BEGIN:VCALENDAR
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X-WR-CALNAME;VALUE=TEXT:סמינרים | המחלקה למתמטיקה
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BEGIN:VEVENT
UID:calendar:3708:field_when:0:0
SUMMARY:Traces of powers of random p-adic matrices
DTSTART:2024-11-06T08:30:00
DTEND:2024-11-06T09:30:00
DSCRIPTION:Speaker: Noam Pirani (Tel Aviv University)\n
Abstract:
What is the distribution of the traces of powers of a random matrix? A classical result of Diaconis and Shahshahani states that the traces tr(M^i) for a random unitary matrix M are independent and identically distributed (i.i.d.) complex Gaussians. Recently, Gorodetsky and Rodgers proved that the traces of powers of random unitary matrices over F_q are i.i.d. uniform random variables in F_q. In this talk, we will discuss the distribution of traces of powers of random p-adic matrices…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3707:field_when:0:1
SUMMARY:The decidability of Krohn-Rhodes complexity for all finite semigroups
DTSTART:2024-10-30T08:30:00
DTEND:2024-10-30T09:30:00
DSCRIPTION:Speaker: Stuart Margolis (Bar-Ilan University)\n
Abstract:
The Krohn-Rhodes Theorem shows that every finite semigroup S divides, that is, is a quotient of a subsemigroup of a wreath product of simple groups that are Jordan-Holder factors of the subgroups of S and the 3-element monoid U consisting of two right-zeroes and an identity element. We call a finite semigroup prime if whenever it divides a wreath product of two finite semigroups then it divides one of the factors. Then the Krohn-Rhodes Theorem also shows that a semigroup is…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3702:field_when:0:2
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 9
DTSTART:2024-10-21T13:00:16
DTEND:2024-10-21T15:00:18
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
We prove that the conclusion of Theorem A from our preprint holds true also for mu an ineffable cardinal. In particular, for every regular uncountable cardinal mu, if there is a special Aronszajn tree of height mu^+, then there is one satisfying a very strong negative partition relation.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3701:field_when:0:3
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 8
DTSTART:2024-10-14T11:00:00
DTEND:2024-10-14T13:00:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
We prove that for every strongly inaccessible cardinal lambda, any basis for the class of special lambda^+-Aronszajn lines must have size at least lambda.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3700:field_when:0:4
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 7
DTSTART:2024-10-10T11:00:00
DTEND:2024-10-10T13:00:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
We prove that for every regular uncountable cardinal lambda, if there exists a lambda^+-Aronszajn line, then there exists one with no lambda^+-Countryman subline. We have already seen the proof for the case that is lambda is non-ineffable. Today, we shall give a separate proof for ineffables.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3699:field_when:0:5
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 6
DTSTART:2024-09-30T07:00:00
DTEND:2024-09-30T08:59:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
Let lambda be a regular uncountable cardinal that is non-ineffable, and consider the class C of all special lambda^+-Aronszajn trees ordered by the relation of weak embeddability. We shall prove that the if above class is nonempty then it moreover contains a copy of (lambda^+,\subseteq).
END:VEVENT
BEGIN:VEVENT
UID:calendar:3698:field_when:0:6
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 5
DTSTART:2024-09-16T05:00:00
DTEND:2024-09-16T07:00:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
We complete the proof that if there exists an w2-Aronszajn line, then there exists one that contains no w2-Countryman line. This provides a negative answer to a question of Justin Moore
END:VEVENT
BEGIN:VEVENT
UID:calendar:3696:field_when:0:7
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 4
DTSTART:2024-09-12T11:00:00
DTEND:2024-09-12T13:00:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3691:field_when:0:8
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 3
DTSTART:2024-09-05T09:00:02
DTEND:2024-09-05T09:04:00
DSCRIPTION:Speaker: Tanmay Inamdar (BGU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3690:field_when:0:9
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 2
DTSTART:2024-08-29T11:00:00
DTEND:2024-08-29T13:00:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3686:field_when:0:10
SUMMARY:Anti-basis theorems for higher Aronszajn lines, part 1
DTSTART:2024-08-15T13:00:00
DTEND:2024-08-15T15:00:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
Aronszajn (1935) proved that there exists a special w1-Aronszajn tree and Jensen (1972) proved that, more generally, the existence of a special (mu^+)-Aronszajn tree is equivalent to the weak square principle holding at mu. We shall present a far-reaching extension of Jensen's theorem. As an application, we get that if there exists a special w2-Aronszajn tree, then any basis for the class of w2-Aronszajn lines must be of the maximal possible size 2^{w2}. This is in contrast with…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3681:field_when:0:11
SUMMARY:Rudin's Dowker space revisited
DTSTART:2024-07-22T08:00:00
DTEND:2024-07-22T10:00:00
DSCRIPTION:Speaker: Menachem Kojman (BGU)\n
Abstract:
TBA
END:VEVENT
BEGIN:VEVENT
UID:calendar:3676:field_when:0:12
SUMMARY:The elegance of the component tableaux in type A
DTSTART:2024-07-17T07:30:00
DTEND:2024-07-17T08:30:00
DSCRIPTION:Speaker: Yasmine Fittouhi (Weizmann Institute of Science)\n
Abstract:
Let $G$ be a simple algebraic group over the complex field $\mathbb C$, $B$ a fixed Borel subgroup, $P$ a parabolic subgroup containing $B$, $P'$ its derived group and $\mathfrak m$ the Lie algebra of its nilradical.
The nilfibre $\mathscr N$ for this action is the zero locus of the augmentation $\mathscr I_+$ of the semi-invariant algebra $\mathscr I:=\mathbb C[\mathfrak m]^{P'}$.
In this discussion, we focus on the study of $\mathscr N$ for $G=SL(n)$. …
END:VEVENT
BEGIN:VEVENT
UID:calendar:3677:field_when:0:13
SUMMARY:Algebraic structures based on graph contraction
DTSTART:2024-07-14T11:05:00
DTEND:2024-07-14T12:30:00
DSCRIPTION:Speaker: Anton Khoroshkin (U Haifa)\n
Abstract:
In this talk, I will introduce a new algebraic structure called "contractad" resembling the contraction of a subgraph in a simple connected graph.
Examples of contractads include Hamiltonian paths, spanning trees, and configuration spaces.
These examples admit presentations with quadratic relations and standard methods of homological algebra may help us to get functional equations for generating series.
As an application, I will show a simple generating series counting…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3674:field_when:0:14
SUMMARY:Invariants of non-isolated singularities of hypersurfaces
DTSTART:2024-07-10T07:30:00
DTEND:2024-07-10T08:30:00
DSCRIPTION:Speaker: Yotam Svoray (University of Utah)\n
Abstract:
A key tool in understanding (complex analytic) hypersurface singularities is to study what properties are preserved under special deformations. For example, the relationship between the Milnor number of an isolated singularity and the number of A_1 points. In this talk we will discuss the transversal discriminant of a singular hypersurface whose singular locus is a smooth curve, and how it can be applied in order to generalize a classical result by Siersma, Pellikaan, and de Jong…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3675:field_when:0:15
SUMMARY:Eight times four bialgebras of hypergraphs, cointeractions, and chromatic polynomials
DTSTART:2024-07-07T11:05:00
DTEND:2024-07-07T12:30:00
DSCRIPTION:Speaker: Gunnar Fløystad (U Bergen)\n
Abstract:
Link to the recording
The bialgebra of hypergraphs is shown to have a cointeracting bialgebra structure.
We show that the associated polynomial is the hypergraph chromatic polynomial.
Moreover, hypergraphs occur in quartets: there is a dual, a complement, and a dual complement hypergraph.
These correspondences are involutions and give rise to three other double bialgebras, and three more chromatic polynomials.
In all we give eight…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3670:field_when:0:16
SUMMARY:Can group laws be learned using random walks?
DTSTART:2024-07-03T07:30:00
DTEND:2024-07-03T08:30:00
DSCRIPTION:Speaker: Gil Goffer (University of California, San Diego)\n
Abstract:
In various cases, a law that holds in a group with high probability must actually hold for all elements. For instance, a finite group in which the commutator law [x,y]=1 holds with probability larger than 5/8 must be abelian. In the talk I’ll discuss a probabilistic approach to laws on infinite groups, using random walks, and present results, joint with Be’eri Greenfeld, answering a few questions of Amir, Blachar, Gerasimova, and Kozma.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3671:field_when:0:17
SUMMARY:Aldous-type spectral gap results for the complete monomial group
DTSTART:2024-06-30T11:05:00
DTEND:2024-06-30T12:30:00
DSCRIPTION:Speaker: Subhajit Ghosh (IIT, Madras)\n
Abstract:
Link to the recording
We consider the continuous-time random walk on $G\wr S_n$, the complete
monomial group of degree $n$ over a finite group $G$.
An analogue of the Aldous' spectral gap conjecture is presented and proved.
For more details, see enclosed file.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3669:field_when:0:18
SUMMARY:Forcing with side conditions to kill club guessing at w2
DTSTART:2024-06-27T13:00:00
DTEND:2024-06-27T15:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We discuss generalizations to w2 of Moore's principle Mho and prove the consistency of the failure of one of them. This answers a question of Inamdar and Rinot.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3665:field_when:0:19
SUMMARY:Combinatorial methods to investigate the length of algebras
DTSTART:2024-06-23T11:05:00
DTEND:2024-06-23T12:30:00
DSCRIPTION:Speaker: Alexander Guterman (BIU)\n
Abstract:
Link to the recording
An important combinatorial characteristic of finite-dimensional algebras is their length. The length of a finite system of generators for a finite-dimensional
algebra over a field is the least positive integer $k$, such that the products of generators of length not exceeding $k$ span this algebra as a vector space.
The maximum length over all systems of generators of an algebra is called the length of this algebra.
Length function is an…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3664:field_when:0:20
SUMMARY:How large is the character degree sum compared to the character table sum for a finite group?
DTSTART:2024-06-16T10:15:00
DTEND:2024-06-16T11:30:00
DSCRIPTION:Speaker: Arvind Ayyer (IISC, Bangalore)\n
Abstract:
Link to the recording
In 1961, Solomon proved that the sum of all the entries in the character
table of a finite group does not exceed the cardinality of the group.
We state a different and incomparable property here -- this sum is at
most twice the sum of degrees of the irreducible characters. Although
this is not true in general, it seems to hold for "most" groups. We
establish the validity of this property for symmetric, hyperoctahedral
and demihyperoctahedral groups. Using these…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3663:field_when:0:21
SUMMARY:On flag-no-square 4-manifolds
DTSTART:2024-06-09T11:00:00
DTEND:2024-06-09T12:30:00
DSCRIPTION:Speaker: Daniel Kalmanovich (Ariel Univ.)\n
Abstract:
Link to the recording
Which 4-manifolds admit a flag-no-square triangulation? Just one family of examples, described by Przytycki and Swiatkowski, was known.
We introduce two “gluing” operations which allow us to construct new examples of flag-no-square 4-manifolds.
Furthermore, our construction technique may be of independent interest: we take copies of a single such 4-manifold
(which we know very little about) and carefully apply our operations to obtain 4-manifolds…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3654:field_when:0:22
SUMMARY:Topological and mixing properties for algebraic groups over local fields in characteristic zero
DTSTART:2024-06-05T07:30:30
DTEND:2024-06-05T08:30:00
DSCRIPTION:Speaker: Elyasheev Leibtag (Weizmann Institute of Science)\n
Abstract:
We show that for algebraic groups over local fields of characteristic zero, the following are equivalent:
Every homomorphism has a closed image, every unitary representation decomposes into a direct sum of finite- dimensional and mixing representations, and the matrix coefficients are dense within the algebra of weakly almost periodic functions over the group.
In our proof, we employ methods from semi-group theory. We establish that these groups are compactification-…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3662:field_when:0:23
SUMMARY:Triangle-free triple systems
DTSTART:2024-06-02T11:00:00
DTEND:2024-06-02T12:30:00
DSCRIPTION:Speaker: Ron Holzman (Technion)\n
Abstract:
Link to the recording
There are four non-isomorphic configurations of triples that can form a triangle in a 3-uniform hypergraph. Forbidding different combinations of these four configurations,
fifteen extremal problems can be defined, several of which already appeared in the literature in some different context.
Here we systematically study all of these problems solving the new cases exactly or asymptotically.
In many cases we also characterize…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3653:field_when:0:24
SUMMARY:Intersection of a sequence of outer models, part 2
DTSTART:2024-05-30T11:00:00
DTEND:2024-05-30T13:00:00
DSCRIPTION:Speaker: Zhixing You (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3652:field_when:0:25
SUMMARY:First steps in non-commutative dynamics over the quaternions and the octonions
DTSTART:2024-05-29T07:30:00
DTEND:2024-05-29T08:30:00
DSCRIPTION:Speaker: Solomon Vishkautsan (Tel-Hai Academic College)\n
Abstract:
We present results on the dynamics of standard univariate polynomials over quaternions and octonions from an algebraic point of view. We look at periodic and fixed points and emphasize the need to carefully define what we mean by these terms when it comes to dynamics over non-commutative rings. For quadratic monics over the octonions, we provide criteria for classifying fixed points as attracting, repelling, or "ambivalent", generalizing the complex case. This is a joint…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3651:field_when:0:26
SUMMARY:Quadratic residue patterns, algebraic curves, and a K3 surface (to the memory of Lydia Goncharova)
DTSTART:2024-05-22T07:30:00
DTEND:2024-05-22T08:30:00
DSCRIPTION:Speaker: Mikhail Tsfasman (CNRS and Independent University of Moscow)\n
Abstract:
Quadratic residue (modulo a prime) patterns have been studied since the end of the 19th century. My talk consists of two formally independent parts, closely related in spirit.
The first part is devoted to the classical problem on strings of consecutive quadratic residues. We reduce this problem to counting points on elliptic and hyperelliptic curves, thus obtaining results unavailable by classical methods.
In the second part, I shall state the last unpublished result…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3661:field_when:0:27
SUMMARY:Stirling numbers, Koszul duality and cohomology of configuration spaces
DTSTART:2024-05-19T15:05:00
DTEND:2024-05-19T16:05:00
DSCRIPTION:Speaker: Sheila Sundaram (UMN)\n
Abstract:
Link to the recording
The unsigned Stirling numbers c(n,k) of the first kind give the Hilbert function for two algebras
associated to the hyperplane arrangement in type A, the Orlik-Solomon algebra and the graded Varchenko-Gelfand
algebra. Both algebras carry symmetric group actions with a rich structure, and
have been well studied by topologists, algebraists and combinatorialists: the first coincides with the Whitney homology
of the partition lattice, and the second with a well-…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3646:field_when:0:28
SUMMARY:Intersection of a sequence of outer models, part 1
DTSTART:2024-05-16T13:00:00
DTEND:2024-05-16T15:00:00
DSCRIPTION:Speaker: Zhixing You (BIU)\n
Abstract:
The technique of taking the intersection of a sequence of outer models is understudied in the field of Mathematical Logic. With Assaf Rinot and Jiachen Yuan, we find it to be quite effective for constructing some interesting sum ultrafilters. In this talk, I will first illustrate how we use it to answer questions about indecomposable ultrafilters and $\delta$-complete uniform ultrafilters, and then extend some results in infinitary combinatorics. A sample result is that we…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3648:field_when:0:29
SUMMARY:Spaces with vanishing characteristic coefficients
DTSTART:2024-05-15T07:30:00
DTEND:2024-05-15T08:30:00
DSCRIPTION:Speaker: Adam Chapman (Academic College of Tel-Aviv-Yaffo)\n
Abstract:
We study subspaces of central simple algebras where some of the characteristic coefficients vanish. The main result is that in the generic tensor product of n cyclic algebras of degree p over a field F, the maximal dimension of a space over which the first p-1 characteristic coefficients vanish is (p^{2n} - 1)/(p-1).
The result is obtained by a neat combinatorial observation communicated to the speaker by Terence Tao and Gjergji Zaimi via math overflow…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3660:field_when:0:30
SUMMARY:Local h-polynomials, uniform triangulations and real-rootedness
DTSTART:2024-05-12T15:00:00
DTEND:2024-05-12T16:00:00
DSCRIPTION:Speaker: Christos Athanasiadis (Univ. of Athens)\n
Abstract:
Link to the recording
The local h-polynomial is a fundamental enumerative invariant
of a triangulation Δ of a simplex. This talk aims to review its
remarkable combinatorial properties, discuss nice examples and address
the following question: Which triangulations of the simplex have a
real-rooted h-polynomial? Our main result states that this is the case
when Δ is the barycentric subdivision of any triangulation of the
simplex. The proof is based on a new combinatorial formula for…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3645:field_when:0:31
SUMMARY:Splitting families of sets, part 2
DTSTART:2024-05-09T13:00:00
DTEND:2024-05-09T15:00:00
DSCRIPTION:Speaker: Tal Kagalovsky (BGU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3647:field_when:0:32
SUMMARY:Elementary and non-elementary inclusive varieties
DTSTART:2024-05-08T07:30:00
DTEND:2024-05-08T08:30:00
DSCRIPTION:Speaker: Grigory Mashevitzky (Ben Gurion University of the Negev)\n
Abstract:
The class of identical inclusions was defined by E. S. Lyapin. This is a class of universal formulas which is situated strictly between identities and universal positive formulas. These universal formulas can be written as identical equalities of subsets of words: elements of the free semigroup. Classes of semigroups defined by identical inclusions are called inclusive varieties. The language of identical inclusions is much richer than the language of…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3659:field_when:0:33
SUMMARY:Square root crystals and Grothendieck positivity
DTSTART:2024-05-05T11:05:00
DTEND:2024-05-05T12:54:05
DSCRIPTION:Speaker: Eric Marberg (HKUST)\n
Abstract:
Link to the recording
The classical theory of type A crystals provides a graphical framework for proving Schur positivity results.
In this talk we will discuss a new category of "square root crystals" (introduced implicitly in the work of Yu) that can be used to establish instances of Grothendieck positivity.
For example, Buch's combinatorial interpretation of the coefficients expanding products of symmetric Grothendieck functions has a simple…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3644:field_when:0:34
SUMMARY:Splitting families of sets, part 1
DTSTART:2024-05-02T11:00:00
DTEND:2024-05-02T13:00:00
DSCRIPTION:Speaker: Tal Kagalovsky (BGU)\n
Abstract:
I will present several known results in the topic of splitting families of sets. Miller’s splitting theorem from 1937 was proven for finite n > 0 and ρ-uniform families where ρ is infinite. Under the assumptions of GCH and without the use of more modern tools, this approach is generalized here in order to prove several stronger theorems by Erdős and Hajnal.
Then a more modern approach by Kojman will be presented, where he used Shelah’s RGCH in order to eliminate the GCH from some…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3643:field_when:0:35
SUMMARY:A perfect space whose square is not cmc
DTSTART:2024-04-18T11:00:00
DTEND:2024-04-18T13:00:00
DSCRIPTION:Speaker: Shira Yadai (BIU)\n
Abstract:
We present a consistent construction of a topological space that is perfect (all closed sets are G_delta) whose square is not countably metacompact.
This is joint work with Assaf Rinot
END:VEVENT
BEGIN:VEVENT
UID:calendar:3637:field_when:0:36
SUMMARY:A special T(rho_1)
DTSTART:2024-04-11T11:00:00
DTEND:2024-04-11T13:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BGU)\n
Abstract:
We give a criterion on a C-sequence which implies that the associated tree T(rho_1) is special. In particular such a tree exists in ZFC. This answers Question 2.2.18 from Todorcevic' walks book. We prove some related results.
This is joint work with Assaf Rinot
END:VEVENT
BEGIN:VEVENT
UID:calendar:3636:field_when:0:37
SUMMARY:Geodesic taxicab paths in the Sierpinski carpet, Menger sponge, and their generalizations
DTSTART:2024-03-31T09:00:00
DTEND:2024-03-31T10:00:00
DSCRIPTION:Speaker: Ethan Berkove (Lafayette College)\n
Abstract:
The Sierpinski carpet and Menger sponge are well-studied connected generalizations of the Cantor set. They are also members of a two-parameter family of connected higher-dimensional fractals that can be constructed from the $n$-cube as iterated function systems.
In this talk we focus on taxicab paths—piece-wise linear paths that always travel parallel to a coordinate axis with possible limiting behavior at the endpoints—between any two points $x$ and $y$ in members of…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3634:field_when:0:38
SUMMARY:A topological Ramsey theorem
DTSTART:2024-03-28T12:00:00
DTEND:2024-03-28T14:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BGU)\n
Abstract:
We prove Galvin's conjecture: for every colouring of pairs of reals into finitely-many colours, there is a set homeomorphic to the rationals on which at most two colours are taken
END:VEVENT
BEGIN:VEVENT
UID:calendar:3631:field_when:0:39
SUMMARY:On indecomposable ultrafilters at every successor of singular, part 6
DTSTART:2024-03-21T12:00:00
DTEND:2024-03-21T14:00:00
DSCRIPTION:Speaker: Inbar Oren (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3628:field_when:0:40
SUMMARY:Residue structures
DTSTART:2024-03-13T08:30:00
DTEND:2024-03-13T09:30:00
DSCRIPTION:Speaker: Louis Rowen (Bar-Ilan University)\n
Abstract:
We consider residue structures $R/G$ where $(G,+)$ is an additive subgroup of a ring $(R,+,\cdot)$, not necessarily an ideal. Special instances include Krasner's construction of quotient hyperfields, and Dickson's construction of nonassociative algebras. The residue construction, treated formally, satisfies the Noether isomorphism theorems, and may be cast in a setting which includes direct products and tensor products.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3630:field_when:0:41
SUMMARY:From elliptic curves to Ceresa cycles
DTSTART:2024-03-10T10:00:00
DTEND:2024-03-10T11:00:00
DSCRIPTION:Speaker: Ari Shnidman (Hebrew University)\n
Abstract:
Given an algebraic variety X, and two subvarieties Y, Y', can Y be deformed to Y' within X?
More generally, we would like to understand the different "deformation classes" of subvarieties of X of a given dimension. For topological deformations, the answer is given by singular cohomology and is rather well understood. For algebraic deformations, the answer is quite mysterious and depends heavily on the ground field. In codimension 1, this amounts to studying rational…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3624:field_when:0:42
SUMMARY:On indecomposable ultrafilters at every successor of singular, part 5
DTSTART:2024-03-07T12:00:00
DTEND:2024-03-07T14:00:00
DSCRIPTION:Speaker: Inbar Oren (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3629:field_when:0:43
SUMMARY:Special elements in the lattice of semigroup varieties
DTSTART:2024-03-06T08:30:00
DTEND:2024-03-06T09:30:00
DSCRIPTION:Speaker: Dmitry Skokov (Ural Federal University)\n
Abstract:
Special elements in the lattice of semigroup varieties
END:VEVENT
BEGIN:VEVENT
UID:calendar:3623:field_when:0:44
SUMMARY:From algebraic geometry and combinatorics to physics
DTSTART:2024-03-03T10:00:00
DTEND:2024-03-03T11:00:00
DSCRIPTION:Speaker: Yelena Mandelshtam (Berkeley)\n
Abstract:
In the search for mathematical explanations for physical phenomena, algebraic geometry and combinatorics have made surprising appearances.
In this talk, I will overview some exciting results connecting combinatorics and algebraic geometry to water waves (coming from the Kadomtsev-Petviashvili equation) and to particle physics (coming from scattering amplitudes).
END:VEVENT
BEGIN:VEVENT
UID:calendar:3622:field_when:0:45
SUMMARY:On indecomposable ultrafilters at every successor of singular, part 4
DTSTART:2024-02-29T12:00:00
DTEND:2024-02-29T14:00:00
DSCRIPTION:Speaker: Inbar Oren (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3620:field_when:0:46
SUMMARY:On geometric versions of Zarankiewicz’s problem
DTSTART:2024-02-25T10:00:00
DTEND:2024-02-25T11:00:00
DSCRIPTION:Speaker: Shakhar Smorodinsky (Ben-Gurion University)\n
Abstract:
Extremal combinatorics poses a fundamental question: How large can a system be while avoiding certain configurations? A classic instance of this inquiry arises in extremal graph theory: Given a fixed graph H, what is the maximum number ex(n, H) of edges a graph G on n vertices can have if it excludes H as a subgraph? This problem remains widely open for H being a complete bipartite graph and is known as Zarankiewicz’s problem.
Even when considering algebraic…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3621:field_when:0:47
SUMMARY:On indecomposable ultrafilters at every successor of singular, part 3
DTSTART:2024-02-22T12:00:00
DTEND:2024-02-22T14:00:00
DSCRIPTION:Speaker: Inbar Oren (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3615:field_when:0:48
SUMMARY:Morphisms of theta lifts of non-trivial automorphic characters of the orthogonal group
DTSTART:2024-02-21T08:30:00
DTEND:2024-02-21T09:30:00
DSCRIPTION:Speaker: Ron Erez (Tel Aviv University)\n
Abstract:
This work is inspired by Kobi Snitz's 2003 Ph.D. thesis, where he constructed two irreducible, automorphic, cuspidal representations of the metaplectic group (a double cover of SL_2(A), where A are the adeles) from global theta lifts of orthogonal groups and non-trivial automorphic quadratic characters. Snitz constructed isomorphisms between these representations for certain matching data of quadratic spaces and automorphic quadratic characters which can be thought of as an…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3613:field_when:0:49
SUMMARY:What is ... a measurable entire function?
DTSTART:2024-02-18T10:00:00
DTEND:2024-02-18T11:00:00
DSCRIPTION:Speaker: Mikhail Sodin (Tel-Aviv University)\n
Abstract:
In the talk, I plan to discuss the notion of measurable entire functions, introduced by Benjy Weiss around 25 years ago, as well as several related results and questions.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3619:field_when:0:50
SUMMARY:On indecomposable ultrafilters at every successor of singular, part 2
DTSTART:2024-02-15T12:00:00
DTEND:2024-02-15T14:00:00
DSCRIPTION:Speaker: Inbar Oren (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3614:field_when:0:51
SUMMARY:Rank-stability of polynomial equations
DTSTART:2024-02-14T08:30:00
DTEND:2024-02-14T09:30:00
DSCRIPTION:Speaker: Tomer Bauer (Bar-Ilan University)\n
Abstract:
Ulam's stability problem asks when an 'almost' solution of an equation is 'close' to an exact solution. Extending the thoroughly studied theory of group stability, we study Ulam stability type problems for associative and Lie algebras. Namely, we investigate obstacles to rank-approximation of 'almost' solutions by exact solutions for systems of non-commutative polynomial equations.
This leads to a rich theory of stable associative and Lie algebras, with connections to linear…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3609:field_when:0:52
SUMMARY:Random graphs, statistical physics and complexity
DTSTART:2024-02-11T10:00:00
DTEND:2024-02-11T11:00:00
DSCRIPTION:Speaker: Amir Dembo (Stanford)\n
Abstract:
Statistical physics models for disordered materials provide precise predictions about the typical complexity of certain combinatorial optimization problems. The underlying common structure is that of many discrete variables, whose interaction is represented by a random sparse graph.
I will discuss recent progress in proving some of these predictions. In particular, on the emerging theory of nonlinear large deviations, yielding mean field approximation for certain…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3606:field_when:0:53
SUMMARY:On indecomposable ultrafilters at every successor of singular, part 1
DTSTART:2024-02-08T12:00:00
DTEND:2024-02-08T14:00:00
DSCRIPTION:Speaker: Inbar Oren (HUJI)\n
Abstract:
Indecomposability of an ultrafilter is a weakening of a completeness of an ultrafilter. Ben-David and Magidor showed that it is possible to obtain an indecomposable ultrafilter at א_{ω+1}. In our work, we extend their result to obtain indecomposable ultrafilters at every successor of a singular cardinal. This result will be the focus of our talks.
We will also provide applications in two separate directions. Firstly, we will apply one of Shelah’s results to obtain a model where the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3616:field_when:0:54
SUMMARY:The connection between quadratic forms and Hassett-maximal cubic fourfolds
DTSTART:2024-02-07T08:30:00
DTEND:2024-02-07T09:30:00
DSCRIPTION:Speaker: Elad Gal (Technion)\n
Abstract:
Let S be a set of natural numbers. Is it possible to find an integral n-ary quadratic form with f(Z^n)=S?
In this lecture we will discuss integral quadratic forms and questions of representability of natural numbers by quadratic forms. We will define "formally-supported sets" and present some types of questions that should be asked about such sets and forms. Mainly, we will be concerned with one specific example of a formally-supported subset, and using its properties to compute the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3610:field_when:0:55
SUMMARY:Integrators of matrices
DTSTART:2024-02-04T10:00:00
DTEND:2024-02-04T11:00:00
DSCRIPTION:Speaker: Suren Danielian (Bar-Ilan University)\n
Abstract:
The notion of matrix integration was introduced in 2007 by Bhat and Mukherjee [1], as a natural counterpart to the classical notion of matrix differentiation [2]. It has several motivations in various areas, including the geometry of polynomials -- an extensive topic with many beautiful open problems, for example, Sendov's conjecture.
Not every matrix has an integral, and the problem of existence of integrable and non-integrable matrices with a given Jordan structure has…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3605:field_when:0:56
SUMMARY:Forcing with models as side conditions, part 7
DTSTART:2024-02-01T12:00:00
DTEND:2024-02-01T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3617:field_when:0:57
SUMMARY:Distinction of the Steinberg representation with respect to a symmetric pair
DTSTART:2024-01-31T08:30:00
DTEND:2024-01-31T09:30:00
DSCRIPTION:Speaker: Jiandi Zou (Technion)\n
Abstract:
Let G be a reductive group over a non-archimedean local field F of odd residual characteristic, let theta be an involution of G over F, and let H be the connected component of the theta-fixed subgroup of G. We are interested in the problem of distinction of the Steinberg representation St of G restricted to H. More precisely, first we give a reasonable upper bound of the dimension of the complex…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3603:field_when:0:58
SUMMARY:Linear algebraic and combinatorial problems in matrix majorization
DTSTART:2024-01-28T10:00:00
DTEND:2024-01-28T11:00:00
DSCRIPTION:Speaker: Pavel Shteyner (Bar-Ilan University)\n
Abstract:
The origins of majorization theory can be found in a variety of different contexts. The most notable examples are Muirhead's work on symmetric polynomials, Schur's work on Hadamard's inequality, and works by Lorenz and Dalton on income distributions. Hardy, Littlewood, and Polya laid the foundations of majorization as an independent theory.
Vector majorization is a preorder notion on the real vector space. A vector x is majorized by a vector y if, for any k, the sum of the k…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3604:field_when:0:59
SUMMARY:Forcing with models as side conditions, part 6
DTSTART:2024-01-25T12:00:00
DTEND:2024-01-25T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3618:field_when:0:60
SUMMARY:Width of words in linear groups
DTSTART:2024-01-24T08:30:00
DTEND:2024-01-24T09:30:00
DSCRIPTION:Speaker: Pavel Gvozdevsky (Bar-Ilan University)\n
Abstract:
A word is an element in a free group. Given a word w and a group G, we have the word map defined by substitution. The set of values w(G) consists of the image of this map and the inverses of elements of the image. The width of the word w in the group G is the minimal constant C such that every element of <w(G)> can be expressed as the product of C elements of w(G).
The…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3602:field_when:0:61
SUMMARY:Forcing with models as side conditions, part 5
DTSTART:2024-01-18T12:00:00
DTEND:2024-01-18T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3597:field_when:0:62
SUMMARY:Smooth invariants and isolated quotient singularities
DTSTART:2024-01-17T08:30:30
DTEND:2024-01-17T09:30:00
DSCRIPTION:Speaker: Amiram Braun (Haifa University)\n
Abstract:
Let G<GL(V) be a finite group, and let V be a finite-dimensional vector space over a field F. Then G acts as a group of automorphisms on S(V) ,the symmetric algebra of V.
We shall consider the following question: When is S(V)^G, the subring of G- invariants, a polynomial ring? This had been completely settled by Shephard-Todd- Chevalley-Serre, if (char F,|G|)=1,and is still open otherwise.
We shall describe our recent solution to this problem for G…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3600:field_when:0:63
SUMMARY:Left barrier loss for unbiased survival analysis prediction
DTSTART:2024-01-14T10:00:00
DTEND:2024-01-14T11:00:00
DSCRIPTION:Speaker: Yoram Louzoun (Bar-Ilan University)\n
Abstract:
Survival analysis (SA) prediction involves the prediction of the time until an event of interest occurs (TTE), based on input attributes. The main challenge of SA is instances where the event is not observed (censored), typically through an alternative (censoring) event. Most SA prediction methods suffer from drawbacks limiting the usage of advanced machine learning methods: Ignoring the input of the censored samples, no separation between model and loss, typical small datasets and…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3601:field_when:0:64
SUMMARY:Forcing with models as side conditions, part 4
DTSTART:2024-01-11T12:00:00
DTEND:2024-01-11T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3598:field_when:0:65
SUMMARY:Semiassociative algebras over a field
DTSTART:2024-01-10T08:30:00
DTEND:2024-01-10T09:30:00
DSCRIPTION:Speaker: Guy Blachar (Bar-Ilan University)\n
Abstract:
Associative central simple algebras are a classical subject, related to many areas of study including Galois cohomology and algebraic geometry. An associative central simple algebra is a form of matrices because a maximal étale subalgebra acts on the algebra faithfully by left and right multiplication. In an attempt to extract and isolate the full potential of this point of view, we study nonassociative algebras whose nucleus contains an étale subalgebra bi-acting faithfully on the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3599:field_when:0:66
SUMMARY:Geometric inequalities for convex sets and valuations theory
DTSTART:2024-01-07T10:00:00
DTEND:2024-01-07T11:00:00
DSCRIPTION:Speaker: Semyon Alesker (Tel-Aviv University)\n
Abstract:
Valuations are finitely additive measures on convex sets. The space of translation-invariant valuations carries a number of structures ( i.e., product and convolution), satisfying non-trivial properties. One such recently discovered property is an analogue of the classical Hodge-Riemann relations from algebraic geometry. In special cases, they lead to new inequalities on convex bodies, to be discussed in the talk.
No preliminary knowledge of valuation theory or algebraic…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3596:field_when:0:67
SUMMARY:Omega-bounded ladder systems
DTSTART:2024-01-04T12:00:00
DTEND:2024-01-04T13:45:00
DSCRIPTION:Speaker: Assaf Rinot\n
Abstract:
Leiderman and Szeptycki proved that a single Cohen real introduces a ladder system L over w1 for which the corresponding space X_L is not a Delta-space. They asked whether there is a ZFC example of a ladder system L over some cardinal kappa for which X_L is not countably metacompact, in particular, not a Delta-space. In a paper from August, we gave an affirmative answer with kappa=cf(beth_{w+1}), but we got the feedback that the biggest interest is ladder systems consisting of ladders…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3594:field_when:0:68
SUMMARY:Schmidt rank/strength and the singular locus
DTSTART:2024-01-03T08:30:00
DTEND:2024-01-03T09:30:00
DSCRIPTION:Speaker: Amichai Lampert (University of Michigan)\n
Abstract:
The Schmidt rank/strength of a polynomial is an algebraic measure of its non-degeneracy. It has proven very useful for studying questions regarding polynomials of fixed degree in arbitrarily many variables: Schmidt used it to count integer solutions for systems of polynomial equations with rational coefficients, Green and Tao used it to investigate the distribution of values of polynomials over finite fields, and Ananyan and Hochster used it to prove Stillman's conjecture on…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3591:field_when:0:69
SUMMARY:Forcing with models as side conditions, part 3
DTSTART:2023-12-28T12:00:00
DTEND:2023-12-28T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3595:field_when:0:70
SUMMARY:Acyclic complexes and finitistic dimensions
DTSTART:2023-12-27T08:30:00
DTEND:2023-12-27T09:30:00
DSCRIPTION:Speaker: Liran Shaul (Charles University, Prague)\n
Abstract:
Over any ring, any bounded above acyclic cochain complex of projectives is null-homotopic. Similarly, any bounded below acyclic cochain complex of injectives is null-homotopic. In this talk we consider dual problems, and relate them to the finitistic dimension conjecture, and many other major open problems in homological algebra.
================================================
https://us02web.zoom.us/j/87856132062
Meeting ID: 878 5613 2062
END:VEVENT
BEGIN:VEVENT
UID:calendar:3590:field_when:0:71
SUMMARY:The vanishing levels of a tree
DTSTART:2023-12-26T12:00:00
DTEND:2023-12-26T14:00:00
DSCRIPTION:Speaker: Zhixing You (BIU)\n
Abstract:
We prove the consistency of the existence of a kappa-Souslin tree whose set of vanishing levels is a club in a model where all nontrivial C-sequences over kappa are trivial. This is joint work with Assaf Rinot and Jiachen Yuan.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3593:field_when:0:72
SUMMARY:Diamond on Kurepa trees, part 2
DTSTART:2023-12-26T09:00:00
DTEND:2023-12-26T11:00:00
DSCRIPTION:Speaker: Ziemek Kostana (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3592:field_when:0:73
SUMMARY:Poncelet's closure theorem and three levels of its understanding
DTSTART:2023-12-24T08:00:00
DTEND:2023-12-24T09:30:00
DSCRIPTION:Speaker: George Shabat (Russian State University for the Humanities and Independent University of Moscow)\n
Abstract:
Poncelet's 1814 theorem
states that whenever a triangle is inscribed in one circle and circumscribed another one, the triangle belongs to the continuous
family of triangles that are all inscribed in and circumscribe the same two circles.
This theorem will be presented as
(1) an "obvious" fact of elementary geometry;
(2) as a rather difficult high-school theorem;
(3) as a quite natural result of adult mathematics.
The level (3) needs some understanding of complex…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3588:field_when:0:74
SUMMARY:Forcing with models as side conditions, part 2
DTSTART:2023-12-21T12:00:00
DTEND:2023-12-21T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3589:field_when:0:75
SUMMARY:Diamond on Kurepa trees
DTSTART:2023-12-19T12:00:00
DTEND:2023-12-19T14:00:00
DSCRIPTION:Speaker: Ziemek Kostana (BIU)\n
Abstract:
We shall prove independence results concerning diamond on Kurepa trees. This is joint work with Assaf Rinot and Saharon Shelah.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3587:field_when:0:76
SUMMARY:Models of elliptic curves, using model theory
DTSTART:2023-12-17T10:00:00
DTEND:2023-12-17T11:00:00
DSCRIPTION:Speaker: Yatir Halevi (Haifa University)\n
Abstract:
Given a valued field (K,v) with valuation ring O and an algebraic group G over K, a model of G is a group scheme \mathcal{G} over O for which \mathcal{G}\times_O K=G. We exhibit the existence of such models for G an elliptic curve and K an algebraically closed field and on the way we classify the different group schemes one can get. The proof uses a combination of tools from model theory and algebraic geometry.
The aim of this talk is to state the theorem and to…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3586:field_when:0:77
SUMMARY:Forcing with models as side conditions, part 1
DTSTART:2023-12-12T12:00:00
DTEND:2023-12-12T14:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
A decade ago, Neeman introduced a new method of forcing using two-type of models as side conditions. In 2015, Kuziljevic and Todor\'cevi\'c generalized Todor\'cevi\'c's $\epsilon$-chain of elementary sub-models to a matrices of countable elementary sub-models which are used to force a $\diamond^+$ sequence and fast clubs on $\omega_1$. A year ago, Curial Gallart Rodr\'iguez was able to combine this two methods and thus introducing a two-type symmetric matrices.
We will go…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3582:field_when:0:78
SUMMARY:Identifying underlying geometry to denoise and analyze (high-dimensional) data
DTSTART:2023-12-03T13:00:00
DTEND:2023-12-03T14:00:00
DSCRIPTION:Speaker: Shira Faigenbaum-Golovin (Duke University)\n
Abstract:
In many applications that involve large volumes of data (whether low- or high-dimensional), identifying and exploiting the underlying geometry is an essential ingredient; this is also the case in many of the research projects on which I have worked. In my talk, I will concentrate mainly on two projects.
In the first project, optimization techniques are used to determine an optimal low-dimensional smooth manifold (without imposing its dimension a priori) approximating a…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3576:field_when:0:79
SUMMARY:מבוא למייפל
DTSTART:2023-11-30T16:00:00
DTEND:2023-11-30T18:00:00
DSCRIPTION:Speaker: פרופ' ג'רמי שיף\n
Abstract:
הרצאה שלישית
ההרצאה תעסוק בדוגמאות נוספות: מסלולים מחזוריים ומידות אינווריאנטיות במערכות דינמיות, פתרון לוחות סודוקו, משחק נחשים וסולמות.
מייפל ומתמטיקה הן שתי חבילות התוכנה המסחריות הגדולות לביצוע מתמטיקה. המיני-קורס הזה נועד לסטודנטים (במתמטיקה, מדעי המחשב, הנדסה, פיזיקה, כימיה ועוד) להכיר את השימוש הבסיסי במייפל, כך שלאחר מכן הם יוכלו לנצל את התוכנה במהלך התואר, לעזור בפתרון בעיות, וככלי לחקור ולהעמיק את ההבנה בכל תחומי המתמטיקה.
רוב הקורס יהיה נגיש לכל סטודנט שסיים את…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3583:field_when:0:80
SUMMARY:Minimal non-sigma-scattered linear order, part 2
DTSTART:2023-11-30T10:00:02
DTEND:2023-11-30T10:04:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
Continuing the lecture from June, we show how to furthermore get a large antichain of minimal non-sigma-scattered linear orders
END:VEVENT
BEGIN:VEVENT
UID:calendar:3581:field_when:0:81
SUMMARY:Learning dynamics of nonconvex models in high dimension
DTSTART:2023-11-26T10:00:00
DTEND:2023-11-26T11:00:00
DSCRIPTION:Speaker: Inbar Seroussi (Tel-Aviv University)\n
Abstract:
Stochastic gradient descent (SGD) stands as a cornerstone of optimization and modern machine learning. However, a complete understanding of why SGD performs so well remains a major challenge.
In this talk, I will present a mathematical theory for SGD in high dimensions when both the number of samples and problem dimensions are large. We show that the dynamics of SGD, applied to generalized linear models and multi-index problems, with data possessing a general…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3575:field_when:0:82
SUMMARY:מבוא למייפל
DTSTART:2023-11-23T16:00:00
DTEND:2023-11-23T18:00:00
DSCRIPTION:Speaker: פרופ' ג'רמי שיף\n
Abstract:
הרצאה שניה
ההרצאה תעסוק ביסודות התכנות: לולאות ותנאים. דוגמאות: פתרון משוואות והתפצלויות, ספירת מספרים ראשוניים ותכונותיהם.
מייפל ומתמטיקה הן שתי חבילות התוכנה המסחריות הגדולות לביצוע מתמטיקה. המיני-קורס הזה נועד לסטודנטים (במתמטיקה, מדעי המחשב, הנדסה, פיזיקה, כימיה ועוד) להכיר את השימוש הבסיסי במייפל, כך שלאחר מכן הם יוכלו לנצל את התוכנה במהלך התואר, לעזור בפתרון בעיות, וככלי לחקור ולהעמיק את ההבנה בכל תחומי המתמטיקה.
רוב הקורס יהיה נגיש לכל סטודנט שסיים את בחינת הבגרות…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3578:field_when:0:83
SUMMARY:On a quantitative version of Harish-Chandra's regularity theorem and singularities of representations
DTSTART:2023-11-22T08:30:00
DTEND:2023-11-22T09:30:00
DSCRIPTION:Speaker: Yotam Hendel (KU Leuven)\n
Abstract:
Let G be the F points of a connected reductive group defined over a local field F of characteristic 0. By Harish-Chandra’s regularity theorem, every character Θ(π) of an irreducible representation π of G is given by a locally integrable function f_π on G. It turns out that f_π has even better integrability properties, namely, it is locally L^{1+r}-integrable for some r>0. This gives rise to a new singularity invariant of representations \e_π.
We explore \e_π, and determine…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3573:field_when:0:84
SUMMARY:מספרים אלגבריים ונעלים
DTSTART:2023-11-20T12:30:00
DTEND:2023-11-20T13:30:00
DSCRIPTION:Speaker: פרופ' מיכאל שיין\n
Abstract:
מספר ממשי, או מרוכב, נקרא אלגברי אם הוא שורש של פולינום עם מקדמים שלמים. לדוגמא, השורש של 2 ויחס הזהב אלגבריים כי הם שורשים של x^2 - 2 ושל x^2 - x - 1, בהתאמה. מספר שאינו אלגברי נקרא טרנסצנדנטי, או, בעברית, נעלה. למרות שמספר ממשי אקראי יהיה נעלה בהסתברות של 100%, זה לא קל למצוא דוגמאות ספציפיות של מספרים נעלים. בשיעור הזה נדבר על החשיבות של מספרים אלגבריים ונעלים ונוכיח כי e נעלה. נשתמש רק בתכונות הבסיסיות של אינטגרלים מאינפי 2.
…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3577:field_when:0:85
SUMMARY:Inverse theorems in ergodic theory and additive combinatorics
DTSTART:2023-11-19T15:00:00
DTEND:2023-11-19T16:00:00
DSCRIPTION:Speaker: Or Shalom (IAS, Princeton)\n
Abstract:
The Gowers uniformity k-norm on a finite abelian group measures the averages of complex functions on such groups over k-dimensional arithmetic cubes. The inverse question about these norms asks if a large norm implies correlation with a function of an algebraic origin.
The analogue of the Gowers uniformity norms for measure-preserving abelian actions are the Host-Kra-Gowers seminorms, which are intimately connected to the Host-Kra-Ziegler factors of such systems. The…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3574:field_when:0:86
SUMMARY:מבוא למייפל
DTSTART:2023-11-16T16:00:00
DTEND:2023-11-16T18:00:00
DSCRIPTION:Speaker: פרופ' ג'רמי שיף\n
Abstract:
הרצאה ראשונה
פונקציונליות בסיסית של מייפל, משתנים ופונקציות, גרפיקה בסיסית וחקירת פונקציות, כמה פקודות מחבילת LinearAlgebra.
מייפל ומתמטיקה הן שתי חבילות התוכנה המסחריות הגדולות לביצוע מתמטיקה. המיני-קורס הזה נועד לסטודנטים (במתמטיקה, מדעי המחשב, הנדסה, פיזיקה, כימיה ועוד) להכיר את השימוש הבסיסי במייפל, כך שלאחר מכן הם יוכלו לנצל את התוכנה במהלך התואר, לעזור בפתרון בעיות, וככלי לחקור ולהעמיק את ההבנה בכל תחומי המתמטיקה.
רוב הקורס יהיה נגיש לכל סטודנט שסיים את בחינת הבגרות…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3571:field_when:0:87
SUMMARY:Lattice methods for modular forms
DTSTART:2023-11-12T15:00:00
DTEND:2023-11-12T16:00:00
DSCRIPTION:Speaker: Eran Assaf (Dartmouth College)\n
Abstract:
Following Kneser, we survey the notion of neighboring lattices and how the study of the neighboring relation on lattices gives rise to modular forms, with a focus on applications to the Arthur-Langlands conjectures, concerning automorphic forms for orthogonal and symplectic groups.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3570:field_when:0:88
SUMMARY:Combinatorial wall-crossing via the Mullineux involution
DTSTART:2023-11-12T10:00:00
DTEND:2023-11-12T11:00:00
DSCRIPTION:Speaker: Galyna Dobrovolska (Ariel University)\n
Abstract:
The rational Cherednik algebra H_c is an algebra of interest in modern representation theory, which is a degeneration of the double affine Hecke algebra, introduced by Cherednik to prove Macdonald's conjectures about properties of Macdonald polynomials. For values of c lying in chambers separated by walls, representations of H_c are labeled by partitions. Combinatorial wall-crossing is a bijection from the set of irreducible representations of H_c to the set of irreducible…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3569:field_when:0:89
SUMMARY:על תורים , התנהגות אסימפטוטית, ואסטרטגיות חניה במגרש חד מימדי.
DTSTART:2023-11-09T17:00:00
DTEND:2023-11-09T18:30:00
DSCRIPTION:Speaker: פרופ' גידי עמיר\n
Abstract:
תור (כמו בסופר, לא בקומיקס) הוא מערכת הנשלטת על ידי שני תהליכים בזמן– תהליך "הגעה" ותהליך "שירות". כאשר מגיע אדם הוא נעמד בסוף התור וכאשר יש שירות האדם הראשון בתור עוזב. תורים משמשים מרכיב חשוב בבעיות רבות במתמטיקה, פיזיקה ובאלגוריתמים. בהרצאה נלמד קצת על תורים ועל ההתנהגות האסימפטוטית שלהם, ונראה איך הם קשורים לאסטרטגיות חניה במגרש חד מימדי. ההרצאה תכלול גם עבודה משותפת מהזמן האחרון עם איתי ארמה,כמו גם מספר שאלות פתוחות שיכולות להוות פרויקטי מחקר לעבודה לתואר שני.
קהל: …
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BEGIN:VEVENT
UID:calendar:3568:field_when:0:90
SUMMARY:מעברי פאזה בתורת ההסתברות
DTSTART:2023-11-07T12:30:00
DTEND:2023-11-07T14:00:00
DSCRIPTION:Speaker: נועם ברגר\n
Abstract:
מעברי פאזה הם תופעה נפוצה מאוד בעולם הפיזיקאלי. בהרצאה זו ננסה להבין קצת מהמתמטיקה שעומדת מאחורי התופעה. לצורך כך נציג כמה מודלים, חלקם פיזיקליים וחלקם לא, וננתח את התנהגותם, בדגש על מעברי הפאזה.
קהל: מי שלקח את הקורסים מבוא להסתברות ואינפי
END:VEVENT
BEGIN:VEVENT
UID:calendar:3565:field_when:0:91
SUMMARY:יעודכן בהמשך
DTSTART:2023-11-02T12:00:00
DTEND:2023-11-02T13:00:00
DSCRIPTION:Speaker: פרופ’ נתן קלר\n
Abstract:
יעודכן בהמשך
END:VEVENT
BEGIN:VEVENT
UID:calendar:3564:field_when:0:92
SUMMARY: גיאומטריה ספקטראלית — לשמוע את צורת התוף
DTSTART:2023-11-01T12:00:00
DTEND:2023-11-01T13:00:00
DSCRIPTION:Speaker: ד"ר שמעון ברוקס\n
Abstract:
צליל שמשמיע מיתר של גיטרה תלוי באורך המיתר; וצלילים של כלי נשיפה תלויים באורכם של צינורות. הקשר הזה מתואר על ידי פתרון משוואה דיפרנציאלית פשוטה, אבל ההכללה שלה למימד 2 ומעלה מובילה למד״ח מורכבת יותר, שתכונותיה קשורות לגיאומטריה של התחום בצורה שעדיין מסתורית מאוד. בהרצאה נסייר מעט בהתפתחות התחום הזה, מהניסויים באקוסטיקה של כלדני ב1800, דרך גיאומטריה דיפרנציאלית, מערכות דינמיות והתורה הקוונטית, תורת המספרים, ותורת הגרפים, עד לשאלות פתוחות בוערות בימינו.
**אין…
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BEGIN:VEVENT
UID:calendar:3563:field_when:0:93
SUMMARY:שלושה משפטי צביעה מפורסמים
DTSTART:2023-10-30T12:00:18
DTEND:2023-10-30T13:00:00
DSCRIPTION:Speaker: פרופ’ בועז צבאן\n
Abstract:
נציג הוכחות אלמנטריות לכמה משפטים מפורסמים לגבי צביעות של אובייקטים מתמטיים.בין השאר נפגוש את המשפט המתמטי החשוב ביותר שהגה פילוסוף וכלכלן, את הסמל של גוגל, מפות מדיניות אינסופיות, ונראה איך זה קשור למשפט האחרון של פרמה.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3562:field_when:0:94
SUMMARY:הרצאה על המרחב הוקטורי של הצליל
DTSTART:2023-10-29T15:00:00
DTEND:2023-10-29T16:00:00
DSCRIPTION:Speaker: ד"ר ארז שיינר\n
Abstract:
ההרצאה מיועדת למסיימי שנה א
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BEGIN:VEVENT
UID:calendar:3566:field_when:0:95
SUMMARY:תהליכי מרקוב
DTSTART:2023-10-26T12:00:00
DTEND:2023-10-26T13:00:00
DSCRIPTION:Speaker: פרופ' עוזי וישנה\n
Abstract:
תהליכי מרקוב
END:VEVENT
BEGIN:VEVENT
UID:calendar:3561:field_when:0:96
SUMMARY:תואר ראשון במתמטיקה והמסלול האקדמי
DTSTART:2023-10-26T11:00:00
DTEND:2023-10-26T12:32:26
DSCRIPTION:Speaker: ד”ר אייל סובג\n
Abstract:
ד"ר אייל סובג, יועץ אקדמי לתואר ראשון, שנה א' יסביר על התואר הראשון במתמטיקה ועל המשך הדרך האקדמית. יתאר במבט מאקרו את קורסי הליבה בתואר הראשון במתמטיקה. ויחלוק מניסיונו כולל טיפים שימושיים. ינתן זמן לשאלות ותשובות.
ההרצאה מיועדת לסטודנטים חדשים במתמטיקה אך פתוחה לכולם.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3560:field_when:0:97
SUMMARY:ריבוע הריבוע
DTSTART:2023-10-25T14:00:00
DTEND:2023-10-25T15:00:00
DSCRIPTION:Speaker: גיא בלשר\n
Abstract:
בתחילת המאה ה-20 עלתה השאלה הבאה: האם ניתן לרצף ריבוע על ידי (מספר סופי של) ריבועים קטנים יותר, כך שבריצוף לא נשתמש בשני ריבועים בעלי אותו אורך צלע? בהרצאה נדון בסיפור ההיסטורי של הבעיה ובפתרון שלה. כחידה לקראת ההרצאה, מוזמנים לחשוב על השאלה הבאה: האם ניתן לרצף קוביה על ידי (מספר סופי של) קוביות קטנות יותר, כך שבריצוף לא נשתמש בשתי קוביות בעלות אותו אורך מקצוע?
ההרצאה לא תדרוש רקע מוקדם (כדאי לדעת מה זה ריבוע).
END:VEVENT
BEGIN:VEVENT
UID:calendar:3559:field_when:0:98
SUMMARY:הילוכים אקראיים על חבורות
DTSTART:2023-10-25T11:00:00
DTEND:2023-10-25T12:00:00
DSCRIPTION:Speaker: פרופ' גידי עמיר\n
Abstract:
נגדיר ונדבר על הילוכים אקראיים על גרפים ועל חבורות נוצרות סופית, ונסקור קשרים בין תכונות של ההילוכים האקראיים הללו לתכונות גיאומטריות ואלגבריות של החבורה. אין צורך בידע מוקדם מעבר למושג החבורה, הגרף, ומבוא להסתברות.
ההרצאה מיועדתלשנה ג וסטודנטים לתואר שני, או כל מי שיודע מה זו חבורה.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3558:field_when:0:99
SUMMARY:על משחקים עם מזל
DTSTART:2023-10-23T14:00:00
DTEND:2023-10-23T15:00:00
DSCRIPTION:Speaker: ד"ר ארז שיינר\n
Abstract:
ההרצאה מיועדת למסיימי שנה ב, מתאים לכל הרמות .
END:VEVENT
BEGIN:VEVENT
UID:calendar:3551:field_when:0:100
SUMMARY:Demushkin groups of uncountable rank
DTSTART:2023-09-20T07:00:00
DTEND:2023-09-20T08:30:00
DSCRIPTION:Speaker: Tamar Bar-On (Oxford)\n
Abstract:
Demushkin groups play an important rule in number theory, being the maximal pro-p Galois groups of local fields. In 1996 Labute presented a generalization of the theory for countably infinite rank pro-p groups, and proved that the p-Sylow subgroups of the absolute Galois groups of local fields are Demushkin groups of infinite countable rank. These results were extended by Minac & Ware, who gave necessary and sufficient conditions for Demushkin groups of infinite countable rank to…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3549:field_when:0:101
SUMMARY:Universality problem for wide Aronszajn trees, part 3
DTSTART:2023-09-12T09:00:00
DTEND:2023-09-12T11:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3538:field_when:0:102
SUMMARY:Universality problem for wide Aronszajn trees, part 2
DTSTART:2023-09-05T09:00:00
DTEND:2023-09-05T11:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3537:field_when:0:103
SUMMARY:Universality problem for wide Aronszajn trees, part 1
DTSTART:2023-08-31T11:00:00
DTEND:2023-08-31T13:00:00
DSCRIPTION:Speaker: Omer Ben-Neria (HUJI)\n
Abstract:
The university problem for a class K of structures asks if there is a structure M in K such that every other structure in K embeds into. I will start by relating the universality problem for the class of wide Aronszajn trees to generalized descriptive set theory, and specifically to generalizations of Scott's theorem on the complexity of isomorphism classes in generalized Baire spaces. Next, we will see that in L there is a strong failure of this universality problem.…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3533:field_when:0:104
SUMMARY:Products of positive definite quadratic forms
DTSTART:2023-08-10T07:30:00
DTEND:2023-08-10T08:30:00
DSCRIPTION:Speaker: Marco Zaninelli (Universiteit Antwerpen)\n
Abstract:
In 1927, E. Artin solved Hilbert’s 17th problem and showed that real positive definite forms are exactly the quotients of sums of squares of forms, but did not provide any bound on the number of squares appearing in such sums. In 1967, A. Pfister showed for every natural number n that all positive definite forms in R(X_1, …, X_n) are sums of 2^n squares. When restricting to quadratic forms, this bound is easily seen not to be optimal. In this talk, based on joint…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3534:field_when:0:105
SUMMARY:On generlized Ehrenfeucht-Mostowski models
DTSTART:2023-08-03T11:00:00
DTEND:2023-08-03T13:00:00
DSCRIPTION:Speaker: Ido Feldman (BIU)\n
Abstract:
One of the main question in generalized descriptive set theory is whether there is generalized Borel-reducibility counterpart of Shelah's main gap theorem.
Which is stated as follows:
Let $T_1$ be a classifiable theory and $T_2$ a non-classifiable theory. Is there a Borel reduction from the isomorphism relation of $T_1$ to the isomorphism relation of $T_2$?
This question was studied by Friedman, Hyttinen, and Weinstein (former Kulikov), who gave a positive answer to this question for…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3531:field_when:0:106
SUMMARY:Restrictions of Ultrapower Embeddings from Generic Extensions to their Ground Model
DTSTART:2023-07-20T11:00:00
DTEND:2023-07-20T13:00:00
DSCRIPTION:Speaker: Eyal Kaplan (TAU)\n
Abstract:
Assume that V[G] is a generic (set) forcing over the ground model V, and let \kappa be a measurable cardinal in V[G].
Let j_W \colon V[G] \to M be an ultrapower embedding associated with a normal measure W\in V[G] on \kappa.
What can be said about j_W\restriction_{V}? Is it definable in V? Is it an iterated ultrapower of V by its measures/extenders?
We will survey some known results. These results do not apply to the case where the forcing being used is an…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3530:field_when:0:107
SUMMARY:Reflecting topological spaces through elementary submodels, part 3
DTSTART:2023-07-13T11:00:00
DTEND:2023-07-13T13:00:00
DSCRIPTION:Speaker: Rodrigo Rey Carvalho (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3527:field_when:0:108
SUMMARY:Reflecting topological spaces through elementary submodels, part 2
DTSTART:2023-07-06T11:00:00
DTEND:2023-07-06T13:00:00
DSCRIPTION:Speaker: Rodrigo Rey Carvalho (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3511:field_when:0:109
SUMMARY:Reflecting topological spaces through elementary submodels, part 1
DTSTART:2023-06-22T11:00:00
DTEND:2023-06-22T13:00:00
DSCRIPTION:Speaker: Rodrigo Rey Carvalho (BIU)\n
Abstract:
In this series of talks I will present the notion of $X_M$, that is, a topological space $X$ as seen through an elementary submodel $M$. This concept first appeared in the paper ``The topology of elementary submodels", by L. Junqueira and F. Tall. One of the central topics of this field is to question whether topological properties can be preserved through this operation, both ``upwards" and ``downwards". I will focus on covering properties, giving a panorama of where we stand…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3503:field_when:0:110
SUMMARY:Minimal non-sigma-scattered linear order of size an inaccessible, part 1
DTSTART:2023-06-15T11:00:00
DTEND:2023-06-16T13:00:00
DSCRIPTION:Speaker: Roy Shalev (BIU)\n
Abstract:
In a recent paper, Cummings, Eisworth and Moore gave the first consistent example of a minimal non-sigma-scattered linear order of size greater than Aleph_1. Their construction works for arbitrary successor cardinals, and leaves open the case of inaccessibles. In this talk, we will give a construction that covers this missing case.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3494:field_when:0:111
SUMMARY:Bracket width of Lie algebras of vector fields on affine curves
DTSTART:2023-06-14T07:30:00
DTEND:2023-06-14T08:30:00
DSCRIPTION:Speaker: Ievgen Makedonskyi (Beijing Institute of Mathematical Sciences and Applications)\n
Abstract:
We study Lie algebras of vector fields on smooth affine curves with a trivial tangent bundle. These Lie algebras consist of multiples of one derivation and are simple. It was proven by A. Dubouloz, B. Kunyavskii and A. Regeta that the bracket width of such an algebra is strictly greater than one if the curve is not rational and has a unique place at infinity. We prove that the bracket widths of Lie algebras of vector fields on smooth affine curves with a trivial…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3502:field_when:0:112
SUMMARY:Projection onto a Capped Rotated Second-Order Cone with Applications to Sparse Regression Relaxations
DTSTART:2023-06-11T07:00:00
DTEND:2023-06-11T08:00:00
DSCRIPTION:Speaker: Ishy Zagdoun (Bar Ilan)\n
Abstract:
This paper establishes a closed-form expression for projecting onto a capped rotated second-order cone. This special object is a convex set that arises as a part of the feasible region of the perspective relaxation of mixed-integer nonlinear programs (MINLP) with binary indicator variables. The rapid computation of the projection onto this convex set enables the development of effective methods for solving the continuous relaxation of MINLPs whose feasible region may…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3500:field_when:0:113
SUMMARY:The life-cycle of random walkers on random regular graph
DTSTART:2023-06-08T10:00:00
DTEND:2023-06-08T11:00:00
DSCRIPTION:Speaker: Eytan Katzav (Huji)\n
Abstract:
Random walks (RWs) on networks have been extensively studied due to their relevance in various fields including Mathematics, Physics and Computer Science. RWs serve as a versatile tool for understanding the underlying network as well as dynamical processes that take place on them. Focusing on Random Regular Graphs (RRGs), I will present various analytical results describing important events in the life-cycle of RWs on RRGs, namely the distributions of the first hitting time, the first…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3498:field_when:0:114
SUMMARY:Weakly reflecting graph properties
DTSTART:2023-06-08T09:00:02
DTEND:2023-06-08T09:04:00
DSCRIPTION:Speaker: Attila Joó (Hamburg)\n
Abstract:
We'll discuss our recent preprint.
END:VEVENT
BEGIN:VEVENT
UID:calendar:3497:field_when:0:115
SUMMARY:Labeling irreducible modules for Hecke algebras of type A
DTSTART:2023-06-07T07:30:00
DTEND:2023-06-07T08:30:00
DSCRIPTION:Speaker: Ola Amara-Omari and Malka Schaps (Bar-Ilan University)\n
Abstract:
The irreducible modules in the blocks of a tower of Hecke algebras of rank e are labeled by certain multipartitions called e-regular. The best-known case is for blocks of the symmetric groups over a field of characteristic p, where the rank e is p, and the multipartitions are just partitions. In general, the e-regular multipartions are generated recursively.
We consider a crystal in which the vertices are blocks, generated by Chevalley generators f_i. If we…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3496:field_when:0:116
SUMMARY:Infinite game theory, part 3
DTSTART:2023-06-01T11:30:00
DTEND:2023-06-01T13:00:00
DSCRIPTION:Speaker: Ron Peretz (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3495:field_when:0:117
SUMMARY:Twist conjugacy zeta functions and Reidemeister spectrum
DTSTART:2023-05-31T07:30:00
DTEND:2023-05-31T08:30:00
DSCRIPTION:Speaker: Paula Macedo Lins de Araujo (University of Lincoln)\n
Abstract:
A group automorphism f: G —> G induces the action g \cdot x=gx f(g)^{-1} on G. The orbits of such action are called twisted conjugacy classes (also known as Reidemeister classes). The number of such classes for a fixed automorphism is called its Reidemeister number.
One reason for the interest in Reidemeister numbers is that they might give information on the number of fixed points of continuous self-maps of manifolds. One of the main goals in the area is…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3480:field_when:0:118
SUMMARY:Galois cohomology of reductive groups over number fields
DTSTART:2023-05-24T07:30:00
DTEND:2023-05-24T08:30:00
DSCRIPTION:Speaker: Mikhail Borovoi (Tel Aviv University)\n
Abstract:
Let G be a connected reductive group over a global field F (a number field or a global function field). Let M=\pi_1(G) denote the *algebraic fundamental group* of G, which is a certain finitely generated abelian group endowed with an action of the absolute Galois group Gal(F^s/F). Using and generalizing a result of Tate for tori, we give a closed formula for the Galois cohomology set H^1(F,G) in terms of the Galois module M and the Galois cohomology sets H^1(F_v,G) for the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3487:field_when:0:119
SUMMARY:Infinite game theory, part 2
DTSTART:2023-05-18T11:00:00
DTEND:2023-05-18T13:00:00
DSCRIPTION:Speaker: Ron Peretz (BIU)\n
Abstract:
We continue
END:VEVENT
BEGIN:VEVENT
UID:calendar:3481:field_when:0:120
SUMMARY:Electrical networks and Lagrangian Grassmannians
DTSTART:2023-05-17T07:30:00
DTEND:2023-05-17T08:30:00
DSCRIPTION:Speaker: Boris Bychkov (Haifa University)\n
Abstract:
An electrical network is a graph in a disk with positive
weights on edges. The set of response matrices of a (compactified) set
of electrical networks admits an embedding into the totally
nonnegative Grassmannian $\mathrm{Gr}_{\geq 0}(n-1,2n)$. I will talk
about a new parameterization of the space of electrical networks which
defines an embedding into the Grassmannian $\mathrm{Gr}(n-1,V)$, where
$V$ is a certain subspace of dimension $2n-2$ and moreover an
embedding into the totally…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3482:field_when:0:121
SUMMARY:Automorphisms of the category of free non-associative algebras with unit
DTSTART:2023-05-10T07:30:00
DTEND:2023-05-10T08:30:00
DSCRIPTION:Speaker: Elena Aladova (Universidade de São Paulo)\n
Abstract:
Let $\Theta$ be an arbitrary variety of algebras and $\Theta^0$ the category of all free finitely generated algebras in $\Theta$ .
The group $Aut(\Theta^0)$ of automorphisms of the category $\Theta^0$ plays an important role in universal algebraic geometry. It turns out that for a wide class of varieties, the group $Aut(\Theta^0)$ can be decomposed into a product of the subgroup $Inn(\Theta^0)$ of inner automorphisms and the subgroup $St(\Theta^0)$ of strongly stable…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3483:field_when:0:122
SUMMARY:Infinite game theory, part 1
DTSTART:2023-05-04T11:00:00
DTEND:2023-05-05T13:00:00
DSCRIPTION:Speaker: Ron Peretz (BIU)\n
Abstract:
An invitation to the subject
END:VEVENT
BEGIN:VEVENT
UID:calendar:3479:field_when:0:123
SUMMARY:Highly versal torsors
DTSTART:2023-05-03T07:00:00
DTEND:2023-05-03T08:30:00
DSCRIPTION:Speaker: Uriya First (Haifa University)\n
Abstract:
Let G be a linear algebraic group over a field k. Recall that a G-torsor E-->X, where X is a k-variety, is said to be weakly versal if every G-torsor over a k-field is a specialization of E-->X. It is called versal, resp. strongly versal, when such specializations are abundant in a well-defined sense. Versal torsors are important to the study of essential dimension and also to cohomological invariants.
I will present some recent results about the…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3477:field_when:0:124
SUMMARY:Saturation properties of ideals, part 2
DTSTART:2023-04-27T11:00:00
DTEND:2023-04-27T13:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BGU)\n
Abstract:
TBA
END:VEVENT
BEGIN:VEVENT
UID:calendar:3474:field_when:0:125
SUMMARY:Saturation properties of ideals, part 1
DTSTART:2023-04-20T11:00:00
DTEND:2023-04-20T13:00:00
DSCRIPTION:Speaker: Tanmay Inamdar (BGU)\n
Abstract:
TBA
END:VEVENT
BEGIN:VEVENT
UID:calendar:3478:field_when:0:126
SUMMARY:On the localization method in Chevalley groups
DTSTART:2023-04-19T07:30:00
DTEND:2023-04-19T08:30:00
DSCRIPTION:Speaker: Helen Bunina (Bar-Ilan University)\n
Abstract:
Every commutative ring R with 1 is naturally embedded into the direct product of the localizations of R at its maximal ideals. This construction is very useful for different problems in Chevalley groups over rings. We will talk about two applications: description of automorphisms and isomorphisms of Chevalley groups over arbitrary rings and double centralizers of elementary unipotent elements in these groups. We will also mention the Diophantine problem in Chevalley groups, its proof…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3472:field_when:0:127
SUMMARY:Controlling the existence of isomorphisms between Souslin trees
DTSTART:2023-03-30T11:00:00
DTEND:2023-03-30T13:00:00
DSCRIPTION:Speaker: Shira Greenstein-Yadai (BIU)\n
Abstract:
TBA
END:VEVENT
BEGIN:VEVENT
UID:calendar:3467:field_when:0:128
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:0:129
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3466:field_when:0:130
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3464:field_when:0:131
SUMMARY:Club isomorphisms on higher Aronszajn trees
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:0:132
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:0:133
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:0:134
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:0:135
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:0:136
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:0:137
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:0:138
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3507:field_when:0:139
SUMMARY:יום ולילה בקופנהגן- הזמנים ההלכתיים בקהילה הצפונית
DTSTART:2023-01-10T15:45:00
DTEND:2023-01-10T17:00:00
DSCRIPTION:Speaker: מר פינחס מלכיאור \n
Abstract:
השנה מציינים בדנמרק 400 שנה להשתקעותם של יהודים ראשונים בממלכה. הם הגיעו בעקבות הזמנת המלך כריסטיאן ה-IV ליהודים פורטוגזיים לסייע לו בהקמת עיר חדשה, שתתחרה בעיר המבורג על ההגמוניה המסחרית בצפון אירופה. המיזם לא הצליח, אך בזכותו נפתחה הממלכה בפני יהודים, וב-1684 נוסדה הקהילה היהודית בקופנהגן, ובעקבותיה נוסדו קהילות גם במספר ערים נוספות. מספר היהודים היה תמיד קטן, אלפים בודדים בבירה ומאות אחדות בערי השדה.
ב-1833 נחנך בית-הכנסת המפואר של קופנהגן, המשמש את הקהילה עד היום הזה. תחילה הופיע…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3450:field_when:0:140
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”…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3451:field_when:0:141
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:0:142
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:0:143
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3444:field_when:0:144
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:0:145
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3443:field_when:0:146
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:0:147
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:0:148
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3437:field_when:0:149
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:0:150
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:0:151
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3440:field_when:0:152
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:0:153
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3435:field_when:0:154
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3433:field_when:0:155
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:0:156
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:0:157
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:0:158
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:0:159
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:0:160
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3428:field_when:0:161
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:0:162
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:0:163
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3419:field_when:0:164
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:0:165
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}/…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3422:field_when:0:166
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:0:167
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:0:168
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:0:169
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:0:170
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:0:171
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:0:172
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:0:173
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:0:174
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:0:175
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3400:field_when:0:176
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:0:177
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:0:178
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3396:field_when:0:179
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:0:180
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:0:181
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:0:182
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:0:183
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:0:184
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:0:185
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:0:186
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,…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3369:field_when:0:187
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:0:188
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:0:189
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3364:field_when:0:190
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:0:191
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3359:field_when:0:192
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3358:field_when:0:193
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:0:194
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,…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3354:field_when:0:195
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3357:field_when:0:196
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3356:field_when:0:197
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:0:198
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:0:199
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:0:200
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:0:201
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:0:202
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3347:field_when:0:203
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:0:204
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3346:field_when:0:205
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3344:field_when:0:206
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:0:207
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:0:208
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:0:209
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:0:210
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3330:field_when:0:211
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3332:field_when:0:212
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:0:213
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:0:214
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.…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3328:field_when:0:215
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3329:field_when:0:216
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3325:field_when:0:217
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:0:218
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:0:219
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:0:220
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3317:field_when:0:221
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3318:field_when:0:222
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3316:field_when:0:223
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:0:224
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3315:field_when:0:225
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3312:field_when:0:226
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:0:227
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:0:228
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:0:229
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3307:field_when:0:230
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:0:231
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:0:232
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:0:233
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:0:234
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:0:235
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3295:field_when:0:236
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:0:237
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:0:238
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:0:239
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 (…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3288:field_when:0:240
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:0:241
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3284:field_when:0:242
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:0:243
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:0:244
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:0:245
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:0:246
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:0:247
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:0:248
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:0:249
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:0:250
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…
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BEGIN:VEVENT
UID:calendar:3277:field_when:0:251
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…
END:VEVENT
BEGIN:VEVENT
UID:calendar:3274:field_when:0:252
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.
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BEGIN:VEVENT
UID:calendar:3273:field_when:0:253
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:0:254
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:0:255
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:0:256
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…
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BEGIN:VEVENT
UID:calendar:3271:field_when:0:257
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 …
END:VEVENT
BEGIN:VEVENT
UID:calendar:3253:field_when:0:258
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…
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BEGIN:VEVENT
UID:calendar:3267:field_when:0:259
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:0:260
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…
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END:VCALENDAR