Events for 03/05/2021 from all calendars

Seminar in Random Tensors

Time: 11:00AM - 12:00PM

Location: zoom

Speaker: Dan Mikulincer, Weizmann Institute

Title: A central limit theorem for tensor powers

Abstract: We introduce the Wishart tensor as the p'th tensor power of a given random vector X in R^n. This is inspired by the classical Wishart matrix, obtained when p = 2. Sums of independent Wishart tensors appear naturally in several settings, such as empirical moment tensors and random geometric graphs. We will discuss possible connections and recent results. The main focus of the talk will be quantitative estimates for the central limit theorem of Wishart tensors. In this setting, we will explain how Stein's method may be used to exploit the low dimensional structure which is inherent to tensor powers. Specifically, it will be shown that, under appropriate regularity assumptions, a sum of independent Wishart tensors is close to a Gaussian tensor as soon as n^(2p-1)

Teaching Online Departmental Open Forum

Time: 12:00PM - 1:00PM

Location: Zoom

Speaker: Vanessa Coffelt & Justin Cantu, Texas A&M University

Description: All forums will be from 12:00 pm to 1:00 pm. The topic will be emailed to faculty the week prior to the forum. We will use the following Meeting ID: 979 6560 9771, and will send out the password in the emails.

Noncommutative Geometry Seminar

Time: 1:00PM - 2:00PM

Location: Zoom 951 5490 42

Speaker: Claire Debord, Paris 7

Title: Cyclic subsets, groupoids and VB-groupoids

Abstract: In this talk, after recalling basic facts on groupoids, we will see that the structure of a groupoid G is entirely determined by giving invariant subsets by cyclic permutations of the Cartesian product G^k for k=0,…,3 and satisfying some additional properties. We will then focus our attention on a special type of groupoids, namely VB-groupoids and see how this point of view allows to find very simply the construction of the dual groupoid of a VB-groupoid. In particular, we recover the famous Weinstein’s cotangent groupoid. Finally, we will construct a Fourier transform in this situation which induces an isomorphism between the C*-algebra of a VB-groupoid E and the C*-algebra of the VB-groupoid dual E*. This is a work in progress with Georges Skandalis.

URL: Event link

Mathematical Physics and Harmonic Analysis Seminar

Time: 2:00PM - 2:50PM

Location: Zoom

Speaker: Rostislav Grigorchuk, Texas A&M University

Title: Spectra of groups and graphs: a short survey.

Abstract: In my talk I will touch on such topics as the shape of the spectrum of Cayley and Schreier graphs of finitely generated groups, type of spectral measures, the question of A.Valette "Can one hear the shape of a group", and the relation to the random Schodinger operator.

Based on numerous results with coauthors: L.Bartholdi, A.Zuk, Z.Sunic, D.Lenz, T.Nagnibeda, A.Perez, B.Simanek, A.Dudko and others.

Algebra and Combinatorics Seminar

Time: 3:00PM - 4:00PM

Location: Zoom

Speaker: Chun-Hung Liu, TAMU

Title: Well-quasi-ordering digraphs by the strong immersion relation

Abstract: A well-quasi-ordering is a reflexive and transitive binary relation such that every infinite sequence has a non-trivial increasing subsequence. The study of well-quasi-ordering was stimulated by two conjectures of Vazsonyi in 1940s: trees and subcubic graphs are well-quasi-ordered by the topological minor relation. It is known that the topological minor relation does not well-quasi-order all graphs. Nash-Williams in 1960s introduced the notion of strong immersion and conjectured that the strong immersion relation well-quasi-orders all graphs, which is a common generalization of both conjectures of Vazsonyi. In this talk we consider strong immersion on digraphs. Paths that change direction arbitrarily many times form an infinite antichain with respect to the strong immersion relation. In this talk, we will prove that it is the only obstruction. Namely, for any integer k, digraphs with no paths that change direction at least k times are well-quasi-ordered by the strong immersion relation. Joint work with Irene Muzi.