Events & Seminars

2017 Nov 30

Colloquium: Doron Puder (Tel Aviv) - "Matrix Integrals, Graphs on Surfaces and Mapping Class Group"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Since the 1970's, Physicists and Mathematicians who study random matrices in the standard models of GUE or GOE, are aware of intriguing connections between integrals of such random matrices and enumeration of graphs on surfaces. We establish a new aspect of this theory: for random matrices sampled from the group U(n) of Unitary matrices. The group structure of these matrices allows us to go further and find surprising algebraic quantities hidden in the values of these integrals. The talk will be aimed at graduate students, and all notions will be explained.
2017 Dec 14

Colloquium: Yoel Groman (Columbia) - "Mirror symmetry for toric Calabi Yau 3-folds"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
Mirror symmetry is a far reaching duality relating symplectic geometry on a given manifold to complex geometry on a completely different manifold - its mirror. Toric Calabi Yau manifolds are a large family of examples which which have served as a testing ground for numerous ideas in the study of mirror symmetry. I will prove homological mirror symmetry when the symplectic side is a toric Calabi-Yau 3-fold. I will aim to explain geometrically why the mirror of a toric Calabi Yau takes the particular form it does.
2017 Nov 02

Colloquium: Michael Brandenbursky (BGU) "Entropy, metrics and quasi-morphisms."

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
One of the mainstream and modern tools in the study of non abelian groups are quasi-morphisms. These are functions from a group to the reals which satisfy homomorphism condition up to a bounded error. Nowadays they are used in many fields of mathematics. For instance, they are related to bounded cohomology, stable commutator length, metrics on diffeomorphism groups, displacement of sets in symplectic topology, dynamics, knot theory, orderability, and the study of mapping class groups and of concordance group of knots.
2017 Nov 04

Colloquium: Michael Brandenbursky (BGU) - "Entropy, metrics and quasi-morphisms"

2:30pm to 3:30pm

Location: 

Manchester Building (Hall 2), Hebrew University Jerusalem
One of the mainstream and modern tools in the study of non abelian groups are quasi-morphisms. These are functions from a group to the reals which satisfy homomorphism condition up to a bounded error. Nowadays they are used in many fields of mathematics. For instance, they are related to bounded cohomology, stable commutator length, metrics on diffeomorphism groups, displacement of sets in symplectic topology, dynamics, knot theory, orderability, and the study of mapping class groups and of concordance group of knots.
2017 Dec 18

SPECIAL Jerusalem Analysis and PDEs seminar: "Steady Water Waves" Walter Strauss (Brown University)

4:00pm to 5:00pm

Location: 

Ross 63
I will consider classical 2D traveling water waves with vorticity. By means of local and global bifurcation theory using topological degree, we can prove that there exist many such waves. They are exact smooth solutions of the Euler equations with the physical boundary conditions. Some of the waves are quite tall and steep and some are overhanging. There are periodic ones and solitary ones. I will exhibit some numerical computations of such waves. New analytical results will be presented on waves with favorable vorticity.
2015 Oct 22

Colloquium: Nir Avni (Northwestern), "Counting points and counting representations"

2:30pm to 3:30pm

Title: Counting points and counting representations Abstract: I will talk about the following questions: 1) Given a system of polynomial equations with integer coefficients, how many solutions does it have in the ring Z/N? 2)​ Given a polynomial map f:R^a-->R^b and a smooth, compactly supported measure m on R^a, does the push-forward of m by f have bounded density? 3) Given a lattice in a higher rank Lie group (say, SL(n,Z) for n>2). How many d-dimensional representations does it ​have?
2017 Jan 22

Special colloquium: Laci Babai (Chicago) "Graph isomorphism and coherent configurations: The Split-or-Johnson routine"

4:00pm to 6:00pm

Location: 

Rothberg B220 (CS bldg)
Coherent configurations" (CCs) are certain highly regular colorings of the directed complete graph. The concept goes back to Schur (1933) who used it to study permutation groups, and has subsequently been rediscovered in other contexts (block designs, association schemes, graph canonization). CCs are the central concept in the "Split-or-Johnson" (SoJ) procedure, one of the main combinatorial components of the speaker's recent algorithm to test graph isomorphism.

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