Mon, 06 Jun 2022

15:30 - 16:30
L5

Ribbon concordance is a partial order on knots

Ian Agol
(Berkeley)
Abstract

We show that ribbon concordance forms a partial ordering on the set of knots, answering a question of Gordon. The proof makes use of representation varieties of the knot groups to S O(N) and relations between them induced by a ribbon concordance.

Thu, 02 May 2019

13:00 - 14:00
L4

A class of stochastic games and moving free boundary problems

Renyuan Xu
(Berkeley)
Abstract

Stochastic control problems are closely related to free boundary problems, where both the underlying fully nonlinear PDEs and the boundaries separating the action and waiting regions are integral parts of the problems. In this talk, we will propose a class of stochastic N-player games and show how the free boundary problems involve moving boundaries due to the additional game nature. We will provide explicit Nash equilibria by solving a sequence of Skorokhod problems. For the special cases of resource allocation problems, we will show how players change their strategies based on different network structures between players and resources. We will also talk about the insights from a sharing economy perspective. This talk is based on a joint work with Xin Guo (UC Berkeley) and Wenpin Tang (UCLA).

Tue, 08 May 2018

16:00 - 17:00
L5

Variants of Mordell-Lang

Thomas Scanlon
(Berkeley)
Abstract


I will report on two recent papers with D. Ghioca and U. Zannier (joined by P. Corvaja and F. Hu, respectively) in which we consider variants of the Mordell-Lang conjecture.  In the first of these, we study the dynamical Mordell-Lang conjecture in positive characteristic, proving some instances, but also showing that in general the problem is at least as hard as a difficult diophantine problem over the integers.  In the second paper, we study the Mordell-Lang problem for extensions of abelian varieties by the additive group.  Here we have positive results in the function field case obtained by using the socle theorem in the form offered as an aside in Hrushovski's 1996 paper and in the number field case we relate this problem to the Bombieri-Lang conjecture.

Tue, 20 Feb 2018

16:00 - 17:00
L1

Linear orders in NIP theories

Pierre Simon
(Berkeley)
Abstract

A longstanding open question asks whether every unstable NIP theory interprets an infinite linear order. I will present a construction that almost provides a positive answer. I will also discuss some conjectural applications to the classification of omega-categorical NIP structure, generalizing what is known for omega-stable, and classification of models mimicking the superstable case.
 

Tue, 10 Oct 2017

15:45 - 16:45
L4

Mirror symmetry for affine hypersurfaces

Benjamin Gammage
(Berkeley)
Abstract

Using tropical geometry and new methods in the theory of Fukaya categories, we explain a mirror symmetry equivalence relating the Fukaya category of a hypersurface and the category of coherent sheaves on the boundary of a toric variety.

Thu, 30 Jun 2011
17:00
L3

tba

Thomas Scanlon
(Berkeley)
Mon, 20 Jun 2011

15:45 - 16:45
L3

The classification of subfactors of small index and the onset of wilderness

Voughan Jones
(Berkeley)
Abstract
In the 1990's Haagerup discovered a new subfactor, and hence a new topological quantum field theory, that has so far proved inaccessible by the methods of quantum groups and conformal field theory. It was the subfactor of smallest index beyond 4. This led to a classification project-classify all subfactors to as large an index as possible. So far we have gone as far as index 5. It is known that at index 6 wildness phenomena occur which preclude a simple listing of all subfactors of that index. It is possible that wildness occurs at a smaller index value, the main candidate being approximately 5.236.
Thu, 18 Jun 2009
11:00

The virtual fibering conjecture and related questions

Ian Agol
(Berkeley)
Abstract

Thurston asked a bold question of whether finite volume hyperbolic 3-manifolds might always admit a finite-sheeted cover which fibers over the circle. This talk will review some of the progress on this question, and discuss its relation to other questions including residual finiteness and subgroup separability, the behavior of Heegaard genus in finite-sheeted covers, CAT(0) cubings, the RFRS condition, and subgroups of right-angled Artin groups. In particular, hyperbolic 3-manifolds with LERF fundamental group are virtually fibered. Some applications of the techniques will also be mentioned.

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