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Advances in Representation Theory of Algebras IX (ARTA)

June 12th-16th, 2023

Dynamics, Geometry and Groups Seminar

Wednesday, May 10th, 2023

Time: 3:30 p.m.  Place: Jeffery Hall, Room 422

Speaker: Rémi Coulon (Université de Rennes)

Title: Growth problems in negatively curved groups

Abstract: Given a group G acting by isometries on a metric space X, its exponential growth rate provides a way to measure the "size" of its orbits. More precisely it quantifies te asymptotic behavior of the number of orbit points in a ball. When G is the fundamental group of a compact hyperbolic manifold M acting on the universal cover X of M, then this rate has numerous interpretations both of geometric and dynamical nature. In particular it is the entropy of the geodesic flow on the unit tangent bundle of M. In this configuration the study of the geodesic flow on M (and its covers) provides useful informations on the growth rates of G and its subgroups.

In this talk we will present a work in progress whose aim is to exploit similar techniques, while strongly relaxing the hypothesis on the curvature of X. For our purpose, it suffices to assume that the group G contains a "contracting element', which can be thought of as a "hyperbolic direction". Besides fundamental groups of hyperbolic manifolds, this general framework encompasses (relatively) hyperbolic groups, modular groups of surfaces, many right angled Artin groups, etc. As an application we will provide an amenability criterion for the quotients of G.

Algebra & Geometry Seminar

Tuesday, April 17th, 2023

Time: 4:30 p.m.  Place: Jeffery Hall, Room 222

Speaker: Lucas Gagnon (York University)

Title: Quasisymmetric varieties, excedance classes, and bases for the Temperley–Lieb algebra

Abstract:

Website details here: https://mast.queensu.ca/~georep/Fall%20'22.html

Math Club

Thursday, April 6th, 2023

Time: 5:30 p.m.  Place: Jeffery Hall, Room 118

Speaker: David Wehlau (RMC & ºÚÁϳԹÏ×ÊÔ´)

Title: Proofs from the Book

Abstract: The Hungarian Mathematician Paul Erdös (1913-1996) was one of the top mathematicians of the past century. He published more mathematical articles during his lifetime than anyone else in history. He did this by being utterly consumed by mathematics to the exclusion of all else.

Erdös believed that every mathematical result had one best, most elegant proof and that such proofs were recorded in one volume, known to Erdös as ``The Book''. I will describe some of Erdös' life and explain a few proofs that may be in The Book. I will start with the question: If $a$ and $b$ are irrational can $a^b$ be rational? There is an answer to this question that I believe belongs in The Book.

Probability Seminar

Wednesday, April 5th, 2023

Time: 12:00 p.m.  Place: Jeffery Hall, Room 319

Speaker: Alex Dunlap (NYU)

Title: The nonlinear stochastic heat equation in the critical dimension

Abstract: I will discuss a two-dimensional stochastic heat equation with a nonlinear noise strength, and consider a limit in which the correlation length of the noise is taken to 0 but the noise is attenuated by a logarithmic factor. The limiting pointwise statistics can be related to a stochastic differential equation in which the diffusivity solves a PDE somewhat reminiscent of the porous medium equation. This relationship is established through the theory of forward-backward SDEs. I will also explain several cases in which the PDE can be solved explicitly, some of which correspond to known probabilistic models. This talk will be based on current joint work with Cole Graham and earlier joint work with Yu Gu.

Algebra & Geometry Seminar

Tuesday, April 11th, 2023

Time: 1:00 p.m.  Place: Jeffery Hall, Room 222

Speaker: Rita Fioresi (University of Bologna)

Title: On generalized root systems

Abstract:

Website details here: https://mast.queensu.ca/~georep/Fall%20'22.html

Math Club

Thursday, March 30th, 2023

Time: 5:30 p.m.  Place: Jeffery Hall, Room 118

Speaker: Greg Smith (Queen's University)

Title: How to win a Field’s Medal?

Abstract: Why was June Huh awarded a Fields Medal in 2022?

In this talk, we will probe some connections between combinatorics and algebraic geometry. We hope to provide an understanding of the Dowling-Wilson conjecture and some insight into its proof.

Curves Seminar

Wednesday, March 29th, 2023

Time: 1:00 p.m.  Place: Jeffery Hall, Room 222 & Zoom

Speaker: Sonja Ruzic

Title: Orbit-Cone Correspondence

Abstract: For a toric variety V with torus T, we will look at an example to see how the normal fan of V is related to the T-orbits in V. Then we will formalize these ideas via the Orbit-Cone Correspondence theorem.

Algebra & Geometry Seminar

Monday, April 3rd, 2023

Time: 4:30 p.m.  Place: Jeffery Hall, Room 222

Speaker: Greg Smith (ºÚÁϳԹÏ×ÊÔ´)

Title: Cohomology of toric vector bundles

Abstract:

Website details here: https://mast.queensu.ca/~georep/Fall%20'22.html

Math & Stats Department Colloquium

Friday, March 31st, 2023

Time: 2:30 p.m.  Place: Jeffery Hall, Room 234

Speaker: Hanna Jankowski (York University)

Title: Some results for the Isotonic Single Index model

Abstract: The semiparametric single index model is a popular dimension reduction tool used in a variety of applications. It can be viewed as a further generalization of generalized linear models, where the link function is not specified. In this talk, I will discuss the isotonic version of the nonparametric single index model, where the link function is assumed to be increasing. A key benefit of the assumption is that this approach is free of any additional tuning parameters, such as the bandwidth. Furthermore, nearly all parametric generalized index models have increasing link functions, making it a very natural assumption. In this talk, I will discuss estimation, computation, as well as rates of convergence under different underlying assumptions for the isotonic index model. This is joint work with Fadoua Balabdaoui from ETH Zurich and Cecile Durot from Paris X Nanterre.