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# Events for 11/18/2020 from all calendars

## Colloquium - Lei Chen

## Probability Seminar

## Topology Seminar

## Student/Postdoc Working Geometry Seminar

**Time: ** 1:00PM - 2:00PM

**Location: ** Zoom

**Speaker: **Lei Chen, Caltech

**Description: ****Title:** Actions of Homeo and Diffeo groups on manifolds
**Abstract:** In this talk, I discuss the general question of how to
obstruct and construct group actions on manifolds. I will focus on large
groups like Homeo(M) and Diff(M) about how they can act on another
manifold N. The main result is an orbit classification theorem, which
fully classifies possible orbits. I will also talk about some low
dimensional applications and open questions. This is a joint work with
Kathryn Mann.

**Time: ** 2:00PM - 3:00PM

**Location: ** Zoom

**Speaker: **Jens Malmquist, University of British Columbia (UBC)

**Title: ***Stability of heat kernel estimates and parabolic Harnack inequality for symmetric jump processes on metric measure spaces with atoms*

**Abstract: **Consider a (continuous-time) symmetric Markovian jump process on a metric measure space. If the underlying metric measure space satisfies the volume-doubling and reverse-volume-doubling properties, then it is known that two-sided heat kernel estimates and the parabolic Harnack inequality are both stable under bounded perturbations of the jumping measure. However, the reverse-volume-doubling condition fails if the metric measure space is a graph (or more generally, if it contains any atoms). We generalize these previously known stability results to spaces that satisfy what may be thought of as "reverse-volume-doubling at sufficiently large scales". In particular, we show that heat kernel estimates and the parabolic Harnack inequality are both stable for symmetric jump processes on graphs (with the usual graph metric) that have infinite diameter and satisfy the volume-doubling property.

**Time: ** 4:00PM - 5:00PM

**Location: ** Zoom

**Speaker: **Honghao Gao, Michigan State University

**Title: ***Legendrian invariants, Lagrangian fillings and cluster algebras*

**Abstract: **Classifications of Legendrian knots and their exact Lagrangian fillings are central questions in low-dimensional contact and symplectic topology. Recent development suggests that one can use cluster seeds to distinguish exact Lagrangian fillings. It requires a filling-to-cluster functoriality over a moduli space of Legendrian invariants. This invariant can be sheaf theoretic (Shende-Treumann-Williams-Zaslow) or Floer theoretic (joint work with Linhui Shen and Daping Weng). As an application, I will explain how to use Legendrian loops and cluster algebras to construct infinitely many exact Lagrangian fillings for most torus links (joint work with Roger Casals, using sheaf-theoretic invariants), and for most positive braid links (joint work with Linhui Shen and Daping Weng, using Floer-theoretic invariants).

**Time: ** 11:00PM - 12:00PM

**Location: ** zoom

**Speaker: **JM Landsberg, TAMU

**Title: ***The substitution method and linear sections of spaces of matrices of bounded rank*