,f(x),\ldots,f^{(n)}(x),\ldots$ With the sequence of iterations, one can associate an infinite binary word $w_n=a$ for $f^{(n)}(x_0)\in U$, $w_n=b$ for $f^{(n)}(x_0)\notin U$
which is called the {\it evolution} of point $x_0$. If $f$ is invertible then $n\in \mathbb{Z}$, otherwise $n\in \…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3245:field_when:0:135
SUMMARY:Cofinal types on w1 and w2, part 6
DTSTART:2021-10-26T11:00:00
DTEND:2021-10-26T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3243:field_when:0:136
SUMMARY:Counting and combinatorics in aperiodic order
DTSTART:2021-10-24T11:00:00
DTEND:2021-10-24T12:30:00
DSCRIPTION:Speaker: Yotam Smilansky, Rutgers\n
Abstract:
Combinatorial objects and methods naturally appear in the study of aperiodic order and mathematical quasicrystals. In the talk I will describe how aspects of matchings, graphs, counting and discrepancy can imply results on certain measures of order and disorder in long-range geometry, with applications to classical constructions such as the Penrose tiling as well as to recent developments in aperiodic order. Partially based on joint work with Yaar Solomon.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3244:field_when:0:137
SUMMARY:Tiling the integers with translates of one tile: the Coven-Meyerowitz tiling conditions for three prime factors
DTSTART:2021-10-24T09:00:00
DTEND:2021-10-24T10:30:00
DSCRIPTION:Speaker: Itay Londner, Weizmann Institute of Science\n
Abstract:
It is well known that if a finite set of integers A tiles the integers by translations, then the translation set must be periodic, so that the tiling is equivalent to a factorization A+B=Z_M of a finite cyclic group. Coven and Meyerowitz (1998) proved that when the tiling period M has at most two distinct prime factors, each of the sets A and B can be replaced by a highly ordered "standard" tiling complement. It is not known whether this behaviour persists for all tilings with no…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3240:field_when:0:138
SUMMARY:Higher dimensional analogue of cyclicity over $p$-adic curves
DTSTART:2021-10-20T07:30:00
DTEND:2021-10-20T08:30:00
DSCRIPTION:Speaker: Dr. Saurabh Gosavi (Bar-Ilan University)\n
Abstract:
Recall that every division algebra over a number field is cyclic. In this talk, we will show a higher dimensional analogue of this classical fact. More precisely, let $F$ be the function field of a curve over a non-archimedean local field. Let $m \geq 2$ be an integer coprime to the characteristic of the residue field. We will show that every element in $H^{3}(F, \mu_{m}^{\otimes 2})$ is a symbol. This extends a result of Parimala and Suresh where they show this when $m$ is prime and…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3242:field_when:0:139
SUMMARY:On Multicolor Ramsey Numbers and Subset-Coloring of Hypergraphs
DTSTART:2021-10-17T13:00:00
DTEND:2021-10-17T13:00:00
DSCRIPTION:Speaker: Chaya Keller (Ariel Univ.)\n
Abstract:
The multicolor hypergraph Ramsey number Rk(s,r) is the minimal n, such that in any k-coloring of all r-element subsets of [n], there is a subset of size s, all whose r-subsets are monochromatic.
We present a new "stepping-up lemma" for Rk(s,r): If Rk(s,r)>n, then Rk+3(s+1,r+1)>2n. Using the lemma, we improve some known lower bounds on multicolor hypergraph Ramsey numbers.
Furthermore, given a hypergraph H=(V,E), we consider the Ramsey-like problem of coloring all r-…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3241:field_when:0:140
SUMMARY:A topological view of the Lorenz equations
DTSTART:2021-10-17T09:00:00
DTEND:2021-10-17T10:30:00
DSCRIPTION:Speaker: Tali Pinsky, Technion\n
Abstract:
The Lorenz equations are a classical example of a chaotic flow in R^3. As they are hard to analyze, a simpler geometric model that is chaotic in the same way has been proposed. Smale’s 14th problem was to prove that the original Lorenz flow is equivalent to the geometric model.In this talk I intend to describe the geometric model and a recent extension that preserves more of the global topology of the flow. I’ll explain how this new model is strongly related to the geodesic flow on…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3236:field_when:0:141
SUMMARY:Cofinal types on w1 and w2, part 5
DTSTART:2021-10-12T11:00:00
DTEND:2021-10-12T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3235:field_when:0:142
SUMMARY:Cofinal types on w1 and w2, part 4
DTSTART:2021-10-07T11:00:00
DTEND:2021-10-07T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3234:field_when:0:143
SUMMARY:Cofinal types on w1 and w2, part 3
DTSTART:2021-09-30T11:00:00
DTEND:2021-09-30T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3233:field_when:0:144
SUMMARY:Cofinal types on w1 and w2, part 2
DTSTART:2021-09-14T11:00:00
DTEND:2021-09-14T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3232:field_when:0:145
SUMMARY:Cofinal types on w1 and w2, part 1
DTSTART:2021-08-31T11:00:00
DTEND:2021-08-31T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
This is a series of talks motivated by a recent paper by Kuzeljevic and Todorcevic
END:VEVENT
BEGIN:VEVENT
UID:calendar:3231:field_when:0:146
SUMMARY:Higher-dimensional Delta-systems
DTSTART:2021-08-17T11:00:00
DTEND:2021-08-17T13:00:00
DSCRIPTION:Speaker: Ari Brodsky (SCE)\n
Abstract:
We present a result of Chris Lambie-Hanson, investigating higher-dimensional Δ-systems, isolating a particular definition thereof and proving a higher-dimensional version of the classical Δ-system lemma.
https://arxiv.org/abs/2006.01086
END:VEVENT
BEGIN:VEVENT
UID:calendar:3230:field_when:0:147
SUMMARY:The dominating number at singular strong limits, part 3
DTSTART:2021-08-10T11:00:00
DTEND:2021-08-10T13:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3227:field_when:0:148
SUMMARY:Incompactness of the second uncountable cardinal
DTSTART:2021-08-03T11:00:00
DTEND:2021-08-03T13:00:00
DSCRIPTION:Speaker: Assaf Rinot (BIU)\n
Abstract:
In a celebrated paper from 1997, Shelah proved that Pr1(w2,w2,w2,w) is a theorem of ZFC, and it remains open ever since whether moreover Pr1(w2,w2,w2,w1) holds.
In an unpublished note from 2017, Todorcevic proved that a certain weakening of the latter follows from CH.
In a recent paper with Zhang (arXiv:2104.15031), we gave a few weak sufficient conditions for Pr1(w2,w2,w2,w1) to hold.
In an even more recent paper (arXiv:1910.02419v2), Shelah proved that it holds, assuming the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3225:field_when:0:149
SUMMARY:The dominating number at singular strong limits, part 2
DTSTART:2021-07-27T11:00:00
DTEND:2021-07-27T13:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3222:field_when:0:150
SUMMARY:The dominating number at singular strong limits, part 1
DTSTART:2021-07-20T11:00:00
DTEND:2021-07-20T13:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
I will talk about the principle SEP of Shelah. As an application, I will prove a result from Shelah 1159, that the dominating number always takes the maximal value at a strong limit singular cardinal.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3221:field_when:0:151
SUMMARY:Coloring cubes, part 3
DTSTART:2021-07-13T11:00:00
DTEND:2021-07-13T13:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
last talk for this series
END:VEVENT
BEGIN:VEVENT
UID:calendar:3303:field_when:0:152
SUMMARY:פשר עזרא- 'ספר העבור' לרבי אברהם אבן עזרא מבוא למהדורה מוערת
DTSTART:2021-07-12T14:45:00
DTEND:2021-07-12T15:30:00
DSCRIPTION:Speaker: ד"ר ערן רביב, בר -אילן \n
Abstract:
ר' אברהם אבן עזרא היה מלומד בתחומים רבים ובין היתר בנושאי לוח השנה. הוא נולד בספרד בסוף המאה ה- 11, בשנות הארבעים לחייו נדד לצפון אפריקה ומאוחר יותר לאיטליה צרפת ואנגליה.
בשנות החמישים לחייו במהלך שהותו באירופה חיבר את ספר העיבור על כללי לוח השנה.
בשנת 1874 הוציא לאור שלמה זלמן חיים הלברשטאם את הספר בהוצאת מקיצי נרדמים.
הוצאה זו היא הוצאה חלקית שכן חלק מהחומר שכתב האב"ע במקור לא היה בנמצא בכתבי היד של המהדיר. בנוסף היות והמו"ל לא ירד לסוף דעתו של האב"ע נפלו שיבושים בהוצאה. …
END:VEVENT
BEGIN:VEVENT
UID:calendar:3218:field_when:0:153
SUMMARY:Coloring cubes, part 2
DTSTART:2021-06-22T11:00:00
DTEND:2021-06-22T13:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3212:field_when:0:154
SUMMARY:מבוא לקמירות; תורת ברון-מינקובסקי
DTSTART:2021-06-17T15:00:00
DTEND:2021-06-17T16:00:00
DSCRIPTION:Speaker: דן פלורנטין\n
Abstract:
תכונת הקמירות הופיעה כבר בימי קדם (בכתביהם של אריסטו, ארכימדס), אבל נחקרה לעומק רק בתקופה המודרנית (100-150 השנים האחרונות).
בהרצאה זו נתאר נקודות מפתח בהתפתחות הידע על גופים קמורים (למשל משפט מינקובסקי, אי שווין ברון-מינקובסקי), ונדון בקשר לגיאומטריה ואנליזה (לדוגמא, האי שוויון האיזופרימטרי). כמו כן תראו כמה התנהגויות מפתיעות של גופים קמורים במימד גבוה.
הרקע הנדרש להרצאה מוכל בקורסי הבסיס של התואר הראשון.
סטודנטים שמחפשים הנחיה או מתעניינים בתחום מוזמנים במיוחד!
END:VEVENT
BEGIN:VEVENT
UID:calendar:3211:field_when:0:155
SUMMARY:Minimal weights of mod p Galois representations
DTSTART:2021-06-16T07:30:00
DTEND:2021-06-16T08:30:00
DSCRIPTION:Speaker: Hanneke Wiersema (King's College London)\n
Abstract:
The strong form of Serre's conjecture states that every two-dimensional continuous, odd, irreducible mod p representation of the absolute Galois group of Q arises from a modular form of a specific minimal weight, level and character. In this talk we show the minimal weight is equal to a notion of minimal weight inspired by work of Buzzard, Diamond and Jarvis. Moreover, using the Breuil-Mézard conjecture we give a third interpretation of this minimal weight as the smallest k>1 such…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3219:field_when:0:156
SUMMARY:Coloring cubes, part 1
DTSTART:2021-06-08T11:00:00
DTEND:2021-06-08T13:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We discuss colorings of triples
END:VEVENT
BEGIN:VEVENT
UID:calendar:3206:field_when:0:157
SUMMARY:Flag Hilbert-Poincaré series and Igusa zeta functions of hyperplane arrangements
DTSTART:2021-06-02T07:30:00
DTEND:2021-06-02T08:30:00
DSCRIPTION:Speaker: Dr. Joshua Maglione (Bielefeld University)\n
Abstract:
We define a class of multivariate rational functions associated with
hyperplane arrangements called flag Hilbert-Poincaré series, and we show that
these rational functions are closely related to enumeration problems
from algebra. We report on a general self-reciprocity result and explore
other connections within algebraic combinatorics via Hilbert series of
Stanley-Reisner rings. This is joint work with Christopher Voll.
=============================================…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3209:field_when:0:158
SUMMARY:Kurepa trees and ccc forcing
DTSTART:2021-06-01T11:00:00
DTEND:2021-06-01T13:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
Results on the Generic Kurepa Hypothesis
END:VEVENT
BEGIN:VEVENT
UID:calendar:3204:field_when:0:159
SUMMARY:Kurepa trees, part 4
DTSTART:2021-05-25T11:00:00
DTEND:2021-05-25T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3205:field_when:0:160
SUMMARY:On the matrix of local coefficients and the restriction problem
DTSTART:2021-05-23T09:00:00
DTEND:2021-05-23T10:00:00
DSCRIPTION:Speaker: Dani Szpruch (Open University)\n
Abstract:
Langlands-Shahidi method is one of the main ways to study automorphic L-functions for quasi-split algebraic groups. This method is centered around Shahidi local coefficients arising from a certain uniqueness result. In this talk we shall recall the definition of these coefficients and discuss a local application. Then we shall describe an analog of these coefficients for covering groups defined in a setting where the uniqueness mentioned above fails. Finally, we shall discuss the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3200:field_when:0:161
SUMMARY:A model theory of modular curves
DTSTART:2021-05-09T09:00:00
DTEND:2021-05-09T10:00:00
DSCRIPTION:Speaker: Boris Zilber (University of Oxford)\n
Abstract:
I am going to discuss a progress in a project which aims to formalise the notion of an analytic covering space of a complex algebraic variety
in such a way that the formal pseudo-analytic cover is unique up to abstract isomorphisms. At this stage our interest focuses on the upper half-plane as the cover of modular curves.
On the model theory side it is based on Shelah's theory of abstract elementary classes. On the geometric side it uses the rich theory of complex multiplication…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3201:field_when:0:162
SUMMARY:Kurepa trees, part 3
DTSTART:2021-05-04T11:00:00
DTEND:2021-05-04T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3199:field_when:0:163
SUMMARY:https://us02web.zoom.us/j/89074854473?pwd=R1BWVEZ4NG5yMkhNYVB2RGRLVnNMdz09
DTSTART:2021-05-02T09:00:00
DTEND:2021-05-02T10:00:00
DSCRIPTION:Speaker: Danylo Radchenko (ETH, Zurich)\n
Abstract:
In this talk I will explain the Cohn-Kumar conjecture
about energy minimization in Euclidean spaces, its connection to
the sphere packing problem and its recent solution in 8 and 24 dimensions
based on some novel interpolation formulas for radial Fourier eigenfunctions.
The talk is based on a joint work with H. Cohn, A. Kumar, S.D. Miller, and M. Viazovska.
ZOOM:
https://us02web.zoom.us/j/89074854473?pwd=R1BWVEZ4NG5yMkhNYVB2RGRLVnNMd…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3202:field_when:0:164
SUMMARY:Kurepa trees, part 2
DTSTART:2021-04-27T11:00:00
DTEND:2021-04-27T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3198:field_when:0:165
SUMMARY:Strong Prikry Property for Magidor Iteraton, part 3
DTSTART:2021-04-21T11:00:00
DTEND:2021-04-21T13:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
link to recording
END:VEVENT
BEGIN:VEVENT
UID:calendar:3203:field_when:0:166
SUMMARY:Kurepa trees, part 1
DTSTART:2021-04-20T11:00:00
DTEND:2021-04-20T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We discuss consistency results concerning Kurepa trees
END:VEVENT
BEGIN:VEVENT
UID:calendar:3196:field_when:0:167
SUMMARY:Homomorphic encryption and some black box attacks
DTSTART:2021-04-11T09:00:00
DTEND:2021-04-11T10:00:00
DSCRIPTION:Speaker: Alexandre Borovik, University of Manchester\n
Abstract:
We offer a systematic approach to a class of attacks on communication
channels protected by homomorphic encryption based on black box
algebraic analysis. Our conclusion is that wide classes of algebraic
structures should not be used as ambient structures for homomorphic
encryption. We give some examples for groups and rings, but our general
methodology is much wider applicable.
Black box algebra deals with a category where objects are finite
algebraic structures (fields, rings, group…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3195:field_when:0:168
SUMMARY:Strong Prikry Property for Magidor Iteraton, part 2
DTSTART:2021-04-07T11:00:00
DTEND:2021-04-07T13:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
In his celebrated work on the identity crisis of strongly compact cardinals, Magidor introduced a special iteration of Prikry forcings for a set of measurable cardinals, known as the Magidor iteration.
The purpose of this talk is to state and prove a version of the strong Prikry Lemma for such iterations, extending a result of Fuchs for the case where the set of measurables is discrete. We will also describe several applications regarding the genericity of sequences of critical…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3194:field_when:0:169
SUMMARY:The tropicalization of non-archimedean convex semialgebraic sets and its relation with mean payoff games
DTSTART:2021-04-07T07:30:00
DTEND:2021-04-07T08:30:00
DSCRIPTION:Speaker: Prof. Stephane Gaubert (INRIA and CMAP, Ecole Polytechnique, IP Paris, CNRS)\n
Abstract:
Convex sets can be defined over ordered fields with a non-archimedean valuation. Then, tropical convex sets arise as images by the valuation of non-archimedean convex sets. The tropicalizations of polyhedra and spectrahedra are of special interest, since they can be described in terms of deterministic and stochastic games with mean payoff. In that way, one gets a correspondence between classes of zero-sum games, with an unsettled complexity, and classes of semialgebraic convex…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3193:field_when:0:170
SUMMARY:The strong Prikry Property for Magidor iterations
DTSTART:2021-03-24T12:00:00
DTEND:2021-03-24T14:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
In his celebrated work on the identity crisis of strongly compact cardinals, Magidor introduced a special iteration of Prikry forcings for a set of measurable cardinals, known as the Magidor iteration.
The purpose of this talk is to state and prove a version of the strong Prikry Lemma for such iterations, extending a result of Fuchs for the case where the set of measurables is discrete. We will also describe several applications regarding the genericity of sequences of critical…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3192:field_when:0:171
SUMMARY:Non-existence of bi-infinite polymer Gibbs measures on Z^2
DTSTART:2021-03-21T10:00:00
DTEND:2021-03-21T11:00:00
DSCRIPTION:Speaker: Ofer Busani, University of Bristol\n
Abstract:
To each vertex x\in Z^2 assign a positive weight \omega_x. A geodesic between two ordered points on the lattice is an up-right path maximizing the cumulative weight along itself. A bi-infinite geodesic is an infinite path taking up-right steps on the lattice and such that for every two points on the path, its restriction to between the points is a geodesic. Assume the weights across the lattice are i.i.d., does there exist a bi-infinite geodesic with some positive probability?
In…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3191:field_when:0:172
SUMMARY:Computers as novel mathematical reality
DTSTART:2021-03-14T10:00:00
DTEND:2021-03-14T11:00:00
DSCRIPTION:Speaker: Nikolai Vavilov, St. Petersburg State University\n
Abstract:
In the last decades there was much ado about computer proofs, computer aided proofs,
computer verified proofs, and the like. It is obvious that the advent and proliferation of
computers have drastically changed applications of mathematics.
What one discusses much less, however, and what I find much more interesting, is how
computers have changed mathematics itself, and mathematicians’ stance in regard of
mathematical reality, both as far as the possibilities to immediately…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3190:field_when:0:173
SUMMARY:Stationary reflection and Prikry forcing, part 2
DTSTART:2021-03-10T12:00:00
DTEND:2021-03-10T14:00:00
DSCRIPTION:Speaker: Yair Hayut (HUJI)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3185:field_when:0:174
SUMMARY:Generating algebras over commutative rings
DTSTART:2021-03-10T08:30:00
DTEND:2021-03-10T09:30:00
DSCRIPTION:Speaker: Dr. Uriya First (Haifa University)\n
Abstract:
Let R be a noetherian (commutative) ring of Krull dimension d. A classical theorem of Forster states that a rank-n locally free R-module can be generated by n+d elements. Swan and Chase observed that this upper bound cannot be improved in general. I will discuss a joint work with Zinovy Reichstein and Ben Williams where similar upper and lower bounds are obtained for R-algebras, provided that R is of finite type over an infinite field k. For example, every Azumaya R-algebra of degree…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3188:field_when:0:175
SUMMARY:The shift action on independent random variables
DTSTART:2021-03-07T10:00:00
DTEND:2021-03-07T11:00:00
DSCRIPTION:Speaker: Zemer Kosloff, Hebrew University of Jerusalem\n
Abstract:
The Bernoulli shift model which is the action on a sequence of i.i.d. random variables by time shifts in one of the central examples of classical ergodic theory. To this date much is known on the ergodic theoretic properties of this model. A notable example is Sinai factor theorem which says that if a given system has positive entropy (is chaotic) then it has Bernoulli shift models as factors (subsystems) which leads to one of the most common definitions of chaos. In addition,…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3186:field_when:0:176
SUMMARY:Stationary reflection and Prikry forcing, part 1
DTSTART:2021-03-03T12:00:00
DTEND:2021-03-03T14:00:00
DSCRIPTION:Speaker: Yair Hayut (HUJI)\n
Abstract:
In 1982, Magidor proved the consistency of stationary reflection at \aleph_{\omega+1}, relative to an \omega-sequence of supercompact cardinals.
Square based heuristics indicated that a much weaker large cardinal hypothesis is the correct strength.
In a sequence of results of various authors, Magidor's result was gradually improved to stationary reflection at all sets except one "bad" stationary set at \aleph_{\omega+1}, starting with a large cardinal property weaker than \…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3180:field_when:0:177
SUMMARY:All colorings are strong, but some colorings are stronger than the others
DTSTART:2021-02-24T12:00:00
DTEND:2021-02-24T14:00:00
DSCRIPTION:Speaker: Assaf Rinot (BIU)\n
Abstract:
Strong colorings are everywhere - they can be obtained from analysis of basis problems, transfinite diagonalizations, oscillations, or walks on ordinals. They give rise to interesting topological spaces and partial orders.
In this talk, I'll be looking at all aspects mentioned above, reporting on findings from my joint projects with Kojman, Lambie-Hanson, Inamdar, Steprans and Zhang.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3184:field_when:0:178
SUMMARY:Hasse-Schmidt derivations on Grassmann semi-algebras
DTSTART:2021-02-24T08:30:00
DTEND:2021-02-24T09:30:00
DSCRIPTION:Speaker: Prof. Letterio Gatto (Politecnico di Torino)\n
Abstract:
The talk will be split into two parts. The first will be about the notion of Hasse-Schmidt derivation on a classical exterior algebra, which I introduced years ago to deal with Schubert calculus for complex Grassmannians. In this first part, I will focus on the purely combinatorial features of the construction suited to be transferred in the second part of the talk, concerned with some joint work in progress with Louis Rowen and Adam Chapman. The new framework will be the more general…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3182:field_when:0:179
SUMMARY:The spectra of cardinalities of branches of Kurepa trees, part 2
DTSTART:2021-02-17T12:00:00
DTEND:2021-02-17T14:00:00
DSCRIPTION:Speaker: Mark Poor (HUJI)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3181:field_when:0:180
SUMMARY:The spectra of cardinalities of branches of Kurepa trees, part 1
DTSTART:2021-02-10T12:00:00
DTEND:2021-02-10T14:00:00
DSCRIPTION:Speaker: Mark Poor (HUJI)\n
Abstract:
We study the possible values of the Kurepa spectra, i.e. how the set of cardinalities of branches of Kurepa trees may look like. It turns out that assuming GCH below the second uncountable cardinal (and possibly the existence of an inaccessible) we can force every set of cardinals (satisfying some obvious necessary conditions) to be the Kurepa spectrum.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3177:field_when:0:181
SUMMARY:Fresh subsets of measurable ultrapowers
DTSTART:2021-01-27T12:00:00
DTEND:2021-01-27T14:00:00
DSCRIPTION:Speaker: Philip Luecke (Barcelona)\n
Abstract:
In my talk, I want to present recent results studying the closure
and non-closure properties of measurable ultrapowers with respect to Hamkin's
notion of freshness. These results show that the extent of these properties
highly depends on the combinatorics of the underlying model of set theory.
While a result of Sakai shows that it is possible to obtain ultrapowers with
maximal closure properties by forcing over a model containing a strongly com-
pact cardinal, it turns out that…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3176:field_when:0:182
SUMMARY:Lafforgue pseudocharacters and the construction of Galois representations
DTSTART:2021-01-20T08:30:00
DTEND:2021-01-20T09:30:00
DSCRIPTION:Speaker: Dr. Ariel Weiss (Hebrew University of Jerusalem)\n
Abstract:
A key goal of the Langlands program is to attach Galois representations to automorphic representations. In general, there are two methods to construct these representations. The first, and the most effective, is to extract the Galois representation from the étale cohomology of a suitable Shimura variety. However, most Galois representations cannot be constructed in this way. The second, more general, method is to construct the Galois representation, via its corresponding…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3175:field_when:0:183
SUMMARY:Graphs of bounded shrub-depth, through a logic lens
DTSTART:2021-01-17T12:00:00
DTEND:2021-01-17T13:30:00
DSCRIPTION:Speaker: Yijia Chen (Fudan University)\n
Abstract:
Shrub-depth is a graph invariant often considered as an extension of tree-depth to dense graphs. In this talk I will explain our recent proofs of two results about graphs of bounded shrub-depth.
1. Every graph property definable in monadic-second order logic, e.g., 3-colorability, can be evaluated by Boolean circuits of constant depth and polynomial size, whose depth only depends on the shrub-depth of input graphs.
2. Graphs of bounded shrub-depth can be characterized by a finite set…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3173:field_when:0:184
SUMMARY:Universal functions, strong colourings and ideas from PID
DTSTART:2021-01-13T12:00:00
DTEND:2021-01-13T14:00:00
DSCRIPTION:Speaker: Juris Stperans (York)\n
Abstract:
A construction of Shelah will be reformulated using the PID to provide alternative models of the failure of CH and the existence of a universal colouring of cardinality . The impact of the range of the colourings will be examined. An application to the theory of strong colourings over partitions will also be given.
Links to the recording.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3172:field_when:0:185
SUMMARY:On the distribution of randomly signed sums and Tomaszewski’s conjecture
DTSTART:2021-01-10T12:00:00
DTEND:2021-01-10T13:30:00
DSCRIPTION:Speaker: Ohad Klein (Bar-Ilan University)\n
Abstract:
A Rademacher sum X is a random variable characterized by real numbers a_1, ..., a_n, and is equal to
X = a_1 x_1 + ... + a_n x_n,
where x_1, ..., x_n are independent signs (uniformly selected from {-1, 1}).
We discuss various aspects in which Rademacher sums behave "somewhat" like normally distributed variables.
A relevant puzzle by Bogusław Tomaszewski, 1986:
Is it true that all Rademacher sums X satisfy Pr[ |X| <= sqrt Var(X) ] >= 1/2 ?
(for normally distributed variables…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3169:field_when:0:186
SUMMARY:Equations of Modular Curves
DTSTART:2021-01-06T14:00:00
DTEND:2021-01-06T15:00:00
DSCRIPTION:Speaker: Eran Assaf, Dartmouth College\n
Abstract:
Modular curves are fundamental objects in modern number theory, which allow us to relate geometric objects and arithmetic ones. Recent advances towards long standing conjectures depend crucially on explicit computation of these objects. The talk will describe novel algorithms that achieve this goal.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3170:field_when:0:187
SUMMARY:Covering convex regions with unit discs
DTSTART:2021-01-03T12:00:00
DTEND:2021-01-03T13:30:00
DSCRIPTION:Speaker: Simi Haber (Bar-Ilan University)\n
Abstract:
Given a convex region C in the plane, how many unit discs are needed to cover it? This classic discrete geometry problem has real life applications in, e.g., placing cellular antennas.
A precise answer for the above question seems out of reach, even when C is a disc of a given radius. However, Blaschke, Toth and Hadwiger provided a nonconstructive upper bound for the number of required discs, as a function of the area and perimeter of C.
In this talk we will discuss an improved…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3174:field_when:0:188
SUMMARY:Actions of tame abelian product groups
DTSTART:2020-12-30T12:00:00
DTEND:2020-12-30T14:00:00
DSCRIPTION:Speaker: Assaf Shani (Harvard)\n
Abstract:
A Polish group G is tame if for any continuous action of G, the corresponding orbit equivalence relation is Borel. Suppose that G=\prod_n \Gamma_n is a product of countable abelian groups. It follows from results of Solecki and Ding-Gao that if G is tame, then all of its actions are in fact potentially \Pi^0_6. Ding and Gao conjectured that this bound could be improved to \Pi^0_3. We refute this, by finding an action of a tame abelian product group, which is not potentially \Pi^0_5.…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3168:field_when:0:189
SUMMARY:Minimal forms for conics
DTSTART:2020-12-30T08:30:00
DTEND:2020-12-30T09:30:00
DSCRIPTION:Speaker: Dr. Adam Chapman (Academic College of Tel Aviv-Yafo)\n
Abstract:
A conic is the Severi-Brauer variety of a quaternion algebra Q, and the question of which anisotropic quadratic forms become isotropic over the function field F_Q of a conic has puzzled algebraists for the last three decades. An anisotropic quadratic form is F_Q-minimal if it becomes isotropic over F_Q but any proper subform remains anisotropic. Minimal forms are known to have odd dimension, and examples of minimal forms of any odd dimension were constructed by Hoffmann and Van Geel…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3167:field_when:0:190
SUMMARY:Hyperpaths
DTSTART:2020-12-27T12:00:00
DTEND:2020-12-27T13:30:00
DSCRIPTION:Speaker: Amir Dahari (Hebrew University of Jerusalem)\n
Abstract:
Hypertrees are high-dimensional counterparts of graph theoretic trees. They have attracted a great deal of attention by various investigators.
Here we introduce and study {\em Hyperpaths} - a particular class of hypertrees which are high dimensional analogs of paths in graph theory. A $d$-dimensional hyperpath is a $d$-dimensional hypertree in which every $(d-1)$-dimensional face is contained…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3166:field_when:0:191
SUMMARY:S spaces and L spaces, part 2
DTSTART:2020-12-23T12:00:00
DTEND:2020-12-23T14:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
We introduce a new combinatorial principle which we call ♣_AD. This principle asserts the existence of a certain multi-ladder system with guessing and almost-disjointness features, and is shown to be sufficient for carrying out de Caux type constructions of topological spaces.
Our main result states that strong instances of ♣_AD follow from the existence of a Souslin tree. As an application, we obtain a simple, de Caux type proof of Rudin’s result that if there is a Souslin tree,…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3165:field_when:0:192
SUMMARY:Representability and boxicity of simplicial complexes
DTSTART:2020-12-20T12:00:00
DTEND:2020-12-20T13:30:33
DSCRIPTION:Speaker: Alan Lew (Technion)\n
Abstract:
An interval graph is the intersection graph of a family of intervals in the real line. Motivated by problems in ecology, Roberts defined the boxicity of a graph G to be the minimal k such that G can be written as the intersection of k interval graphs.
A natural higher dimensional generalization of interval graphs is the class of d-representable complexes. These are simplicial complexes that carry the information on the intersection patterns of a family of convex sets in R^d. We…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3164:field_when:0:193
SUMMARY:Classification results in equivariant symplectic geometry
DTSTART:2020-12-20T10:00:00
DTEND:2020-12-20T11:00:00
DSCRIPTION:Speaker: Yael Karshon, University of Toronto\n
Abstract:
I will report on some old and new classification results in
equivariant symplectic geometry, including my classification, joint with
Sue Tolman, of Hamiltonian torus actions with two dimensional quotients.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3162:field_when:0:194
SUMMARY:Phase retrieval stability via notions of graph connectivity
DTSTART:2020-12-16T13:00:00
DTEND:2020-12-16T14:00:00
DSCRIPTION:Speaker: Nadav Dym (Duke University)\n
Abstract:
Phase retrieval is the inverse problem of reconstructing a signal from linear measurements, when the phase of the measurements is lost and only the magnitude is known. This problem occurs in many applications including crystallography, optics, and acoustics.
In the talk I will discuss results on invertibility and stability of phase retrieval. I will focus on a recent paradigm which characterizes phase retrieval stability via appropriate notions of graph connectivity, and in…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3163:field_when:0:195
SUMMARY:S spaces and L spaces, part 1
DTSTART:2020-12-16T12:00:00
DTEND:2020-12-16T14:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
An S-space is a regular topological space that is hereditarily separable but not Lindel\"of. An L-space is a regular topological space that is hereditarily Lindel\"of but not separable. We will survey the history behind the question of their existence and present some constructions
END:VEVENT
BEGIN:VEVENT
UID:calendar:3158:field_when:0:196
SUMMARY:Rationality of representation zeta functions of compact p-adic analytic groups
DTSTART:2020-12-16T09:00:00
DTEND:2020-12-16T10:00:00
DSCRIPTION:Speaker: Prof. Alexander Stasinski (University of Durham)\n
Abstract:
A representation zeta function of a group G is a (meromorphic continuation of) a Dirichlet series in a complex variable s whose n-th coefficient is the number of irreducible representations of dimension n of G (supposing that these numbers are finite). In 2006 Jaikin-Zapirain proved one of the most fundamental results in the area, namely that if G is a FAb compact p-adic analytic group (e.g., SL_n(Z_p)) and p > 2, then the representation zeta function of G is "virtually rational"…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3156:field_when:0:197
SUMMARY:The Worpitzky identity for the groups of signed and even-signed permutations
DTSTART:2020-12-06T12:00:00
DTEND:2020-12-06T13:30:00
DSCRIPTION:Speaker: Eli Bagno (Jerusalem College of Technology)\n
Abstract:
The well-known Worpitzky identity provides a connection between two bases of : The standard basis and the binomial basis , where the Eulerian numbers for the Coxeter group of type (the symmetric group) serve as the entries of the transformation matrix.
Brenti has generalized this identity to the Coxeter groups of types and (signed and even-signed permutations groups, respectively) using generatingfunctionology.
Motivated by Foata-Schützenberger and Rawlings' proof for the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3157:field_when:0:198
SUMMARY:Model Theoretic Classification and its Applications to Algebra
DTSTART:2020-12-06T10:00:00
DTEND:2020-12-06T11:00:00
DSCRIPTION:Speaker: Yatir Halevi (Ben Gurion University)\n
Abstract:
Classification theory is a program initiated by Shelah in the early 70s with the aim of classifying complete first order theories into "tame" and "wild" theories by some relatively simple combinatorial invariants. Examples of such theories are stable, dependent and simple theories.
From the beginning, the applications stemming from this work moved in two intertwining directions.
The first, a detailed study of the geometry arising in such theories and applying these notions to…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3155:field_when:0:199
SUMMARY:Woodin Extender Algebra and its applications for absoluteness, part 2
DTSTART:2020-12-02T12:00:00
DTEND:2020-12-02T14:00:00
DSCRIPTION:Speaker: Menachem Magidor (HUJI)\n
Abstract:
we continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3148:field_when:0:200
SUMMARY:A freeness criterion without patching for modules over local rings
DTSTART:2020-12-02T08:30:00
DTEND:2020-12-02T09:30:00
DSCRIPTION:Speaker: Dr. Sylvain Brochard (Montpellier)\n
Abstract:
Let A->B be a local homomorphism of (commutative) Noetherian local rings. Bart de Smit conjectured in the late 1990's that if A and B have the same embedding dimension, then any finitely generated B-module that is flat over A, is flat over B. This conjecture was proved in 2017 and allows one in some situations to dispense with patching in the techniques à la Wiles to prove modularity lifting theorems (e.g. in the proof of FLT). We generalize this result as follows: if M is a…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3150:field_when:0:201
SUMMARY:Random permutations sampled by surface groups
DTSTART:2020-11-29T12:00:00
DTEND:2020-11-29T13:30:00
DSCRIPTION:Speaker: Doron Puder (Tel-Aviv University)\n
Abstract:
Let be the fundamental group of the closed orientable surface of genus , namely, . Fix an element and let be a uniformly random homomorphism to the symmetric group .
We develop new techniques to study the random permutation , and derive several results which are analogous to well-known results when is replaced with a free group.
This is joint work with Michael Magee.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3149:field_when:0:202
SUMMARY:Pattern Statistics in Permutations and Words
DTSTART:2020-11-29T10:00:00
DTEND:2020-11-29T11:00:00
DSCRIPTION:Speaker: Chaim Even-Zohar (The Alan Turing Institute, London)\n
Abstract:
Patterns in a large combinatorial structure, such as a graph, a word, or a permutation, are the induced substructures on small subsets of vertices or entries. If a permutation describes the relation between the y-ranks and x-ranks of n points in the xy-plane, then every subset of k points induces one of k! possible patterns. Similarly, in an n-letter word over a finite alphabet, every k positions induce a k-letter subword. Some important questions are: How frequently does each pattern…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3147:field_when:0:203
SUMMARY:Woodin Extender Algebra and its applications for absoluteness, part 1
DTSTART:2020-11-25T12:00:00
DTEND:2020-11-25T14:00:00
DSCRIPTION:Speaker: Menachem Magidor (HUJI)\n
Abstract:
This talk will survey known results and will be the first of several talks which will not necessarily follow in the consecutive weeks.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3145:field_when:0:204
SUMMARY:Generalized permutations related to degenerate Eulerian numbers
DTSTART:2020-11-22T12:00:00
DTEND:2020-11-22T13:30:00
DSCRIPTION:Speaker: Orli Herscovici (University of Haifa)\n
Abstract:
Carlitz (1979) defined degenerate Eulerian polynomials and numbers; however, there is no publication describing their combinatorial aspects.
In this talk we consider a combinatorial model that generalizes the standard definition of permutations and provides missing combinatorial proofs for some relations on degenerate Eulerian numbers…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3142:field_when:0:205
SUMMARY:Existence of Equilibrium in Repeated Blackwell Games when the Payoff is Tail Measurable
DTSTART:2020-11-22T10:00:00
DTEND:2020-11-22T11:00:00
DSCRIPTION:Speaker: Galit Ashkenazi-Golan\n
Abstract:
We prove the existence of equilibrium in repeated Blackwell games with Borel tail-measurable winning sets, and with Borel tail-measurable payoffs. The proof uses a regularity result of the minmax value
END:VEVENT
BEGIN:VEVENT
UID:calendar:3141:field_when:0:206
SUMMARY:Estimation of Manifolds from Point Clouds: Building Models from Data
DTSTART:2020-11-18T14:00:00
DTEND:2020-11-18T15:00:00
DSCRIPTION:Speaker: Barak Sober (Duke University)\n
Abstract:
A common observation in data-driven applications is that high dimensional data has a low intrinsic dimension, at least locally. Thus, when one wishes to work with data that is not governed by a clear set of equations, but still wishes to perform statistical or other scientific analysis, an optional model is the assumption of an underlying manifold from which the data was sampled. This manifold, however, is not given explicitly but we can obtain samples of it (i.e., the individual data…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3144:field_when:0:207
SUMMARY:Independent families in the countable and the uncountable
DTSTART:2020-11-18T12:00:00
DTEND:2020-11-18T14:00:00
DSCRIPTION:Speaker: Vera Fischer (Vienna)\n
Abstract:
Independent families on $\omega$ are families of infinite sets of integers with the property that for any two finite subfamilies $A$ and $B$ the set $\bigcap A\backslash \bigcup B$ is infinite. Of particular interest are the sets of the possible cardinalities of maximal independent families, which we refer to as the spectrum of independence. Even though we do have the tools to control the spectrum of independence at $\omega$ (at least to a large extent), there are many relevant…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3135:field_when:0:208
SUMMARY:The congruence kernel problem for endomorphism rings
DTSTART:2020-11-18T08:30:00
DTEND:2020-11-18T09:30:00
DSCRIPTION:Speaker: Tamar Bar-On (Bar-Ilan University)\n
Abstract:
We present the congruence kernel problem for endomorphism rings of finitely generated projective modules, and give it a positive answer in the case of faithful modules over commutative rings.
=================================================
Michael Schein is inviting you to a scheduled Zoom meeting.
Topic: Bar-Ilan Algebra Seminar -- Bar-On
Time: Nov 18, 2020 10:30 AM Jerusalem
Join Zoom Meeting
https://us02web.zoom.us/j/88355947298?pwd=bFZvU2xqand4dXdEaDNoUnBJdHVUd…
Meeting ID…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3139:field_when:0:209
SUMMARY:The resonance arrangement
DTSTART:2020-11-15T12:00:00
DTEND:2020-11-15T13:30:00
DSCRIPTION:Speaker: Lukas Kühne (Max Planck Institute, Leipzig)\n
Abstract:
The resonance arrangement is the arrangement of hyperplanes which has all nonzero 0/1-vectors in R^n as normal vectors. It is also called the all-subsets arrangement. Its chambers appear in algebraic geometry, in mathematical physics, and as maximal unbalanced families in economics.
In this talk, I will present a universality result of the resonance arrangement. Subsequently, I will report on partial progress on counting its chambers. Along the way, I will review some basics of the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3138:field_when:0:210
SUMMARY:Stationary random entire functions and related questions
DTSTART:2020-11-11T14:00:00
DTEND:2020-11-11T15:00:00
DSCRIPTION:Speaker: Adi Glucksam (University of Toronto)\n
Abstract:
Let T be the action of the complex plane on the space of entire functions defined by translations, i.e T_w takes the entire function f(z) to the entire function f(z+w). B.Weiss showed in `97 that there exists a probability measure defined on the space of entire functions, which is invariant under this action. In this talk I will present optimal bounds on the minimal possible growth of functions in the support of such measures, and discuss other growth related problems inspired by this…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3143:field_when:0:211
SUMMARY:Higher Chang Conjecture, part 2
DTSTART:2020-11-11T12:00:00
DTEND:2020-11-11T14:00:00
DSCRIPTION:Speaker: Yait Hayut (HUJI)\n
Abstract:
Here is the recording
END:VEVENT
BEGIN:VEVENT
UID:calendar:3136:field_when:0:212
SUMMARY:Construction of quasi-morphisms on groups of measure-preserving homeomorphisms of non-orientable surfaces
DTSTART:2020-11-10T09:30:00
DTEND:2020-11-10T10:30:00
DSCRIPTION:Speaker: Rishi Kumar, BGU\n
Abstract:
A quasi-morphism on a group G is a real-valued function which satisfies the homomorphism equation up to a bounded error. Let Ng be a non-orientable surface of genus g≥ 3 and let Homeo0(Ng,μ) be the identity component of the group of measure-preserving homeomorphisms of Ng.
We prove that the space of homogeneous quasi-morphisms on the group Homeo0(Ng,μ) is infinite-dimensional. This project is part of an M.Sc. thesis under the supervision of Dr. Brandenbursky.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3133:field_when:0:213
SUMMARY:An identity of permutation statistics on the hyperoctahedral group
DTSTART:2020-11-08T12:00:00
DTEND:2020-11-08T13:30:00
DSCRIPTION:Speaker: Michael Schein (Bar-Ilan University)\n
Abstract:
We define a statistic on the hyperoctahedral group B_n; this is a special case of one introduced by Stembridge and Waugh. We show that a certain two-variable generating function involving this statistic factors into the product of a generating function over the symmetric group S_n and some simple binomials. Then we mention related results by Macdonald and Carnevale-Shechter-Voll, and discuss what the correct way to state and prove our identity should be.
Our motivation for this…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3134:field_when:0:214
SUMMARY:Rough walks
DTSTART:2020-11-08T10:00:00
DTEND:2020-11-08T11:00:00
DSCRIPTION:Speaker: Tal Orenshtein (Technical University of Berlin and Weierstrass Institute)\n
Abstract:
Random walks in random environment (RWRE) have been extensively studied in the last half-century. Two prototypical cases are the reversible and the ballistic classes and even though they are fundamentally different, functional central limit theorems (FCLT) are known to hold in both. This is done using rather different techniques; Kipnis-Varadhan's theory for additive functional of Markov processes is applicable in the reversible case while for the ballistic class the main feature is a…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3131:field_when:0:215
SUMMARY:Lie superalgebras, an introductory talk
DTSTART:2020-11-04T16:30:00
DTEND:2020-11-04T17:30:00
DSCRIPTION:Speaker: Maria Gorelik, WIS\n
Abstract:
This is the first lecture of STARS (Superalgebra Theory and Representations Seminar) series.
Meeting ID: 919 8455 8186
Password: 663945https://weizmann.zoom.us/j/91984558186?pwd=dzl2Z2hPRWtzaDF6R1pySXd4OGFIQT09
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BEGIN:VEVENT
UID:calendar:3130:field_when:0:216
SUMMARY:Recent Progress on the Exact Overlaps Conjecture
DTSTART:2020-11-04T14:00:00
DTEND:2020-11-04T15:00:00
DSCRIPTION:Speaker: Ariel Rapaport (University of Cambridge)\n
Abstract:
A well known conjecture in fractal geometry says that the dimension of a self-similar measure is strictly smaller than its natural upper bound only in the presence of exact overlaps. That is, only if the maps in the generating iterated function system do not generate a free semigroup. I will present recent developments regarding this conjecture, focusing on my joint work with P. Varjú regarding homogeneous systems of three maps
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BEGIN:VEVENT
UID:calendar:3132:field_when:0:217
SUMMARY:Higher Chang Conjecture
DTSTART:2020-11-04T12:00:00
DTEND:2020-11-04T14:00:00
DSCRIPTION:Speaker: Yait Hayut (HUJI)\n
Abstract:
In this talk I will present some results regarding the consistency strength of Higher variants of Chang's Conjecture.
I will start with the classical result by Silver of Chang's Conjecture from $\omega_1$-Erdos cardinal.
Then, I will give an upper bound for the consistency strength of $(\aleph_{\omega+1}, \aleph_{\omega}) -->>(\aleph_1, \aleph_0)$
and $(\aleph_4, \aleph_3) -->> (\aleph_2, \aleph_1)$ (joint with Eskew)
from supercompactness assumptions.
If time…
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BEGIN:VEVENT
UID:calendar:3127:field_when:0:218
SUMMARY:Automorphism groups, elliptic curves, and the PORC conjecture
DTSTART:2020-11-04T08:30:00
DTEND:2020-11-04T09:30:00
DSCRIPTION:Speaker: Dr. Mima Stanojkovski (Leipzig)\n
Abstract:
In 1960, Graham Higman formulated his famous PORC conjecture in relation to the function f(p,n) counting the isomorphism classes of p-groups of order p^n . By means of explicit formulas, the PORC conjecture has been verified for n < 8. Despite that, it is still open and has in recent years been questioned. I will discuss (generalizations of) an example of du Sautoy and Vaughan-Lee (2012), together with a conceptualization of the phenomena they observe. Hidden heroes of this story…
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BEGIN:VEVENT
UID:calendar:3129:field_when:0:219
SUMMARY:From fractional to integral matchings in d-partite hypergraphs
DTSTART:2020-11-01T12:00:00
DTEND:2020-11-01T13:30:00
DSCRIPTION:Speaker: Erel Segal-Halevi (Ariel University)\n
Abstract:
A d-partite hypergraph is called *fractionally balanced* if there exists a non-negative function on its edge set that has constant degrees in each vertex side. Using a topological version of Hall's theorem, we prove new lower bounds on the matching number of such hypergraphs. Our bounds yield results on envy-free division of multiple cakes, covering colorful families of d-intervals, and rental harmony with multiple houses.
Joint work with Ron Aharoni, Eli Berger, Joseph Briggs and…
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BEGIN:VEVENT
UID:calendar:3128:field_when:0:220
SUMMARY:On Continuous Tree-Like Scales and related properties of Internally Approachable structures
DTSTART:2020-10-28T12:00:00
DTEND:2020-10-28T14:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
In his PhD thesis, Luis Pereira isolated and developed several principles of singular cardinals that emerge from Shelah's PCF theory; principles which involve properties of scales, such as the inexistence of continuous Tree-Like scales, and properties of internally approachable structures such as the Approachable Free Subset Property.
In the talk, we will discuss these principles and their relations, and present new results from a joint work with Dominik Adolf concerning their…
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BEGIN:VEVENT
UID:calendar:3123:field_when:0:221
SUMMARY:Generalized Brauer dimension and other arithmetic invariants of semi-global fields
DTSTART:2020-10-28T08:30:00
DTEND:2020-10-28T09:30:00
DSCRIPTION:Speaker: Dr. Saurabh Gosavi (Bar-Ilan University)\n
Abstract:
Given a finite set of Brauer classes B of a fixed period \ell, we define eind(B) to be the minimum of degrees of field extensions L/F such that b \otimes_F L = 0 for every b in B. We provide upper bounds for eind(B) which depend on invariants of fields of lower arithmetic complexity, for B in the Brauer group of a semi-global field. As a simple application of our result, we obtain an upper bound for the splitting index of quadratic forms and finiteness of symbol length for function…
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BEGIN:VEVENT
UID:calendar:3124:field_when:0:222
SUMMARY:Algebraic Structures on Automorphic L-Functions
DTSTART:2020-10-27T09:30:00
DTEND:2020-10-27T10:30:00
DSCRIPTION:Speaker: Gal Dor\n
Abstract:
Consider the function field F of a smooth curve over F_q, with q > 2.
L-functions of automorphic representations of GL(2) over F are important objects for studying the arithmetic properties of the field F. Unfortunately, they can be defined in two different ways: one by Godement-Jacquet, and one by Jacquet-Langlands. Classically, one shows that the resulting L-functions coincide using a complicated computation.
I will present a conceptual proof that the two families coincide…
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BEGIN:VEVENT
UID:calendar:3125:field_when:0:223
SUMMARY:On the Stanley-Wilf limit of the pattern 1324
DTSTART:2020-10-25T12:00:00
DTEND:2020-10-25T13:30:00
DSCRIPTION:Speaker: Toufik Mansour (University of Haifa)\n
Abstract:
We present an explicit formula for the generating function for the number of permutations of length $n$ that avoid $1324$, in terms of generating functions for permutations that have a kernel shape of length $m$, $m \ge 2$. This allows us to write down a systematic procedure for finding a lower bound for approximating the Stanley-Wilf limit of the pattern $1324$.
Joint work with Christian Nassau.
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BEGIN:VEVENT
UID:calendar:3122:field_when:0:224
SUMMARY:Operator algebraic graph theory
DTSTART:2020-10-25T10:00:00
DTEND:2020-10-25T11:00:00
DSCRIPTION:Speaker: Adam Dor On (University of Copenhagen)\n
Abstract:
The Toeplitz algebra of a directed graph is the norm-closed $*$-algebra generated by edge and vertex concatenation operators on the inner-product space of square summable sequences indexed by finite paths of the graph. A canonical quotient of it is the celebrated Cuntz-Krieger algebra, which is deeply connected to the associated subshift of finite type of the directed graph. Understanding representations of Cuntz-Krieger algebras has become useful for producing wavelet bases on self-…
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BEGIN:VEVENT
UID:calendar:3120:field_when:0:225
SUMMARY:Local club condensation in extender models
DTSTART:2020-10-22T07:00:00
DTEND:2020-10-22T09:00:00
DSCRIPTION:Speaker: Gabriel Fernandes (BIU)\n
Abstract:
Local club condensation is an abstraction of the condensation properties of the constructible hierarchy.
We will prove that for extender models that are countably iterable, given a cardinal kappa, the J_alpha^{E} hierarchy witnesses local club condensation in the interval (kappa^+,kappa^++) if and only if kappa is not a subcompact cardinal in L[E].
From the above and the equivalence between subcompact cardinals and square, due to Schimmerling and Zeman, it follows that in such…
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BEGIN:VEVENT
UID:calendar:3126:field_when:0:226
SUMMARY:Equidistribution of mesh patterns of length two and Kitaev and Zhang's conjectures
DTSTART:2020-10-18T11:00:00
DTEND:2020-10-18T12:30:00
DSCRIPTION:Speaker: Bin Han (Bar-Ilan University)\n
Abstract:
A systematic study of avoidance of mesh patterns of length 2 was conducted by Hilmarsson et al. in 2015. In a recent paper, Kitaev and Zhang examined the distribution of the aforementioned patterns.
We show that two pairs of triple mesh patterns are equidistributed, by constructing two involutions on permutations. As an application we confirm four conjectures raised by Kitaev and Zhang recently.
Based on joint work with Jiang Zeng.
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BEGIN:VEVENT
UID:calendar:3121:field_when:0:227
SUMMARY:Triples and systems: a general algebraic structure theory applicable to tropical mathematics
DTSTART:2020-10-18T09:00:00
DTEND:2020-10-18T10:00:00
DSCRIPTION:Speaker: Louis Rowen (Bar-Ilan University)\n
Abstract:
Our goal is to present an axiomatic algebraic theory which unifies
and “explains” aspects of tropical algebra, hyperfields, and fuzzy rings in terms
of classical algebraic concepts, especially negation, which may not exist a priori.
It was motivated by an attempt to understand whether or not it is coincidental
that basic algebraic theorems are mirrored in supertropical algebra, and was
spurred by the realization that some of the same results are obtained in parallel
research on…
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UID:calendar:3118:field_when:0:228
SUMMARY:Coloring Superstable Graphs
DTSTART:2020-10-12T08:00:00
DTEND:2020-10-12T10:00:00
DSCRIPTION:Speaker: Yatir Halevi (BGU)\n
Abstract:
Given a graph G=(V,E), a coloring of G in \kappa colors is a map c:V\to \kappa in which adjacent vertices are colored in different colors. The chromatic number of G is the smallest such \kappa.
We will briefly review some questions and conjectures on the chromatic number of infinite graphs and will mainly concentrate on the following strong form of Taylor's conjecture:
If G is an infinite graph with chromatic number\geq \alepha_1 then it contains all finite subgraphs of Sh_n(\omega)…
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BEGIN:VEVENT
UID:calendar:3101:field_when:0:229
SUMMARY:On the inexistence of Continuous Tree-Like Scales, and the Approachable Free Subset Property
DTSTART:2020-09-14T08:00:00
DTEND:2020-09-14T10:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
In his PhD thesis, Luis Pereira has isolated two properties of sequences of regular cardinals (kappa_n)_n from Shelah's PCF theory, which are related to the possible consistency of 2^{aleph_omega} being greater or equal to aleph_{omega_1}, when aleph_omega is a strong limit cardinal.
The first property is the inexistence of a continuous tree-like scale on the product of regular cardinals kappa_n, n < omega. A scale <f_alpha : alpha < lambda> is said to be tree-like if for…
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BEGIN:VEVENT
UID:calendar:3100:field_when:0:230
SUMMARY:Jensen's covering theorem for L
DTSTART:2020-08-31T08:00:00
DTEND:2020-08-31T10:00:00
DSCRIPTION:Speaker: Gabriel Fernandes (BIU)\n
Abstract:
Jensen's covering theorem for Godel's constructible universe, L, says that if there is no non-trivial elementary embedding from L into L, then for every uncountable set of ordinals, X, there is a set, Y, such that Y is an element of L, |X| = |Y| and X is a subset of Y.
We will sketch the proof of the covering lemma for L.
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BEGIN:VEVENT
UID:calendar:3099:field_when:0:231
SUMMARY:Weak diamond, Uniformization and its connection to Whitehead's problem
DTSTART:2020-08-26T08:00:00
DTEND:2020-08-26T10:00:00
DSCRIPTION:Speaker: Menachem Magidor (HUJI)\n
Abstract:
I'll speak and I'll present some old results about weak diamond, uniformization and maybe some connections to Whitehead problem. In particular I'll present Woodin's elegant proof to the Devlin-Shelah equivalence of Weak diamond with 2^\aleph_0<2^\aleph_1.
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BEGIN:VEVENT
UID:calendar:3096:field_when:0:232
SUMMARY:Explicit Serre weights for two-dimensional Galois representations
DTSTART:2020-08-26T07:30:00
DTEND:2020-08-26T08:30:00
DSCRIPTION:Speaker: Dr. Misja Steinmetz (Leiden University)\n
Abstract:
The Serre weight conjectures are conjectures that, roughly
speaking, predict the weight of a modular form from which a given mod p
Galois representation arises. Starting from Serre's original conjecture
for classical modular forms, I will give a motivated approach towards
correct generalisations of the Serre weight conjectures to Hilbert
modular forms. Then I'll talk about new results giving a more explicit
version of the weight conjectures for Hilbert modular forms…
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UID:calendar:3098:field_when:0:233
SUMMARY:Square of Menger groups
DTSTART:2020-08-24T08:00:00
DTEND:2020-08-24T10:00:00
DSCRIPTION:Speaker: Jialiang He (BIU)\n
Abstract:
This work is cooperated with Yinhe Peng and Liuzhen Wu.
I will present a few constructions for square of Menger group problem in metrizable sense and generally sense in this talk.
Under cov(M)=c, for any n\geq 1, there is a subgroup G of Z^N such that G^n is Menger but G^{n+1} is not Menger.
Under cov(M)=d=cf(d)$, for any n\geq 1, there is a subgroup G of R such that G^n is Menger but G^{n+1} is not Menger.
For any n\geq 1, There is a Menger subgroup G of R^{\…
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UID:calendar:3097:field_when:0:234
SUMMARY:Coding well ordering of the reals with ladders, part 5
DTSTART:2020-08-19T08:00:00
DTEND:2020-08-19T10:00:00
DSCRIPTION:Speaker: Uri Abraham (BGU) \n
Abstract:
we continue
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BEGIN:VEVENT
UID:calendar:3010:field_when:0:235
SUMMARY:Non-admissible modulo p representations of GL_2(Q_{p^2})
DTSTART:2020-08-19T07:30:00
DTEND:2020-08-19T08:30:00
DSCRIPTION:Speaker: Prof. Eknath Ghate (Tata Institute of Fundamental Research, Mumbai)\n
Abstract:
The notion of admissibility of representations of p-adic groups
goes back to Harish-Chandra. Jacquet and Vigneras have shown that
smooth irreducible representations of connected reductive p-adic
groups over algebraically closed fields of characteristic different
from p are admissible.
The smooth irreducible representations of $\mathrm{GL}_2({\mathbb Q}_p)$
over $\bar{\mathbb F}_p$ are also known to be admissible, by the
work of Barthel-Livne, Breuil and…
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BEGIN:VEVENT
UID:calendar:3094:field_when:0:236
SUMMARY:Fedorchuck's space, part 2
DTSTART:2020-08-17T08:00:00
DTEND:2020-08-17T10:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
we continue
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BEGIN:VEVENT
UID:calendar:3093:field_when:0:237
SUMMARY:Coding well ordering of the reals with ladders, part 4
DTSTART:2020-08-12T08:00:00
DTEND:2020-08-12T10:00:00
DSCRIPTION:Speaker: Uri Abraham (BGU) \n
Abstract:
we continue
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BEGIN:VEVENT
UID:calendar:3092:field_when:0:238
SUMMARY:Chang's conjecture, part 2
DTSTART:2020-08-10T08:00:00
DTEND:2020-08-10T10:00:00
DSCRIPTION:Speaker: Jing Zhang (BIU)\n
Abstract:
we continue
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BEGIN:VEVENT
UID:calendar:3012:field_when:0:239
SUMMARY:Coding well ordering of the reals with ladders, part 3
DTSTART:2020-08-05T08:00:00
DTEND:2020-08-05T10:00:00
DSCRIPTION:Speaker: Uri Abraham (BGU) \n
Abstract:
we continue
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BEGIN:VEVENT
UID:calendar:3091:field_when:0:240
SUMMARY:Chang's conjecture, part 1
DTSTART:2020-08-03T08:00:00
DTEND:2020-08-03T10:00:00
DSCRIPTION:Speaker: Jing Zhang (BIU)\n
Abstract:
We'll talk about colorings of triples of w2
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BEGIN:VEVENT
UID:calendar:3009:field_when:0:241
SUMMARY:Fedorchuck's space, part 1
DTSTART:2020-07-27T08:00:00
DTEND:2020-07-27T10:00:00
DSCRIPTION:Speaker: Roy Shalev\n
Abstract:
We shall present Fedorchuck's construction of a compact S-space of size 2^{w1}. If time permits, we shall show how it connects with the Moore-Mrowka problem.
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BEGIN:VEVENT
UID:calendar:3007:field_when:0:242
SUMMARY:Coding well ordering of the reals with ladders, part 2
DTSTART:2020-07-22T08:00:00
DTEND:2020-07-22T10:00:00
DSCRIPTION:Speaker: Uri Abraham (BGU) \n
Abstract:
we continue
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BEGIN:VEVENT
UID:calendar:3008:field_when:0:243
SUMMARY:A Partition Theorem for Scattered Order Types, part 2
DTSTART:2020-07-20T08:00:00
DTEND:2020-07-20T10:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU) \n
Abstract:
we continue
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BEGIN:VEVENT
UID:calendar:3006:field_when:0:244
SUMMARY:Coding well ordering of the reals with ladders, part 1
DTSTART:2020-07-15T08:00:00
DTEND:2020-07-15T10:00:00
DSCRIPTION:Speaker: Uri Abraham (BGU)\n
Abstract:
Results from the 2002 paper "Coding with Ladders a Well Ordering of the Reals" by Abraham and Shelah.
Recoding is now available.
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BEGIN:VEVENT
UID:calendar:2999:field_when:0:245
SUMMARY:A Partition Theorem for Scattered Order Types, part 1
DTSTART:2020-07-13T08:00:00
DTEND:2020-07-13T10:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BIU)\n
Abstract:
I will talk about the titular paper by Komjath and Shelah. It is a short paper.
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BEGIN:VEVENT
UID:calendar:2996:field_when:0:246
SUMMARY:The tree property at Aleph_{w+1}
DTSTART:2020-07-01T08:00:00
DTEND:2020-07-01T10:00:00
DSCRIPTION:Speaker: Tzoor Plotnikov (HUJI)\n
Abstract:
Covering Neeman's proof
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BEGIN:VEVENT
UID:calendar:2995:field_when:0:247
SUMMARY:On the free subset number of a topological space and their G_\delta modification
DTSTART:2020-06-24T08:00:00
DTEND:2020-06-24T10:00:00
DSCRIPTION:Speaker: Istvan Juhasz (Renyi Institute)\n
Abstract:
Attached
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BEGIN:VEVENT
UID:calendar:2994:field_when:0:248
SUMMARY:Wide Aronszajn trees
DTSTART:2020-06-17T08:00:00
DTEND:2020-06-17T10:00:00
DSCRIPTION:Speaker: Mirna Dzamonja (UEA)\n
Abstract:
A wide Aronszajn tree is a tree is size and height omega_1 but with no uncountable branch. Such trees arise naturally in the study of model-theoretic notions on models of size aleph_1 as well as in generalised descriptive set theory. In their 1994 paper devoted to various aspects of such trees, Mekler and Väänänen studied the so called weak embeddings between such trees, which are simply defined as strict-order preserving functions. Their work raised the question if under MA there…
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BEGIN:VEVENT
UID:calendar:2993:field_when:0:249
SUMMARY:Tameness in Set Theory
DTSTART:2020-06-10T08:00:00
DTEND:2020-06-10T10:00:00
DSCRIPTION:Speaker: Matteo Viale (Torino)\n
Abstract:
We show that (assuming large cardinals) set theory is a tractable (and we dare to say tame) first order theory when formalized in a first order signature with natural predicate symbols for the basic definable concepts of second and third order arithmetic, and appealing to the model-theoretic notions of model completeness and model companionship.
Specifically we develop a general framework linking generic absoluteness results to model companionship and show that (with the required…
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BEGIN:VEVENT
UID:calendar:2939:field_when:0:250
SUMMARY:Prof. Nathalie Q. Balaban - TBA
DTSTART:2020-06-04T11:00:00
DTEND:2020-06-04T12:00:00
DSCRIPTION:Speaker: Prof. Nathalie Q. Balaban\n
Abstract:
TBA
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BEGIN:VEVENT
UID:calendar:2988:field_when:0:251
SUMMARY:BPFA and Delta_1-definablity of NS_{w1}
DTSTART:2020-06-03T08:00:00
DTEND:2020-06-03T10:00:00
DSCRIPTION:Speaker: Liuzhen Wu (Chinese Acad. Sciences, Beijing)\n
Abstract:
I will discuss a proof of the joint consistency of BPFA and \Delta_1-definablity of NS_{\omega_1}.
Joint work with Stefan Hoffelner and Ralf Schindler.
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BEGIN:VEVENT
UID:calendar:2987:field_when:0:252
SUMMARY:Filter Reflection
DTSTART:2020-05-27T08:00:00
DTEND:2020-05-27T10:00:00
DSCRIPTION:Speaker: Miguel Moreno (KGRC)\n
Abstract:
Filter reflection is an abstract version of stationary reflection. In this talk we will define filter reflection and different avatars of it. We will show the compatibility with large cardinals, forcing axioms, and V＝L.
We will focus on the case when filter reflection holds and stationary reflaction fails, we will discuss how to force this case.
We will also discuss the failure of filter reflection, how to force the failure and the requierements for it.
If the time allows, some…
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BEGIN:VEVENT
UID:calendar:2985:field_when:0:253
SUMMARY:Compactness problems for chromatic numbers of graphs
DTSTART:2020-05-20T08:00:00
DTEND:2020-05-20T10:00:00
DSCRIPTION:Speaker: Menachem Magidor (HUJI)\n
Abstract:
I'll speak about compactness problems for chromatic numbers of graphs. The main result will be a some what simplified proof of a theorem by Shelah, that a non reflecting stationary subset of a regular cardinal \lambda S\subseteq S^\lambda_kappa implies (under mild cardinal arithmetic assumptions) that there is a graph of size \lambda with chromatic number lambda , but every smaller cardinality subgraph has chromatic number <=kappa.
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BEGIN:VEVENT
UID:calendar:2984:field_when:0:254
SUMMARY:Sigma-Prikry forcing, part 2
DTSTART:2020-05-13T08:00:00
DTEND:2020-05-13T10:00:00
DSCRIPTION:Speaker: Alejandro Poveda (Universitat de Barcelona) \n
Abstract:
(joint work with A. Rinot and D. Sinapova)
In the previous talk, we introduced the notion of \Sigma-Prikry forcing and showed that many classical Prikry-type forcing which center on countable cofinalities fall into this framework.
The aim of this talk is to present our iteration scheme for \Sigma-Prikry forcings.
In case time permits, we will also show how to use this general iteration theorem to derive as a corollary the following strengthening of Sharon’s theorem: starting with…
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BEGIN:VEVENT
UID:calendar:2938:field_when:0:255
SUMMARY:Prof. Yachin Ivry - TBA
DTSTART:2020-05-07T11:00:00
DTEND:2020-05-07T12:00:00
DSCRIPTION:Speaker: Prof. Yachin Ivry\n
Abstract:
TBA
END:VEVENT
BEGIN:VEVENT
UID:calendar:2983:field_when:0:256
SUMMARY:Sigma-Prikry forcing, part 1
DTSTART:2020-05-06T08:00:00
DTEND:2020-05-06T10:00:00
DSCRIPTION:Speaker: Alejandro Poveda (Universitat de Barcelona)\n
Abstract:
In a joint project with A. Rinot and D. Sinapova we introduce a class of notions of forcing which we call $\Sigma$-Prikry, and show that many of the known Prikry-type notions of forcing that centers around singular cardinals of countable cofinality are $\Sigma$-Prikry. Among these examples one may find Prikry forcing and its supercompact version, Gitik-Sharon forcing or the Extender Based Prikry forcing due to Gitik and Magidor. Our first result shows that there is a functor $\mathbb{…
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BEGIN:VEVENT
UID:calendar:2974:field_when:0:257
SUMMARY:Transformations of the transfinite plane
DTSTART:2020-04-22T08:00:00
DTEND:2020-04-22T10:00:00
DSCRIPTION:Speaker: Jing Zhang (BIU)\n
Abstract:
We discuss the existence of certain transformation functions turning pairs of ordinals into triples (or pairs) of ordinals, that allows reductions of complicated Ramsey theoretic problems into simpler ones. We will focus on the existence of various kinds of strong colorings. The basic technique is Todorcevic's walks on ordinals. Joint work with Assaf Rinot.
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BEGIN:VEVENT
UID:calendar:2982:field_when:0:258
SUMMARY:Borel determinacy can not be proved in Zermelo Set Theoy
DTSTART:2020-04-01T08:00:00
DTEND:2020-04-01T10:00:00
DSCRIPTION:Speaker: Menachem Magidor (HUJI)\n
Abstract:
I'll speak about the Friedman-Martin theorem that Borel determinacy can not be proved in Zermelo Set Theoy. (Namely, one needs reflection for getting it).
Recoding is now available.
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