Princeton University

Fri 26 Feb 2016, 3:00pm
SPECIAL
Department Colloquium / PIMS Seminars and PDF Colloquiums
ESB 2012

Coloring some perfect graphs PIMS/UBC Distinguished Colloquium

ESB 2012
Fri 26 Feb 2016, 3:00pm4:00pm
Abstract
Perfect graphs are a class of graphs that behave particularly well with respect to coloring. In the 1960's Claude Berge made two conjectures about this class of graphs, that motivated a great deal of
research, and by now they have both been solved.
The following remained open however: design a combinatorial algorithm that produces an optimal coloring of a perfect graph. Recently, we were able to make progress on this question, and we will discuss it in this talk. Last year, in joint work with Lo, Maffray, Trotignon and Vuskovic we were able to construct such an algorithm under the additional assumption that the input graph is squarefree (contains no induced fourcycle). More recently, together with Lagoutte, Seymour and Spirkl, we solved another case of the problem, when the clique number of the input graph is fixed (and not part of the input).
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UC Berkeley

Fri 4 Mar 2016, 3:00pm
SPECIAL
Department Colloquium
ESB 2012

PIMS Hugh Morris Lecture

ESB 2012
Fri 4 Mar 2016, 3:00pm4:00pm
Abstract
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University of Toronto

Fri 11 Mar 2016, 3:00pm
Department Colloquium
Math Annex 1100

Monodromy of shift of argument eigenvectors and cactus groups

Math Annex 1100
Fri 11 Mar 2016, 3:00pm4:00pm
Abstract
The classical method of GelfandZetlin constructs bases in representations of gl_n using iterative restriction to smaller gl_k. For any semisimple Lie algebra this can be generalized using eigenvectors for maximal commutative subalgebra of universal envelopping algebras. In this way, we obtain a family of bases for representations of our Lie algebra. This family is parametrized by the moduli space of marked genus 0 real curves. The fundamental group of this moduli space is called the cactus group and thus we obtain an an action of the cactus group on one of these bases. This action of the cactus group matches an action defined combinatoriallyusing crystals.
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Harvard University

Fri 18 Mar 2016, 3:00pm
SPECIAL
Department Colloquium / PIMS Seminars and PDF Colloquiums
ESB2012

PIMSUBC Distinguished ColloquiumThe Siegel Mass Formula, Tamagawa Numbers, and Nonabelian Poincare Duality

ESB2012
Fri 18 Mar 2016, 3:00pm4:00pm
Abstract
Let L be a positive definite lattice. There are only finitely many positive definite lattices L' which are isomorphic to L modulo N for every N > 0: in fact, there is a formula for the number of such lattices, called the Siegel mass formula. In this talk, I'll review the Siegel mass formula and explain how it was reformulated by Weil as a statement about volumes of adelic groups. I'll then describe some joint work with Dennis Gaitsgory on computing these volumes over function fields using ideas from topology: in particular, a nonabelian version of Poincare duality.
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Courant Institute, NYU

Fri 1 Apr 2016, 3:00pm
SPECIAL
Department Colloquium
ESB2012

PIMSUBC Distinguished ColloquiumTBA

ESB2012
Fri 1 Apr 2016, 3:00pm4:00pm
Abstract
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Fri 9 Sep 2016, 3:00pm
SPECIAL
Department Colloquium
ESB 2012

PIMSUBC Distinguished ColloquiumTBA

ESB 2012
Fri 9 Sep 2016, 3:00pm4:00pm
Abstract
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University of Minnesota

Fri 23 Sep 2016, 3:00pm
SPECIAL
Department Colloquium
ESB 2012

PIMSUBC Distinguished ColloquiumTBA

ESB 2012
Fri 23 Sep 2016, 3:00pm4:00pm
Abstract
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