Abstracts

Week of October 31, 2021

November 1, 2021
Group Actions and Dynamics Recurrence criterion for walks on infinite volume homogeneous spaces. 10:15am -
Zoom

A famous theorem due to Hopf-Tsuji-Sullivan-Kaimanovich asserts that the geodesic flow and the Brownian motion on a rank-one symmetric space of the non-compact type $\Lambda \backslash G/K$ are either both recurrent ergodic or both transient. In this talk, I will explain how this dichotomy can be extended to a much larger class of random walks, namely any right random walk on $\Lambda \backslash G$ induced by a Zariski-dense probability measure on $G$ with finite first moment.

Geometry, Symmetry and Physics Co-t-structures in geometric representation theory 4:30pm -
Zoom

Abstract: The notion of a "t-structure on a triangulated category" was introduced around 1980. The notion of "co-t-structure" could have been defined back then as well, but it didn't receive much attention until the past 10 years or so, probably because it wasn't clear what it was good for. I'll explain these notions and give some elementary examples. I will then discuss some "modern" examples of co-t-structures in geometric representation theory. In particular, I will explain a remarkable new co-t-structure on the derived category of coherent sheaves on the nilpotent cone of a reductive group. The study of this co-t-structure leads to the proof of the Humphreys conjecture on tilting modules for a reductive group. This is joint work with W. Hardesty.

Zoom link: https://yale.zoom.us/j/99305994163, contact the organizers (Gurbir Dhillon and Junliang Shen) for the passcode.

November 2, 2021
Geometry & Topology Uniform models part 2 4:15pm -
LOM 214

Following up on last week's talk, I will sketch a little more about the structure and properties of uniform models for surface groups and for the general incompressible-boundary case. I will then explain how this allows us to prove Thurston's "lost" theorem: a certain self-map of Teichmuller space, used in the solution to the gluing problem, has an iterate with bounded image.

Algebra and Number Theory Seminar Geometry of local Arthur packets for simple unramified Arthur parameters for $\mathrm{GL}_n$ 4:30pm -
Zoom

The local Langlands correspondence for a connected reductive $p$-adic group $G$ partitions the set of equivalence classes of smooth irreducible representations of $G(F)$ into $L$-packets using equivalence classes of Langlands parameters. Vogan's geometric perspective gives us a moduli space of Langlands parameters, and the correspondence can be viewed as a relation between the set of equivalence classes of smooth irreducible representations of $G(F)$ and simple objects in the category of equivariant perverse sheaves on the moduli space of Langlands parameters that share a common infinitesimal parameter. This geometry gives us the notion of an ABV-packet, a set of smooth irreducible representations of $G(F)$, which conjecturally generalizes the notion of a local Arthur packet - a local Arthur packet is conjecturally an ABV-packet. In this talk, we will look at Langlands parameters coming from simple Arthur parameters in the case of $\mathrm{GL}_n.$ We will explore the geometry of the moduli space of Langlands parameters using an example. We will see work in progress towards proving that the local Arthur packet is the ABV-packet for this case.

November 3, 2021
Applied Mathematics How to apply manifold learning and random matrix theory to study complicated time series? 2:30pm -
https://yale.zoom.us/j/2188028533

Abstract: Compared with the snapshot health record information, long-term and high-frequency physiological time series provide health information from the other dimension, which is particularly important in the post-COVID era. I will discuss recent progress in dealing with this kind of time series by manifold learning and random matrix theory. Associated theoretical support toward statistical inference will be discussed. Its clinical application in the electroencephalogram (EEG), and local field potential (LFP) if time permits, will be demonstrated.

Undergraduate Seminar Putnam Seminar 4:00pm -
LOM 214
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LOM 214
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LOM 214
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LOM 214
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LOM 214
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LOM 214
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LOM 214
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LOM 214
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LOM 214
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LOM 214
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LOM 214

The Putnam seminar meets every Wednesday from 4 to 5:30 in LOM 214.  As always, everyone is warmly welcomed to come to hang out, learn more cool math, and meet folks.  The seminar is casual, and folks can come and go as they like.  See Pat Devlin’s webpage (and/or contact him) for more information.  Folks can sign up for the mailing list here: https://forms.gle/nYPx72KVJxJcgLha8

November 4, 2021
Algebra and Geometry lecture series Quantizations in charateristic p. Lecture 8 4:00pm -
https://yale.zoom.us/j/99019019033 (password was emailed by Ivan)

This is the 8th lecture in the series. See Algebra and Geometry lecture series (yale.edu) for details.

Analysis Asymptotic stability for the sine-Gordon kink under odd perturbations via super-symmetry 4:15pm -

Abstract:

We will describe the recent asymptotic analysis with Jonas Luehrmann (TAMU) of the Sine-Gordon evolution of odd data near the kink. We do

not rely on the complete integrability of the problem in a direct way, in particular we do not use the inverse scattering transform.

November 5, 2021
Geometric Analysis and Application Singular behavior of min-max minimal hypersurfaces in dimension 8 2:00pm -

Abstract:

In this talk I will discuss an estimate on the index and number of “non-minimizing” singular points for one parameter min-max minimal hypersurfaces in 8-dimensional compact manifolds. As a consequence I will discuss the generic existence of smooth embedded minimal hypersurfaces in 8-dimensional compact manifolds. This joint work with Otis Chodosh (Stanford) and Yevgeny Liokumovich (University of Toronto).