tag:www.math.bgu.ac.il,2005:/en/research/seminars/agnt/meetingsBGU AGNTProf. Amnon Besserbessera@bgu.ac.ilhttps://www.math.bgu.ac.il/~bessera/2018-10-12T09:43:08+03:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/4492018-10-12T09:43:08+03:002018-10-12T09:43:12+03:00<span class="mathjax">Avner Segal: “Poles of the Standard L-function and Functorial Lifts for G2” expanded, part I</span>October 17, 15:10—16:25, 2018, -101<div class="mathjax"><p>This is part 1 of the speaker’s talk from last semester, expanded into a two-part series.</p>
<p>The functoriality conjecture is a key ingredient in the theory of automorphic forms and the Langlands program. Given two reductive groups G and H, the principle of functoriality asserts that a map r:G^->H^ between their dual complex groups should naturally give rise to a map r*:Rep(G)->Rep(H) between their automorphic representations. In this talk, I will describe the idea of functoriality, its connection to L-functions and recent work on weak functorial lifts to the exceptional group of type G_2.</p></div>Avner Segalhttps://scholar.google.ca/citations?user=fSSRIIAAAAAJ&hl=enBar Ilantag:www.math.bgu.ac.il,2005:MeetingDecorator/4502018-10-12T09:45:31+03:002018-10-13T19:41:15+03:00<span class="mathjax">Zev Rosengarten: Tamagawa Numbers of Linear Algebraic Groups over Function Fields</span>October 24, 15:10—16:25, 2018, -101<div class="mathjax"><p>In 1981, Sansuc obtained a formula for Tamagawa numbers of reductive groups over number fields, modulo some then unknown results on the arithmetic of simply connected groups which have since been proven, particularly Weil’s conjecture on Tamagawa numbers over number fields. One easily deduces that this same formula holds for all linear algebraic groups over number fields. Sansuc’s method still works to treat reductive groups in the function field setting, thanks to the recent resolution of Weil’s conjecture in the function field setting by Lurie and Gaitsgory. However, due to the imperfection of function fields, the reductive case is very far from the general one; indeed, Sansuc’s formula does not hold for all linear algebraic groups over function fields. We give a modification of Sansuc’s formula that recaptures it in the number field case and also gives a correct answer for pseudo-reductive groups over function fields. The commutative case (which is essential even for the general pseudo-reductive case) is a corollary of a vast generalization of the Poitou-Tate nine-term exact sequence, from finite group schemes to arbitrary affine commutative group schemes of finite type. Unfortunately, there appears to be no simple formula in general for Tamagawa numbers of linear algebraic groups over function fields beyond the commutative and pseudo-reductive cases. Time permitting, we may discuss some examples of non-commutative unipotent groups over function fields whose Tamagawa numbers (and relatedly, Tate-Shafarevich sets) exhibit various types of pathological behavior.</p></div>Zev RosengartenHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/4512018-10-12T09:58:02+03:002018-10-13T19:39:43+03:00<span class="mathjax">Avner Segal: Poles of the Standard L-function and Functorial Lifts for G2</span>October 31, 15:10—16:25, 2018, -101<div class="mathjax"><p>This is part 2 of 2 of an expanded version of the speaker’s talk from last semester.</p>
<p>The functoriality conjecture is a key ingredient in the theory of automorphic forms and the Langlands program. Given two reductive groups G and H, the principle of functoriality asserts that a map r:G^->H^ between their dual complex groups should naturally give rise to a map r*:Rep(G)->Rep(H) between their automorphic representations. In this talk, I will describe the idea of functoriality, its connection to L-functions and recent work on weak functorial lifts to the exceptional group of type G_2.</p></div>Avner Segalhttps://scholar.google.ca/citations?user=fSSRIIAAAAAJ&hl=enBar Ilantag:www.math.bgu.ac.il,2005:MeetingDecorator/4642018-11-05T13:26:36+02:002018-11-05T13:26:49+02:00<span class="mathjax">Kieran Ryan: Some Schur-Weyl Dualities</span>November 7, 15:10—16:25, 2018, -101<div class="mathjax"><p>Schur-Weyl Duality is a remarkable theorem giving an intimate link between the representation theories of the Symmetric group S_n, and the General Linear group GL(k). Such a link also holds between other objects, in particular the Brauer Algebra and the Orthogonal group, and the Walled Brauer algebra and GL(k). I will give an introduction to these relationships.</p></div>Kieran RyanQueen Mary University of Londontag:www.math.bgu.ac.il,2005:MeetingDecorator/4662018-11-08T16:06:44+02:002018-11-08T17:22:05+02:00<span class="mathjax">Stephen Moore: The Representation Theory of the finite and infinite Temperley-Lieb algebras</span>November 14, 15:10—16:25, 2018, -101<div class="mathjax"><p>The Temperley-Lieb algebras are a family of finite dimensional algebras that are quotients of the symmetric groups algebras, or more generally the Iwahori-Hecke algebras. They appear in a number of areas of mathematics, including statistical mechanics, knot theory, quantum groups, and subfactors. We review their representation theory and give some results on an infinite dimensional generalization.</p></div>Stephen MooreBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/4592018-10-25T12:19:04+03:002018-11-22T12:27:40+02:00<span class="mathjax">Avner Segal: Structure of Degenerate Principal Series of Exceptional Groups</span>November 28, 15:10—16:25, 2018, -101<div class="mathjax"><p>The reducibility and structure of parabolic inductions is a basic problem in the representation theory of p-adic groups. Of particular interest is its principal series and degenerate principal series representations, that is parabolic induction of 1-dimensional representations of Levi subgroups. In this talk, I will start by describing the functor of normalized induction and its left adjoint the Jacquet functor and by going through several examples in the group SL_4(Q_p) will describe an algorithm which can be used to determine reducibility of such representations. This algorithm is the core of a joint project with Hezi Halawi, in which we study the structure of degenerate principal series of exceptional groups of type En (see https://arxiv.org/abs/1811.02974).</p></div>Avner Segalhttp://www.segalavner.comBar Ilantag:www.math.bgu.ac.il,2005:MeetingDecorator/4482018-10-11T12:48:36+03:002018-12-02T15:51:25+02:00<span class="mathjax">Nadya Gurevich : The Zoo of Integral Representations for L-functions</span>December 5, 15:10—16:25, 2018, -101<div class="mathjax"><p>Automorphic L-functions, initially defined on some right half plane, are conjectured to be have
meromorphic continuation to the whole complex plane. An effective method to prove this in some cases is by using an integral representation. Since the 1960’s, many such integrals were discovered, some of them representing the same L-function, but seemingly unrelated. Using recent discoveries of D.Ginzburg and D. Soudry, I will explain the relation between different integrals representing the same L-function.</p></div>Nadya Gurevich https://www.math.bgu.ac.il/~ngur/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/4522018-10-13T19:36:47+03:002018-12-09T15:29:47+02:00<span class="mathjax">Ilya Tyomkin: Tropicalizations, tropical reductions and liftings of curves with differentials</span>December 12, 15:10—16:25, 2018, -101<div class="mathjax"><p>Tropicalizations and tropical reductions provide a convenient tool to control degenerations of algebraic objects. Roughly speaking, a tropicalization is a piecewise linear object, associated to an algebraic object over a non-Archimedean field, that contains essential information about one of its integral models. The tropical reduction is then the reduction of the model over the residue field. For applications, it is often important not only to describe the tropicalization process, but also to be able to decide whether something that looks like the tropicalization and the tropical reduction comes from an algebraic object. Such statements are called lifting theorems.
Tropical techniques have been applied successfully to a number of problems in algebraic geometry, such as enumerative questions, dimension estimates, descriptions of compactifications etc. In particular, in a recent work of Bainbridge, Chen, Gendron, Grushevsky, and Moeller, a tropical approach was used to describe a new compactification of the space of smooth curves with differentials (although the authors don’t use this terminology). The proofs of BCGGM rely on transcendental techniques.
In my talk, I will present a modified version of BCGGM tropicalization, and will indicate an algebraic proof of the main result. The talk is based on a joint work with M.Temkin.</p></div>Ilya Tyomkinhttps://ilyatyomkin.wixsite.com/mathBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/4372018-10-09T10:21:34+03:002018-12-13T09:49:28+02:00<span class="mathjax">Kevin Coulembier: Tensor categories in positive characteristic</span>December 19, 15:10—16:25, 2018, -101<div class="mathjax"><p>Tensor categories are abelian k-linear monoidal categories modeled on the representation categories of affine (super)group schemes over k. Deligne gave very succinct intrinsic criteria for a tensor category to be equivalent to such a representation category, over fields k of characteristic zero. These descriptions are known to fail badly in prime characteristics. In this talk, I will present analogues in prime characteristic of these intrinsic criteria. Time permitting, I will comment on the link with a recent conjecture of V. Ostrik which aims to extend Deligne’s work in a different direction.</p></div>Kevin Coulembierhttp://www.maths.usyd.edu.au/u/kevinc/University of Sydneytag:www.math.bgu.ac.il,2005:MeetingDecorator/4382018-10-09T10:25:48+03:002018-12-25T16:42:06+02:00<span class="mathjax">Vera Serganova : Support varieties for supergroups</span>December 26, 15:10—16:25, 2018, -101<div class="mathjax"><p>We define a functor from the category of representations of algebraic supergroups with reductive even part to the category of equivariant sheaves and show several applications of this construction to representation theory.</p></div>Vera Serganova https://math.berkeley.edu/people/faculty/vera-serganovaUC Berkeleytag:www.math.bgu.ac.il,2005:MeetingDecorator/4552018-10-16T10:35:08+03:002019-01-01T12:08:40+02:00<span class="mathjax">Tomer Schlank: Ambidexterity in the T(n)-Local Stable Homotopy Theory</span>January 2, 15:10—16:25, 2019, -101<div class="mathjax"><p>The monochromatic layers of the chromatic
filtration on spectra, that is the K(n)-local (stable 00-)categories Sp_{K(n)} enjoy many remarkable properties. One example is the vanishing of the Tate construction due to Hovey-Greenlees-Sadofsky. The vanishing of the Tate construction can be considered as a natural equivalence between the colimits and limits in Sp_{K(n)} parametrized by finite groupoids. Hopkins and Lurie proved a generalization of this result where finite groupoids are replaced by arbitrary \pi-finite 00-groupoids.</p>
<p>There is another possible sequence of (stable 00-)categories who can be considered as “monochromatic layers”, those are the T(n)-local 00-categories Sp_{T(n)}. For the Sp_{T(n)} the vanishing of the Tate construction was proved by Kuhn. We shall prove that the analog of Hopkins and Lurie’s result in for Sp_{T(n)}. Our proof will also give an alternative proof for the K(n)-local case.</p>
<p>This is a joint work with Shachar Carmeli and Lior Yanovski</p></div>Tomer Schlankhttps://mathematics.huji.ac.il/people/tomer-schlankHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/4722018-11-27T08:48:59+02:002019-05-02T17:03:13+03:00<span class="mathjax">Saurabh Singh: Reconstruction of formal schemes using their derived categories</span>January 9, 15:10—16:25, 2019, -101Saurabh SinghBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5282019-04-30T09:52:04+03:002019-04-30T09:52:04+03:00<span class="mathjax">Magnus Carlson: Chern-Simons theory for number fields.</span>May 1, 15:10—16:25, 2019, -101<div class="mathjax"><p>In a series of recent papers, Minhyong Kim defined an arithmetic analogue of topological Chern-Simons theory. In this talk, I will introduce this arithmetic Chern-Simons theory and then explain how to compute the arithmetic Chern-Simons invariant for finite, cyclic gauge groups. I will then give some recent applications of these computations.</p>
<p>My work in this talk is based on joint works with Tomer Schlank and Eric Ahlquist.</p></div>Magnus CarlsonHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/5322019-04-30T10:22:09+03:002019-05-01T18:20:21+03:00<span class="mathjax">Mattia Ornaghi : TBA</span>May 6, 15:10—16:25, 2019, -101Mattia Ornaghi tag:www.math.bgu.ac.il,2005:MeetingDecorator/5292019-04-30T09:53:26+03:002019-04-30T09:53:26+03:00<span class="mathjax">No Meeting: TBA</span>May 8, 15:10—16:25, 2019, -101No Meetingtag:www.math.bgu.ac.il,2005:MeetingDecorator/5302019-04-30T09:55:09+03:002019-05-13T22:23:08+03:00<span class="mathjax">Yakov Varshavsky: Perverse sheaves on certain infinite-dimensional spaces, and affine Springer theory</span>May 15, 15:10—16:25, 2019, -101<div class="mathjax"><p>A classical Springer theory is an important ingredient in the classification
of representations of finite groups of Lie type, completed by Lusztig.</p>
<p>The first result of this theory is the assertion that the so-called Grothendieck-Springer sheaf
is perverse and is equipped with an action of the Weyl group. Our main result asserts that an
analogous result also holds in the affine (infinite-dimensional) case.</p>
<p>In the first of my talk I will recall what are perverse sheaves, and why the Grothendieck-Springer
sheaf is perverse. In the rest of the talk I will outline how to extend all this to the affine setting.</p>
<p>We believe that this should have applications to the representations theory of p-adic groups.</p>
<p>This is a joint work with Alexis Bouthier and David Kazhdan</p></div>Yakov Varshavskyhttps://mathematics.huji.ac.il/people/yakov-varshavskyHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/5312019-04-30T10:18:34+03:002019-05-15T11:17:43+03:00<span class="mathjax">Sergey Fomin: Morsifications and mutations</span>May 22, 15:10—16:25, 2019, -101<div class="mathjax"><p>I will discuss a somewhat mysterious connection between singularity theory and cluster algebras, more specifically between the topology of isolated singularities of plane curves and the mutation equivalence of quivers associated with their morsifications. The talk will assume no prior knowledge of any of these topics. This is joint work with Pavlo Pylyavskyy, Eugenii Shustin, and Dylan Thurston.</p></div>Sergey Fominhttp://www.math.lsa.umich.edu/~fomin/University of Michigantag:www.math.bgu.ac.il,2005:MeetingDecorator/5362019-05-01T18:21:54+03:002019-05-01T18:21:54+03:00<span class="mathjax">Liran Shaul: TBA</span>May 29, 15:10—16:25, 2019, -101Liran Shaulhttps://liranshaul.wordpress.com/Charles University, Praguetag:www.math.bgu.ac.il,2005:MeetingDecorator/5332019-04-30T10:24:21+03:002019-05-07T20:22:48+03:00<span class="mathjax">Dan Edidin: A GIT characterization of cofree representations</span>June 5, 15:10—16:25, 2019, -101<div class="mathjax"><p>Let $V$ be a representation of a connected reductive group $G$. A representation is cofree if $k[V]$ is a free $k[V]^G$ module. There is a long history of work studying and classifying cofree representations of reductive groups. In this talk I present a simple conjectural characterization of cofree representations in terms of geometric invariant theory. Matt Satriano and I have proved the conjecture for irreducible representations of SL_n as well as for torus actions. I will give motiviation for the conjecture and explain the techniques which can be used for its verification. This talk based on joint work with Matt Satriano.</p></div>Dan Edidinhttps://faculty.missouri.edu/~edidind/University of Missouri, Columbiatag:www.math.bgu.ac.il,2005:MeetingDecorator/5342019-04-30T10:24:41+03:002019-06-11T15:18:46+03:00<span class="mathjax">Mattia Ornaghi : Localizations of the category of A_{\infty}-categories and Internal Homs (Part II).</span>June 12, 15:10—16:25, 2019, -101<div class="mathjax"><p>In this second talk we prove that the localizations of the categories of dg categories, of cohomologically unital and strictly unital A_\inftycategories with respect to the corresponding classes of quasi-equivalences are all equivalent. As an application, we give a complete proof of a claim by Kontsevich stating that the category of internal Homs for two dg categories can be described as the category of strictly unital A_\inftyfunctors between them. This is a joint work with Prof. A. Canonaco and Prof. P. Stellari arXiv:1811.07830.</p></div>Mattia Ornaghi HUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/5352019-04-30T10:26:43+03:002019-06-16T16:24:10+03:00<span class="mathjax">Lior Bary-Soroker: Number Theory in Function Fields.</span>June 19, 15:10—16:25, 2019, -101<div class="mathjax"><p>I will describe recent threads in the study of number theory in function fields, the different techniques that are used, the challenges, and if time permits the applications of the theory to other subjects such as probabilistic Galois theory.</p></div>Lior Bary-Sorokerhttp://www.math.tau.ac.il/~barylior/TAUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5692019-10-19T17:04:31+03:002019-10-23T11:21:23+03:00<span class="mathjax">David Jarossay: Computation of p-adic multiple zeta values and motivic Galois theory</span>October 30, 15:10—16:25, 2019, -101<div class="mathjax"><p>Multiple zeta values can be written as sums of series and as integrals. Their integral expression makes them into periods of the pro-unipotent fundamental groupoid of $\mathbb{P}^{1} - {0,1,\infty}$. p-Adic multiple zeta values are defined as p-adic analogues of these integrals. We will show how to express them as sums of series, which allows in particular to compute them explicitly.
We will mention the role of finite multiple zeta values defined by Kaneko and Zagier, and of a question asked by Deligne and Goncharov on a relation between the computation of p-adic multiple zeta values and their algebraic properties. To express the results we will introduce new objects in relation with motivic Galois theory of periods.</p></div>David JarossayBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5822019-10-23T16:04:49+03:002019-11-01T23:53:11+02:00<span class="mathjax">Alexei Entin: Factorization statistics for restricted polynomial specializations over large finite fields</span>November 6, 15:10—16:25, 2019, -101<div class="mathjax"><p>For a polynomial <span class="kdmath">$F(t,A_1,...,A_n)$</span> in <span class="kdmath">$\mathbb{F}_p[t,A_1,...,A_n]$</span> (<span class="kdmath">$p$</span> being a prime number) we study the factorization statistics of its specializations <span class="kdmath">$F(t,a_1,...,a_n)$</span> in <span class="kdmath">$\mathbb{F}_p[t]$</span> with <span class="kdmath">$(a_1,...,a_n) \in S$</span>, where <span class="kdmath">$S=I_1\times\dots\times I_n\subset\mathbb{F}_{p^n}$</span> is a box, in the limit <span class="kdmath">$p\rightarrow\infty$</span> and <span class="kdmath">$deg(F)$</span> fixed. We show that under certain fairly general assumptions on <span class="kdmath">$F$</span>, and assuming that the box dimensions grow to infinity with one of them growing faster than <span class="kdmath">$p^{1/2}$</span>, the degrees of the irreducible factors of <span class="kdmath">$F(t,a_1, \dots,a_n)$</span> are distributed like the cycle lengths of a random permutation in <span class="kdmath">$S_n$</span>.</p>
<p>This improves and generalizes previous results of Shparlinski and more recent results of Kurlberg-Rosenzweig, which in turn generalize the classical Polya-Vinogradov estimate of the number of quadratic residues in an interval.</p></div>Alexei Entinhttps://en-exact-sciences.tau.ac.il/profile/aentinTAUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5672019-10-06T12:24:43+03:002019-10-26T16:49:46+03:00<span class="mathjax">Sara Tukachinsky: Enumerating pseudoholomorphic curves with boundary</span>November 13, 15:10—16:25, 2019, -101<div class="mathjax"><p>Open Gromov-Witten (OGW) invariants should count pseudoholomorphic maps from curves with boundary to a symplectic manifold, with Lagrangian boundary conditions and various constraints on boundary and interior marked points. The presence of boundary of real codimension 1 poses an obstacle to invariance. In a joint work with J. Solomon (2016-2017), we defined genus zero OGW invariants under cohomological conditions. The construction is rather abstract. Nonetheless, in a recent work, also joint with J. Solomon, we find that the generating function of OGW has many properties that enable explicit calculations. Most notably, it satisfies a system of PDE called open WDVV (Witten-Dijkgraaf-Verlinde-Verlinde) equation. For the projective space, this PDE generates recursion relations that allow the computation of all invariants. Furthermore, the open WDVV can be reinterpreted as an associativity of a suitable version of a quantum product.</p>
<p>No prior knowledge of any of the above notions will be assumed.</p></div>Sara Tukachinskyhttp://www.math.ias.edu/~sarabt/IAStag:www.math.bgu.ac.il,2005:MeetingDecorator/5702019-10-20T10:53:29+03:002019-11-18T17:04:44+02:00<span class="mathjax">Haldun Özgür Bayindir : DGAs with polynomial homology</span>November 20, 15:10—16:25, 2019, -101<div class="mathjax"><p>Differential graded algebras(DGAs) are one of the most important
objects of study in homological algebra. These are chain complexes
with an associative and unital multiplication. Examples of DGAs
include cochain complexes of topological spaces equipped with the cup
product.</p>
<p>In this talk, I present our recent classification results on DGAs with
polynomial homology. These results are obtained by exploiting
interesting interactions between DGAs and stable homotopy theory. I am
going to start my talk by stating these classification results. For
the rest of the talk, I am going to present how stable homotopy theory
comes into play for the classification of DGAs. This presentation is
going to be accessible to a general audience.</p></div>Haldun Özgür Bayindir https://sites.google.com/view/ozgurbayindir/homeHaifatag:www.math.bgu.ac.il,2005:MeetingDecorator/5792019-10-23T11:24:29+03:002019-11-11T17:16:16+02:00<span class="mathjax">Hengfei Lu: The Prasad conjecture</span>November 27, 15:10—16:25, 2019, -101<div class="mathjax"><p>Period Problem is one of the most popular interesting problems in recent years, such as the Gan-Gross-Prasad conjectures. In this talk, we mainly focus on the local period problems, so called the relative Langlands programs. Given a quadratic local field extension E/F and a quasi-split reductive group G defined over F with associated quadratic character <span class="kdmath">$\chi_G$</span>, let <span class="kdmath">$\pi$</span> be an irreducible admissible representation of G(E). Assume the Langlands-Vogan conjecture. Dipendra Prasad uses the enhanced L-parameter of <span class="kdmath">$\pi$</span> to give a precise description for the multiplicity <span class="kdmath">$\dim Hom_{G(F)}(\pi,\chi_G)$</span> if the L-packet <span class="kdmath">$\Pi_\pi$</span> contains a generic representation. Then we can verify this conjecture if G=GSp(4).</p></div>Hengfei Luhttp://www.wisdom.weizmann.ac.il/~/hengfei/Weizmanntag:www.math.bgu.ac.il,2005:MeetingDecorator/5712019-10-20T10:55:34+03:002019-12-01T21:10:06+02:00<span class="mathjax">Ehud de Shalit : The Loxton - van der Poorten conjecture, and an elliptic analogue</span>December 4, 15:00—16:15, 2019, -101<div class="mathjax"><p>The conjecture of Loxton and var der Poorten is a criterion for a formal power series
to be the expansion at 0 of a rational function, and is related to a famous theorem of Cobham
in the theory of finite automata. It was proved by Adamczewski and Bell in 2013. Recently,
Schafke and Singer found a novel approach that lead also to a simple conceptual proof of
Cobham’s theorem. We shall explain these results and the cohomological machinery
behind them, and discuss what is missing from the picture to establish an elliptic analogue.</p></div>Ehud de Shalit http://www.math.huji.ac.il/~deshalit/new_site/default.htmHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/5722019-10-20T10:59:03+03:002019-12-02T17:42:11+02:00<span class="mathjax">Ariel Weiss: Irreducibility of Galois representations associated to low weight Siegel modular forms</span>December 11, 15:00—16:15, 2019, -101<div class="mathjax"><p>If f is a cuspidal modular eigenform of weight k>1, Ribet proved that its associated p-adic Galois representation is irreducible for all primes. More generally, it is conjectured that the p-adic Galois representations associated to cuspidal automorphic representations of GL(n) should always be irreducible.</p>
<p>In this talk, I will prove a version of this conjecture for <em>low weight, genus 2 Siegel modular forms</em>. These two-dimensional analogues of weight 1 modular forms are, conjecturally, the automorphic objects that correspond to abelian surfaces.</p></div>Ariel Weisshttp://ariel-weiss.postgrad.shef.ac.uk/HUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/5802019-10-23T11:26:38+03:002019-12-17T12:38:22+02:00<span class="mathjax">Amnon Yekutieli: Flatness and Completion Revisited</span>December 18, 15:00—16:15, 2019, -101<div class="mathjax"><p>https://www.math.bgu.ac.il/~amyekut/lectures/flat-comp-revis/abstract.html</p></div>Amnon Yekutielihttps://www.math.bgu.ac.il/~amyekut/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5732019-10-20T11:11:58+03:002019-12-23T11:57:27+02:00<span class="mathjax">Nadya Gurevich: Fourier transforms on the basic affine space</span>December 25, 15:00—16:15, 2019, -101<div class="mathjax"><p>For a quasi-split group $G$ over a local field $F$, with Borel subgroup $B=TU$ and Weyl group $W$,
there is a natural geometric action of $G\times T$ on $L^2(X),$ where $X=G/U$ is the basic affine space of $G$.
For split groups, Gelfand and Graev have extended this action to an action of
$G\times (T\rtimes W)$ by generalized Fourier transforms $\Phi_w$. We shall extend this result for quasi-split groups, using a new interpretation
of Fourier transforms for quasi-split groups
of rank one.</p>
<p>This is joint work with David Kazhdan.</p></div>Nadya Gurevichhttps://www.math.bgu.ac.il/~ngur/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5742019-10-20T11:13:48+03:002019-12-29T18:43:48+02:00<span class="mathjax">Ari Shnidman: Monogenic cubic fields and local obstructions</span>January 1, 15:00—16:15, 2020, -101<div class="mathjax"><p>A number field is monogenic if its ring of integers is generated by a single element. It is conjectured that 0% of degree d number fields are monogenic (for any d > 2). There are local obstructions that force this proportion to be < 100%, but beyond this very little is known. I’ll discuss work with Alpoge and Bhargava showing that a positive proportion of cubic fields (d = 3) have no local obstructions and yet are still not monogenic. This uses new results on integral points and ranks of Selmer groups of elliptic curves in twist families.</p></div>Ari Shnidmanhttp://math.huji.ac.il/~shnidman/HUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/5752019-10-20T11:15:59+03:002020-01-06T17:49:42+02:00<span class="mathjax">Ilya Tyomkin: Irreducibility problem for Severi varieties</span>January 8, 15:00—16:15, 2020, -101<div class="mathjax"><p>Severi varieties parameterize reduced irreducible curves of given geometric genus in a given linear system on an algebraic surface. The first irreducibility result for Severi varieties was established in 1986, and it is due to Harris, who considered the classical case of planar curves in characteristic zero. Few more irreducibility results have been obtained since then, but none of the known approaches is applicable in positive characteristic. In my talk, I will discuss the history and the state of the art in the irreducibility problem, and will also announce new results obtained in a joint work with Karl Christ and Xiang He.</p></div>Ilya Tyomkinhttps://www.math.bgu.ac.il/en/people/users/christkBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5762019-10-20T11:16:36+03:002020-01-06T17:45:38+02:00<span class="mathjax">Karl Christ: Degenerating plane curves via tropicalization</span>January 15, 15:00—16:15, 2020, -101<div class="mathjax"><p>In my talk, I will describe how simultaneous stable reduction and tropical geometry can be used to construct degenerations of plane curves. This is the main ingredient in a new proof for irreducibility of Severi varieties of the projective plane. The crucial feature of this construction is that it works in positive characteristic, where the other known methods fail. The talk will be a follow up on last week’s talk and is based on joint work with Xiang He and Ilya Tyomkin.</p></div>Karl ChristBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/5812019-10-23T11:27:46+03:002020-01-16T12:10:33+02:00<span class="mathjax">Amnon Yekutieli: Commutative DG Rings and their Derived Categories</span>January 22, 15:00—16:15, 2020, -101<div class="mathjax"><p>The commutative DG rings in the title are more commonly known as “nonpositive strongly commutative unital differential graded cochain K-algebras”, where K is a commutative base ring. In the literature the standard assumption is that K is a field of characteristic zero - but one of our themes in this talk is that this assumption is superfluous (K = Z works just as well).</p>
<p>There are two kinds of derived categories ralated to commutative DG rings. First, given a DG ring A, we can consider D(A), the derived category of DG A-modules, which is a K-linear triangulated category. This story is well understood by now, and I will only mention it briefly.</p>
<p>In this talk we shall consider another kind of derived category. Let DGRng denote the category whose objects are the commutative DG rings (the base K is implicit), and whose morphisms are the DG ring homomorphisms. The derived category of commutative DG rings is the category D(DGRng) gotten by inverting all the quasi-isomorphisms in DGRng. (In homotopy theory the convention is to call it the “homotopy category”, but this is an unfortunate historical accident.)</p>
<p>I will define semi-free DG rings, and prove their existence and lifting properties. Then I will introduce the quasi-homotopy relation on DGRng, giving rise to the quotient category K(DGRng), the “genuine” homotopy category. One of the main results is that the canonical functor from K(DGRng) to D(DGRng) is a faithful right Ore localization.</p>
<p>I will conclude with a theorem on the existence of the left derived tensor product inside D(DGRng), and with the pseudofunctor from D(DGRng) to the TrCat, sending a DG ring A to the triangulated category D(A).</p>
<p>Next semester I will talk about the geometrization of these ideas: “The Derived Category of Sheaves of Commutative DG Rings”.</p></div>Amnon Yekutielihttps://www.math.bgu.ac.il/~amyekut/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/6272020-02-07T19:56:04+02:002020-02-07T19:56:21+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6282020-02-07T19:56:33+02:002020-03-17T11:22:41+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6292020-02-07T19:57:33+02:002020-03-11T22:42:39+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6302020-02-07T19:58:10+02:002020-03-21T22:11:56+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6312020-02-07T19:59:14+02:002020-02-07T19:59:14+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6322020-02-07T19:59:33+02:002020-02-07T19:59:41+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6332020-02-07T20:08:50+02:002020-02-07T20:08:50+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6342020-02-07T20:09:43+02:002020-02-07T20:09:43+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6352020-02-07T20:09:58+02:002020-02-23T17:35:46+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6362020-02-07T20:49:59+02:002020-02-07T20:50:46+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6372020-02-07T20:51:04+02:002020-03-21T22:13:36+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6382020-02-07T20:54:48+02:002020-02-23T18:01:40+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6392020-02-07T20:55:15+02:002020-05-31T12:23:32+03:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6402020-02-07T20:55:43+02:002020-02-07T20:55:43+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6412020-02-07T20:56:11+02:002020-02-23T18:01:27+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6422020-02-07T20:57:04+02:002020-02-07T20:57:04+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/6432020-02-07T20:57:27+02:002020-02-23T18:03:58+02:00tag:www.math.bgu.ac.il,2005:MeetingDecorator/8152021-10-24T16:11:11+03:002021-10-24T16:15:13+03:00<span class="mathjax">none: TBA</span>October 27, 16:00—17:15, 2021, -101nonetag:www.math.bgu.ac.il,2005:MeetingDecorator/8142021-10-24T16:10:34+03:002021-10-25T18:44:45+03:00<span class="mathjax">Ariel Weiss: Prime torsion in the Tate-Shafarevich groups of abelian varieties over $\mathbb{Q}$</span>November 3, 16:00—17:15, 2021, -101<div class="mathjax"><p>Very little is known about the Tate-Shafarevich groups of abelian varieties. On the one hand, the BSD conjecture predicts that they are finite. On the other hand, heuristics suggest that, for each prime $p$, a positive proportion of elliptic curves $E/\mathbb{Q}$ have $\Sha(E)[p] \ne 0$, and one expects something similar for higher dimensional abelian varieties as well. Yet, despite these expectations, it seems to be an open question whether, for each prime $p$, there exists even a single elliptic curve over $\mathbb{Q}$ with $\Sha(E)[p] \ne 0$. In this talk, I will show that, for each prime $p$, there exists a geometrically simple abelian variety $A/\mathbb{Q}$ with $\Sha(A)[p]\ne 0$. Our examples arise from modular forms with Eisenstein congruences. This is joint work with Ari Shnidman.</p></div>Ariel Weisshttp://www.math.huji.ac.il/~arielweiss/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8162021-10-24T16:12:28+03:002021-11-08T10:04:19+02:00<span class="mathjax">Ariyan Javanpeykar: Rational points on ramified covers of abelian varieties, online lecture</span>November 10, 16:00—17:15, 2021, -101<div class="mathjax"><p>Let X be a ramified cover of an abelian variety A over a number field k. According to Lang’s conjecture, the k-rational points of X should not be dense. In joint work with Corvaja, Demeio, Lombardo, and Zannier, we prove a slightly weaker statement. Namely, assuming A(k) is dense, we show that the complement of the image of X(k) in A(k) is (still) dense, i.e., there are less points on X than there are on A (or: there are more points on A than on X). In this talk I will explain how our proof relies on interpreting this as a special case of a version of Hilbert’s irreducibility theorem for abelian varieties.</p></div>Ariyan Javanpeykarhttps://www.agtz.mathematik.uni-mainz.de/arakelov-geometrie/junior-prof-dr-ariyan-javanpeykar/Meinztag:www.math.bgu.ac.il,2005:MeetingDecorator/8172021-10-24T16:13:34+03:002021-11-17T14:59:22+02:00<span class="mathjax">No talk: TBA</span>November 17, 16:00—17:15, 2021, -101<div class="mathjax"><p><strong>strong text</strong></p></div>No talktag:www.math.bgu.ac.il,2005:MeetingDecorator/8182021-10-24T16:16:10+03:002021-11-22T11:33:52+02:00<span class="mathjax">David Corwin: Quadratic Chabauty and Beyond</span>November 24, 16:00—17:15, 2021, -101<div class="mathjax"><p>I will describe my work (some joint with I. Dan-Cohen) to extend the computational boundary of Kim’s non-abelian Chabauty’s method. 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. We first review classical Chabauty-Coleman, which does the same but works only for certain curves. Then we describe Kim’s non-abelian generalization, which replaces abelian varieties in Chabauty-Coleman by Selmer groups (a kind of Galois cohomology) and eventually “non-abelian” Selmer varieties. Finally, we describe recent work in attempting to compute these sets using the theory of Tannakian categories.</p></div>David Corwinhttps://math.berkeley.edu/~dcorwin/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8192021-10-24T16:17:48+03:002021-10-24T16:17:48+03:00<span class="mathjax">Sa’ar Zehavi: TBA</span>December 1, 16:00—17:15, 2021, -101Sa'ar ZehaviTAUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8222021-10-25T18:56:45+03:002021-12-06T23:10:50+02:00<span class="mathjax">David Ter-Borch Gram Lilienfeldt: Experiments with Ceresa classes of cyclic Fermat quotients</span>December 8, 16:00—17:15, 2021, -101<div class="mathjax"><p>We give two new examples of non-hyperelliptic curves whose Ceresa cycles have torsion images in the intermediate Jacobian. For one of them, we find that the central value of the L-function of the relevant motive is non-vanishing, consistent with the conjectures of Beilinson and Bloch. We speculate on a possible explanation for the existence of these torsion Ceresa classes, based on some computations with cyclic Fermat quotients. This is joint work with Ari Shnidman.</p></div>David Ter-Borch Gram Lilienfeldthttps://math.huji.ac.il/~lilienfeldt/HUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/8232021-10-25T18:57:43+03:002021-12-13T09:45:45+02:00<span class="mathjax">Dmitry Kerner: Finite determinacy of maps. Group orbits vs the tangent spaces</span>December 15, 16:00—17:15, 2021, -101<div class="mathjax"><p>Consider a morphism of germs of Noetherian schemes, f: (X,x)-> (Y,y). When is it ‘stable’ under perturbations by higher order terms? I.e. when can such a perturbation be undone by a group action, e.g. by the local coordinate changes.
This question has been extensively studied for real/complex analytic (or C^k) maps
(k^n,o)-> (k^m,o). The idea is to reduce the orbit study, Gf, to the study of the tangent space, T_G f.
The classical methods used vector field integration and infinite dimensional Lie groups, thus obstructing extensions to the zero/positive characteristic. During the last years we have developed a purely algebraic approach to this problem, extending the results to arbitrary characteristic.
The key tool is the ‘Lie-type pair’. This is a group G, its would-be tangent space T_G, and certain maps between G, T_G, approximating the classical exponential/logarithm.</p>
<p>(joint work with G. Belitskii, A.F. Boix, G.M. Greuel.)</p></div>Dmitry Kernerhttps://www.math.bgu.ac.il/~kernerdm/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8242021-10-25T18:58:39+03:002021-12-13T09:52:04+02:00<span class="mathjax">Ido Efrat: Filtrations of profinite groups as intersections and absolute Galois groups</span>December 22, 16:00—17:15, 2021, -101<div class="mathjax"><p>The general structure of absolute Galois groups of fields as profinite groups is still a mystery. Among the very few
known properties of such groups are several “Intersection Theorems”, describing subgroups in standard filtrations
of absolute Galois groups as the intersection of all normal open subgroups with quotient in a prescribed list of
finite groups. These theorems are based on deep cohomological properties of absolute Galois groups. We will
present a general “Transfer Theorem” for profinite groups, which explains what lies behind these intersection
theorems.</p></div>Ido Efrathttps://www.math.bgu.ac.il/~efrat/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8552021-12-06T23:19:19+02:002021-12-06T23:19:19+02:00<span class="mathjax">Amit Ophir: TBA</span>December 29, 16:00—17:15, 2021, -101Amit OphirHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/8562021-12-06T23:20:45+02:002022-01-04T10:50:08+02:00<span class="mathjax">Daniel Disegni: Theta cycles</span>January 5, 16:00—17:15, 2022, -101<div class="mathjax"><p>I will discuss results and open problems in an emerging theory of ‘canonical’ algebraic cycles for all motives enjoying a certain symmetry. The construction is inspired by theta series, and based on special subvarieties in arithmetic quotients of the complex unit ball.
The ‘theta cycles’ seem as pleasing as Heegner points on elliptic curves: (1) their nontriviality is detected by derivatives of complex or p-adic L-functions; (2) if nontrivial, they generate the Selmer group of the motive. This supports analogues of the Birch and Swinnerton-Dyer conjecture. I will focus on (2), whose proof combines the method of Euler systems and the local theta correspondence in representation theory.</p></div>Daniel Disegnihttps://disegni-daniel.perso.math.cnrs.fr/index.htmlBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8132021-10-24T16:08:05+03:002021-10-24T16:08:05+03:00<span class="mathjax">: TBA</span>March 2, 16:00—17:15, 2022, -101tag:www.math.bgu.ac.il,2005:MeetingDecorator/8712022-03-24T15:05:32+02:002022-03-24T15:06:16+02:00<span class="mathjax">Bogdan Adrian Dina: Isogenous (non-)hyperelliptic CM Jacobians: constructions, results, and Shimura class groups. (-101)</span>March 30, 16:00—17:15, 2022, -101<div class="mathjax"><p>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) list of such isogenous Jacobians. This talk describes the main constructions, some results, and Shimura class groups.</p></div>Bogdan Adrian DinaHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/8722022-03-24T15:09:32+02:002022-04-04T10:22:54+03:00<span class="mathjax">No talk: TBA</span>April 6, 16:00—17:15, 2022, -101No talktag:www.math.bgu.ac.il,2005:MeetingDecorator/8732022-03-24T15:11:32+02:002022-03-24T15:11:32+02:00<span class="mathjax">No meeting: TBA</span>April 13, 16:00—17:15, 2022, -101No meetingtag:www.math.bgu.ac.il,2005:MeetingDecorator/8742022-03-24T15:13:13+02:002022-03-24T15:13:13+02:00<span class="mathjax">No meeting: TBA</span>April 20, 16:00—17:15, 2022, -101No meetingtag:www.math.bgu.ac.il,2005:MeetingDecorator/8752022-03-24T15:16:15+02:002022-04-25T20:29:48+03:00<span class="mathjax">Amnon Yekutieli: A Constructive Approach to Derived Algebra, online meeting</span>April 27, 16:00—17:00, 2022, -101<div class="mathjax"><p>In the last twenty years algebraic geometry has evolved rapidly, from the geometry of schemes and stacks, to the derived algebraic geometry (DAG) of today. The flavor of contemporary DAG is very homotopical, in the sense that is largely based on simplicial sets and Quillen model structures.</p>
<p>This talk is on another approach to DAG, of a very algebraic flavor, which avoids simplicial methods and model structures altogether. Instead, the fundamental concept is that of DG rings, traditionally called unital associative cochain DG algebras. DG rings are of two distinct kinds: noncommutative and commutative. These two kinds of DG rings interact, primarily through central DG ring homomorphisms; and this interaction is quite fruitful. The main tool for studying DG rings, DG modules over them, and the associated derived categories, is the construction and manipulation of resolutions. Hence “constructive approach”.</p>
<p>I will define the notions mentioned above, and state several results, among them: (1) The squaring operation and Van den Bergh’s rigid dualizing complexes in the commutative arithmetic setting; (2) Theorems on derived Morita theory; (3) Duality and tilting for commutative DG rings. I will try to demonstrate that this constructive approach is very amenable to calculation. I will also mention work of Shaul, within this framework, on derived completion of DG rings and on the derived CM property.</p>
<p>The talk will conclude with a couple of conjectural ideas: (a) A structural description of the derived category of DG categories; (b) A construction of the cotangent DG module within the framework of commutative DG rings, without any arithmetic restrictions.</p>
<p>Some of this work is joint with J. Zhang, L. Shaul, M. Ornaghi and S. Singh.</p>
<p>Slides for the talk are available here:</p>
<p>https://sites.google.com/view/amyekut-math-bgu/home/lectures/constr-der-algebra</p>
<p>(updated 15 March 2022)</p></div>Amnon Yekutielihttps://www.math.bgu.ac.il/~amyekut/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8762022-03-24T15:17:05+02:002022-03-24T15:17:05+02:00<span class="mathjax">No meeting: TBA</span>May 4, 16:00—17:15, 2022, -101No meetingtag:www.math.bgu.ac.il,2005:MeetingDecorator/8772022-03-24T15:18:52+02:002022-05-08T11:50:10+03:00<span class="mathjax">Paolo Dolce: Introduction to Diophantine approximation and a generalisation of Roth’s theorem</span>May 11, 16:00—17:00, 2022, -101<div class="mathjax"><p>Classically, Diophantine approximation deals with the problem of studying “good” approximations of a real number by rational numbers. I will explain the meaning of “good approximants” and the classical main results in this area of research. In particular, Klaus Roth was awarded with the Fields medal in 1955 for proving that the approximation exponent of a real algebraic number is 2. I will present a recent extension of Roth’s theorem in the framework of adelic curves. These mathematical objects, introduced by Chen and Moriwaki in 2020, stand as a generalisation of global fields.</p></div>Paolo Dolcehttps://www.paolodolce.com/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8782022-03-24T15:19:22+02:002022-05-12T12:20:49+03:00<span class="mathjax">Amit Ophir: Ribet’s lemma for GL_2 modulo prime powers</span>May 18, 16:00—17:00, 2022, -101<div class="mathjax"><p>Ribet’s lemma is an algebraic statement that Ribet used in his proof of the converse of Herbrand’s theorem. Since then various generalisations of Ribet’s lemma have been found, with arithmetic applications. In this talk I will discuss a joint work with Ariel Weiss in which we show that two measures of reducibility for two dimensional representations over a DVR are the same, thus answering a question of Bellaiche and Cheneveier, and deducing from it a particular generalisation of Ribet’s lemma. An interesting feature of the proof is that it applies to both the residually multiplicity-free and the residually non-multiplicity-free cases. I will discuss an application to a local-global principle for isogenies of elliptic curves.</p></div>Amit OphirHUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/8792022-03-24T15:19:55+02:002022-05-23T17:21:11+03:00<span class="mathjax">David Corwin: Bloch-Kato Groups and Iwasawa Theory in Chabauty-Kim</span>May 25, 16:00—17:00, 2022, -101<div class="mathjax"><p>We explain different kinds of Selmer groups, which are subgroups of Galois cohomology, including Bloch-Kato, strict, and Greenberg Selmer groups. We state part of the Bloch-Kato conjectures and describe a bound joint with A. Betts and M. Leonhardt on the number of rational points on a general higher genus curve, conditional on the Bloch-Kato conjectures. Finally, we explain how to use some Iwasawa theory, specifically Kato’s Euler system and a control theorem of Ochiai, to deduce specific cases of Bloch-Kato associated with elliptic curves.</p></div>David CorwinBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/8802022-03-24T15:20:30+02:002022-05-31T15:47:11+03:00<span class="mathjax">Daniil Rudenko (online meeting): Volumes of Hyperbolic Polytopes, Cluster Polylogarithms, and the Goncharov Depth Conjecture</span>June 1, 16:00—17:00, 2022, -101<div class="mathjax"><p>Lobachevsky started to work on computing volumes of hyperbolic polytopes long before the first model of the hyperbolic space was found. He discovered an extraordinary formula for the volume of an orthoscheme via a special function called dilogarithm.</p>
<p>We will discuss a generalization of the formula of Lobachevsky to higher dimensions. For reasons I do not fully understand, a mild modification of this formula leads to the proof of a conjecture of Goncharov about the depth of multiple polylogarithms. Moreover, the same construction leads to a functional equation for polylogarithms generalizing known equations of Abel, Kummer, and Goncharov.</p>
<p>Guided by these observations, I will define cluster polylogarithms on a cluster variety.</p></div>Daniil Rudenko (online meeting)http://math.uchicago.edu/~rudenkodaniil/Chicagotag:www.math.bgu.ac.il,2005:MeetingDecorator/8812022-03-24T15:20:38+02:002022-04-23T10:19:33+03:00<span class="mathjax">Daniil Rudenko (online meeting): TBA</span>June 8, 16:00—17:00, 2022, -101Daniil Rudenko (online meeting)Chicagotag:www.math.bgu.ac.il,2005:MeetingDecorator/8822022-03-24T15:20:50+02:002022-04-23T10:19:49+03:00<span class="mathjax">Jakob Scholbach (online meeting): Arakelov motivic cohomology</span>June 15, 16:00—17:00, 2022, -101<div class="mathjax"><p>Jakob has kindly agreed to speak about his old work on Arakelov motivic cohomology and comparison with the arithmetic intersection pairing of Gillet-Soul'e.</p></div>Jakob Scholbach (online meeting)https://ivv5hpp.uni-muenster.de/u/jscho_04/Munstertag:www.math.bgu.ac.il,2005:MeetingDecorator/8962022-06-16T10:49:52+03:002022-06-16T10:49:52+03:00<span class="mathjax">Anton Khoroshkin: Graph complex and deformations of quadratic Poisson structures</span>June 22, 14:10—15:10, 2022, -101<div class="mathjax"><p>A universal deformation of Poisson structures was constructed by M.Kontsevich in 90’s.
D.Tamarkin explained that the set of universal deformations are in one-to-one correspondence with Drinfeld Associators.
On the other hand, we know that all universal deformations of linear Poisson structures are trivial and coincide with universal enveloping algebra.
We show that universal deformations of quadratic Poisson structure are as rich as the full set of all deformations.</p>
<p>The first part of the talk will be devoted to the elementary description of Kontsevich Graph complexes and related combinatorics.
The relationships with the universal quantization problems of generic and quadratic Poisson structures will be given in the second part of the talk (based on the joint results with Sergei Merkulov https://arxiv.org/abs/2109.07793).</p></div>Anton Khoroshkinhttps://sites.google.com/site/akhoroshkin/Higher School of Economics (Moscow)tag:www.math.bgu.ac.il,2005:MeetingDecorator/8832022-03-24T15:21:16+02:002022-06-16T10:50:26+03:00<span class="mathjax">Qirui Li (online meeting): The linear AFL for non-basic locus</span>June 22, 16:00—17:00, 2022, -101<div class="mathjax"><p>The Arithmetic Fundamental Lemma (AFL) is a local conjecture motivated by decomposing both sides of the Gross—Zagier Formula into local terms using the Relative Trace formula. For each of the local terms, one side is the intersection number in some Rappoport—Zink space. The other side is some orbital integral. To reduce the global computation to local, one needs to consider intersection numbers on both basic and non-basic locus, while the original linear AFL only considers basic locus.</p>
<p>Collaborated with Andreas Mihatsch, we consider the non-basic locus of Unitary Shimura varieties and conjectured a similar version of linear AFL for Rappoport Zink space on non-basic locus parameterizing p-divisible groups with étale extensions. We proved that this version of linear AFL conjecture can be essentially reduced to the linear AFL conjecture for Lubin—Tate spaces, which corresponds to the basic locus parameterizing one-dimensional connected p-divisible groups.</p></div>Qirui Li (online meeting)http://qirui.liBonntag:www.math.bgu.ac.il,2005:MeetingDecorator/8842022-03-24T15:21:26+02:002022-06-18T14:08:57+03:00<span class="mathjax">Ishai Dan-Cohen: <em>p</em>-Adic periods and Selmer scheme images</span>June 29, 16:00—17:00, 2022, -101<div class="mathjax"><p>The category of mixed Tate motives over an open integer ring or a number field possesses a notion of <em>p</em>-adic period which diverges somewhat from the complex paradigm: rather than comparing two different fiber functors, it compares two different structures both associated with the same cohomology theory. At first glance, it appears to be a peculiarity of the mixed Tate setting. Yet it plays a central role in the microcosm of mixed Tate Chabauty-Kim. It also connects the study of <em>p</em>-adic iterated integrals with Goncharov’s theory of <em>motivic</em> iterated integrals, and allows us to investigate Goncharov’s conjectures from a <em>p</em>-adic point of view. Lastly, it forms the basis for the so-called <em>p</em>-adic period conjecture. I’ll report on our ongoing work devoted to the construction of <em>p</em>-adic periods beyond the mixed Tate setting, and discuss the possibility of generalizing all aspects of this picture. This is joint work with David Corwin.</p></div>Ishai Dan-Cohenhttps://www.math.bgu.ac.il/~ishaida/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/9232022-10-20T13:29:35+03:002022-10-20T13:29:35+03:00<span class="mathjax">Nadav Gropper: Surfaces and p-adic fields</span>October 25, 12:00—13:00, 2022, -101<div class="mathjax"><p>The philosophy of arithmetic topology, first established by Mazur, gives an analogy relating arithmetic to lower dimensional topology. Under this philosophy, one gets a dictionary, relating between Number fields and 3-manifolds, primes and knots, and p-adic fields and surfaces.
In the talk I will try and explain why these surprising analogies were drawn. I will also outline some recent work of the speaker, which further establishes this connection for the local case, using tools such as graphs of groups and Bass–Serre theory.</p></div>Nadav GropperBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/9242022-10-20T13:36:32+03:002022-11-08T12:06:40+02:00<span class="mathjax">Yotam Hendel: On uniform number theoretic estimates for fibers of polynomial maps over finite rings of the form Z/p^kZ</span>November 8, 12:40—13:40, 2022, 201<div class="mathjax"><p>Let f:X \to Y be a morphism between smooth, geometrically irreducible Z-schemes of finite type.
We study the number of solutions #{x:f(x)=y mod p^k} for prime p, positive number k, and y \in Y(Z/p^kZ), and show that the geometry and singularities of the fibers of f determine the asymptotic behavior of this quantity as p, k and y vary.</p>
<p>In particular, we show that f:X \to Y is flat with fibers of rational singularities, a property abbreviated (FRS), if and only if #{x:f(x)=y mod p^k}/p^{k(\dim X -\dim Y)} is uniformly bounded in p, k and y. We then consider a natural family of singularity properties, which are variants of the (FRS) property, and provide for each member of this family a number theoretic characterization using the asymptotics of #{x:f(x)=y mod p^k}/p^{k(\dim X -\dim Y)}.</p>
<p>To prove our results, we use model theoretic tools (and in particular the theory of motivic integration, in the sense of uniform p-adic integration) to effectively study the collection {#{x:f(x)=y mod p^k}/p^{k(\dim X -\dim Y)}. If time allows, we will discuss these methods.</p>
<p>Based on a joint work with Raf Cluckers and Itay Glazer.</p></div>Yotam Hendelhttps://sites.google.com/view/yotam-hendelUniversité de Lilletag:www.math.bgu.ac.il,2005:MeetingDecorator/9252022-10-20T13:37:17+03:002022-11-13T13:37:24+02:00<span class="mathjax">Utkarsh Agrawal: Central values of degree six L-functions attached to two Hilbert modular newforms</span>November 15, 12:40—13:40, 2022, 201<div class="mathjax"><p>Let f,g be two Hilbert modular newforms (functions on ’n-copies’ of the upper half-plane, satisfying properties similar to usual modular forms). Consider the L-function L(s,f \times \Sym^{2}g) (it is the degree six factor of the triple product L-function L(s,f \times g \times g)). In this talk we will give a formula for the central value of this L-function and work out its rationality in some special cases of relationships between weights of f and g. We will arrive at our formula via the refined Gan-Gross-Prasad formula for SL(2) \times \tilde(SL(2)). Our results on rationality are compatible with Deligne’s conjecture on the rationality of critical values of motivic L-functions.</p></div>Utkarsh AgrawalBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/9332022-11-13T13:39:01+02:002022-11-13T13:39:01+02:00<span class="mathjax">Nadav Gropper: Continuation of previous talk</span>November 22, 12:40—13:40, 2022, -101Nadav GropperBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/9462022-11-23T15:15:31+02:002022-11-23T15:15:31+02:00<span class="mathjax">Paolo Dolce: Numerical equivalence of R-divisors and Shioda-Tate formula for arithmetic varieties</span>November 29, 12:40—13:40, 2022, -101<div class="mathjax"><p>Arakelov geometry offers a framework to develop an arithmetic counterpart of the usual intersection theory. For varieties defined over the ring of integers of a number field, and inspired by the geometric case, one can define a suitable notion of arithmetic Chow groups and of an arithmetic intersection product. In a joint work with Roberto Gualdi (University of Regensburg), we prove an arithmetic analogue of the classical Shioda-Tate formula, relating the dimension of the first Arakelov-Chow vector space of an arithmetic variety to some of its geometric invariants. In doing so, we also characterize numerically trivial arithmetic divisors, confirming part of a conjecture by Gillet and Soulé.</p></div>Paolo Dolcehttps://www.paolodolce.com/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/9342022-11-13T13:40:23+02:002022-11-23T15:13:59+02:00<span class="mathjax">Yotam Hendel: Continuation of previous talk, online meeting</span>December 6, 12:40—13:40, 2022, 201Yotam Hendeltag:www.math.bgu.ac.il,2005:MeetingDecorator/9352022-11-13T14:00:12+02:002022-12-08T13:31:38+02:00<span class="mathjax">Haining Wang, online meeting: Arithmetic level raising for GSp(4)</span>December 13, 12:40—13:40, 2022, 000<div class="mathjax"><p>Level raising theorems for modular forms are theorems about congruences of modular forms between different levels. These theorems play an important role in the proof of the Fermat’s last theorem by Wiles. In this talk, we will report some recent work on realizing level raising theorems for automorphic forms on GSp(4) by studying the geometry of certain quaternionic unitary Shimura variety.</p></div>Haining Wang, online meetinghttps://wanghaining11.github.ioShanghai Center for Mathematical Sciences, Fudan Universitytag:www.math.bgu.ac.il,2005:MeetingDecorator/9362022-11-13T14:01:37+02:002022-12-08T17:51:50+02:00<span class="mathjax">Yotam Svoray: Invariants on non-isolated hypersurface singularities</span>December 20, 12:40—13:40, 2022, -101<div class="mathjax"><p>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 hypersurfaces 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 regarding morsifications of such singularities. In addition, we will present some applications to the study of Yomdin-type isolated singularities.</p></div>Yotam SvorayUniversity of Utahtag:www.math.bgu.ac.il,2005:MeetingDecorator/9372022-11-13T14:02:55+02:002022-12-20T15:13:21+02:00<span class="mathjax">Liran Shaul: Finitistic dimensions, DG-rings and dualizing complexes</span>December 27, 12:40—13:40, 2022, -101<div class="mathjax"><p>The projective finitistic dimension of a ring is an important homological dimension which measures the complexity of homological algebra over it.
The finitistic dimension conjecture which says that this invariant is finite for artin algebras is considered to be one of the most important open problems in homological algebra.
In this talk we discuss this conjecture, its importance and connection to other important conjectures.
We then show how by using DG-ring techniques, and the noncommutative covariant Grothendieck duality,
it is possible to connect this conjecture to the global structure of injective modules in the unbounded derived category of the ring.
This generalizes work of Rickard from finite dimensional algebras over a field to all noetherian rings which admit a dualizing complex.</p></div>Liran Shaulhttps://liranshaul.wordpress.comCharles University, Praguetag:www.math.bgu.ac.il,2005:MeetingDecorator/9382022-11-13T14:03:47+02:002022-12-26T20:09:38+02:00<span class="mathjax">TBA: TBA</span>January 3, 12:40—13:40, 2023, -101TBAtag:www.math.bgu.ac.il,2005:MeetingDecorator/9392022-11-13T14:04:20+02:002023-01-09T08:39:59+02:00<span class="mathjax">Adam Logan: A conjectural uniform construction of many rigid Calabi-Yau threefolds</span>January 10, 15:00—16:00, 2023, -101<div class="mathjax"><p>Given a rational Hecke eigenform $f$ of weight $2$, Eichler-Shimura theory gives a construction of an elliptic curve over ${\mathbb Q}$ whose associated modular form is $f$. Mazur, van Straten, and others have asked whether there is an analogous construction for Hecke eigenforms $f$ of weight $k>2$ that produces a variety for which the Galois representation on its etale ${\mathrm H}^{k-1}$ (modulo classes of cycles if $k$ is odd) is that of $f$. In weight $3$ this is understood by work of Elkies and Sch"utt, but in higher weight it remains mysterious, despite many examples in weight $4$. In this talk I will present a new construction based on families of K3 surfaces of Picard number $19$ that recovers many existing examples in weight $4$ and produces almost $20$ new ones.</p></div>Adam Loganhttps://www.math.uwaterloo.ca/~a5logan/math/index.htmlMcGilltag:www.math.bgu.ac.il,2005:MeetingDecorator/9402022-11-13T14:07:25+02:002023-01-16T16:31:16+02:00<span class="mathjax">Martin Lüdtke, online meeting: Non-abelian Chabauty for the thrice-punctured line and the Selmer section conjecture</span>January 17, 12:40—13:40, 2023, 666<div class="mathjax"><p>For a smooth projective hyperbolic curve Y/Q the set of rational points Y(Q) is finite by Faltings’ Theorem. Grothendieck’s section conjecture predicts that this set can be described via Galois sections of the étale fundamental group of Y. On the other hand, the non-abelian Chabauty method produces p-adic analytic functions which conjecturally cut out Y(Q) as a subset of Y(Qp). We relate the two conjectures and discuss the example of the thrice-punctured line, where non-abelian Chabauty is used to prove a local-to-glocal principle for the section conjecture.</p></div>Martin Lüdtke, online meetinghttps://www.rug.nl/staff/m.w.ludtke/?lang=enGroningentag:www.math.bgu.ac.il,2005:MeetingDecorator/9862023-03-21T10:35:41+02:002023-03-21T10:40:23+02:00<span class="mathjax">Amnon Yekutieli: An Algebraic Approach to the Cotangent Complex (online meeting)</span>March 27, 12:10—13:10, 2023, -101<div class="mathjax"><p>Let $B/A$ be a pair of commutative rings. We propose an algebraic approach to the cotangent complex $L_{B/A}$. Using commutative semi-free DG ring resolutions of B relative to A, we construct a complex of $B$-modules $LCot_{B/A}$. This construction works more generally for a pair $B/A$ of commutative DG rings.</p>
<p>In the talk we will explain all these concepts. Then we will discuss the important properties of the DG $B$-module $LCot_{B/A}$. It time permits, we’ll outline some of the proofs.</p>
<p>It is conjectured that for a pair of rings $B/A$, our $LCot_{B/A}$ coincides with the usual cotangent complex $L_{B/A}$, which is constructed by simplicial methods. We shall also relate $LCot_{B/A}$ to modern homotopical versions of the cotangent complex.</p>
<p>Slides: https://sites.google.com/view/amyekut-math/home/lectures/cotangent</p></div>Amnon Yekutielihttps://www.math.bgu.ac.il/~amyekut/BGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/9942023-05-11T12:48:55+03:002023-05-14T13:32:04+03:00<span class="mathjax">George Papas: Some cases of the Zilber-Pink conjecture for curves in $\mathcal{A}_g$</span>May 29, 12:10—13:10, 2023, -101<div class="mathjax"><p>The Zilber-Pink conjecture is a far reaching and widely open conjecture in the field of unlikely intersections generalizing many previous results in the area such as the Andre-Oort conjecture. We discuss this conjecture and how some cases of it can be established for curves in $\mathcal{A}_g$, the moduli space of principally polarized g-dimensional abelian varieties, following the Pila-Zannier strategy and bounds for the values of the Weil height at certain exceptional points of the curve.</p></div>George Papashttps://sites.google.com/site/georgepappashomepage/home?pli=1HUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/9952023-05-11T12:53:32+03:002023-06-04T11:01:31+03:00<span class="mathjax">Hongjie Yu: l-Adic local systems and Higgs bundles</span>June 5, 12:10—13:10, 2023, -101<div class="mathjax"><p>In 1981, Drinfeld enumerated the number of irreducible l-adic local systems of rank two on a projective smooth curve in positive characteristic fixed by the Frobenius endomorphism. Interestingly, this number bears resemblance to the number of points on a variety over a finite field. Deligne proposed conjectures to extend and comprehend Drinfeld’s result. In this talk, I will present Deligne’s conjectures and discuss some mysterious phenomena that have emerged in various cases where this number is related to the number of stable Higgs bundles.</p></div>Hongjie Yuhttps://www.hongjieyu.comWeizmanntag:www.math.bgu.ac.il,2005:MeetingDecorator/9962023-05-11T12:56:15+03:002023-06-16T11:18:49+03:00<span class="mathjax">David Ter-Borch Gram Lilienfeldt: TBA</span>June 19, 12:10—13:10, 2023, -101<div class="mathjax"><p>The Gross-Zagier formula equates (up to an explicit non-zero constant) the central value of the first derivative of the Rankin-Selberg L-function of a weight 2 eigenform and the theta series of a class group character of an imaginary quadratic field (satisfying the Heegner hypothesis) with the height of a Heegner point on the corresponding modular curve. This equality is a key ingredient in the proof of the Birch and Swinnerton-Dyer conjecture for elliptic curves over the rationals in analytic rank 0 and 1. Two important generalizations present themselves: to allow eigenforms of higher weight, and to allow Hecke characters of infinite order. The former one is due to Shou-Wu Zhang. The latter one is the subject of a joint work in progress with Ari Shnidman and requires the calculation of the Beilinson-Bloch heights of generalized Heegner cycles. In this talk, I will report on the calculation of the archimedean local heights of these cycles.</p></div>David Ter-Borch Gram Lilienfeldthttps://math.huji.ac.il/~lilienfeldt/HUJItag:www.math.bgu.ac.il,2005:MeetingDecorator/10372024-02-05T06:12:59+02:002024-02-07T23:10:30+02:00<span class="mathjax">Amnon Besser: Quadratic Chabauty, p-adic adelic metrics and local contributions</span>February 7, 14:10—15:00, 2024, -101<div class="mathjax"><p>This talk is based on my ongoing work with Steffen Muller and Padma Srinivasan. I will explain the idea of the Quadratic Chabauty method for finding rational points on curves and how one reinterprets previous work by Balakrishnan and Dogra, on their own and with collaborators, using p-adic
adelic metrics on line bundles. Time permitting I will explain how one can use this to compute the “local contributions away from p” for Quadratic Chabauty, which are crucial for computations.</p></div>Amnon Besserhttps://www.math.bgu.ac.il//~besseraBGUtag:www.math.bgu.ac.il,2005:MeetingDecorator/10402024-02-11T12:12:24+02:002024-02-11T12:12:24+02:00<span class="mathjax">Amnon Besser: Quadratic Chabauty, p-adic adelic metrics and local contributions, Part II</span>February 14, 14:10—15:00, 2024, -101<div class="mathjax"><p>Continuing with the topics of last week’s talk, I will explain how one can use this to compute the “local contributions away from p” for Quadratic Chabauty, which are crucial for computations.</p></div>Amnon Besserhttp://www.math.bgu.ac.il/~besseraBen Gurion Universitytag:www.math.bgu.ac.il,2005:MeetingDecorator/10442024-02-27T08:41:32+02:002024-02-28T22:27:08+02:00<span class="mathjax">Jay Swar: Symplectic Geometry, Knot Invariants, and Selmer Spaces</span>February 28, 14:10—15:00, 2024, -101<div class="mathjax"><p>An effective approach to the Diophantine problem of enumerating all points on curves with non-abelian fundamental groups, such as those of genus greater than 1, is provided (conjecturally always) by the Chabauty-Kim method. The central object in this method is a Selmer scheme associated to the initial curve of interest and generalizing the association of Selmer groups to elliptic curves. In this talk, we’ll show that arithmetic dualities produce (derived) symplectic and Lagrangian structures on associated spaces which reflect certain expectations coming from “arithmetic topology”. In addition to some Diophantine utility, this should be viewed as foundational towards a “TQFT” approach to L-functions and related invariants analogous to a parallel story producing knot invariants from structures on character varieties which will be elaborated upon.</p></div>Jay SwarUniversity of Haifatag:www.math.bgu.ac.il,2005:MeetingDecorator/10452024-02-28T22:29:49+02:002024-02-28T22:29:49+02:00<span class="mathjax">Boris Bychkov: x-y duality in topological recursion, Hurwitz numbers and integrability</span>March 6, 14:10—15:00, 2024, -101<div class="mathjax"><p>Topological recursion is a remarkable universal recursive procedure that has been found in many enumerative geometry problems, from combinatorics of maps, to random matrices, Gromov-Witten invariants, Hurwitz numbers, Mirzakhani’s hyperbolic volumes of moduli spaces, knot polynomials. A recursion needs an initial data: a spectral curve, and the recursion defines the sequence of invariants of that spectral curve.
There is a duality in topological recursion which allows one to obtain closed formulas for the invariants of the recursion and which has implications in free probability theory and integrable hierarchies. In the talk I will survey recent progress in the topic with the examples from Hurwitz numbers theory, Hodge integrals and combinatorics of maps.</p>
<p>The talk is based on the joint works with A. Alexandrov, P. Dunin-Barkowski, M. Kazarian and S. Shadrin.</p></div>Boris BychkovHSE and Haifatag:www.math.bgu.ac.il,2005:MeetingDecorator/10422024-02-16T22:18:09+02:002024-02-20T17:20:04+02:00<span class="mathjax">Grigory Papayanov: Holomorphic Fedosov quantizations and the period map</span>March 13, 14:10—15:00, 2024, -101<div class="mathjax"><p>The Gelfand-Kazhdan formal geometry is a way of describing geometric structures on a smooth manifold M
in terms of the jet bundle. The works of Fedosov, Nest-Tsygan and Bezrukavnikov-Kaledin
put the problem of classifying deformation quantizations of, respectively, smooth, holomorphic and algebraic
symplectic manifolds into the context of formal geometry. They showed that, if the Hodge filtration
on the cohomology of the symplectic manifold splits, the set of deformation quantizations of M could be identified with a certain
subset of $H^2(M)[[h]]$ via the so-called period map. In the talk I want to describe an upgrade of the period map from
a map between sets to a morphism between suitably defined deformation functors. This upgrade could be used to
reprove the Fedosov-Nest-Tsygan-Bezrukavnikov-Kaledin theorems, to help classify quantizations
without the Hodge filtration splitting condition, and to connect the period map with the so-called Rozansky-Witten invariants.</p></div>Grigory PapayanovNorthwestern, visiting Weizmanntag:www.math.bgu.ac.il,2005:MeetingDecorator/10472024-03-10T15:23:53+02:002024-03-10T15:23:53+02:00<span class="mathjax">Eyal Goren: Supersingular elliptic curves, quaternion algebras and some applications to cryptography</span>May 29, 14:10—15:00, 2024, -101Eyal GorenMcGill University