Colloquium

  • 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 Dec 07

    Colloquium: Nikita Rozenblyum (Chicago) - "String topology and noncommutative geometry"

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    A classical result of Goldman states that character variety of an oriented surface is a
    symplectic algebraic variety, and that the Goldman Lie algebra of free loops on the surface
    acts by Hamiltonian vector fields on the character variety. I will describe a vast
    generalization of these results, including to higher dimensional manifolds where the role of
    the Goldman Lie algebra is played by the Chas-Sullivan string bracket in the string topology
    of the manifold. These results follow from a general statement in noncommutative geometry.
  • 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 Nov 23

    Colloquium: Andreas Thom (Dresden) - "Topological methods to solve equations over groups"

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    I will survey various approximation properties of finitely generated groups and explain how they can be used to prove various longstanding conjectures in the theory of groups and group rings. A large class of groups (no group known to be not in the class) is presented that satisfy the Kervaire-Laudenbach Conjecture about solvability of non-singular equations over groups. Our method is inspired by seminal work of Gerstenhaber-Rothaus, which was the key to prove the Kervaire-Laudenbach Conjecture for residually finite groups.
  • 2017 Nov 16

    Colloquium: John R. Klein (Wayne State U.) - "Algebraic Topology and Fluctuations"

    2:40pm to 3:40pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    This talk will investigate a certain class of continuous time Markov processes using machinery from algebraic topology. To each such process, we will associate a homological observable, the average current, which is a measurement of the net flow of probability of the system. We show that the average current quantizes in the low temperature limit. We also explain how the quantized version admits a topological description.
  • 2017 Nov 09

    Colloquium: Nir Lev (Bar Ilan University) - Fourier quasicrystals

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    By a Fourier quasicrystal we mean a pure point measure in R^d,
    whose Fourier transform is also a pure point measure. This notion
    was inspired by the experimental discovery of quasicrystalline
    materials in the middle of 80's.
    The classical example of such a measure comes from Poisson's
    summation formula. Which other measures of this type may exist?
    I will give the relevant background on this problem and present
    our recent results obtained in joint work with Alexander Olevskii.
  • 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 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 Sep 14

    Colloquium: Kate Juschenko (Northwestern University) - "Cycling amenable groups and soficity"

    2:30pm to 3:30pm

    Location: 

    IIAS hall, Hebrew University Jerusalem
    I will give introduction to sofic groups and discuss a possible strategy towards finding a non-sofic group. I will show that if the Higman group were sofic, there would be a map from Z/pZ to itself, locally like an exponential map, satisfying a rather strong recurrence property. The approach to (non)-soficity is based on the study of sofic representations of amenable subgroups of a sofic group. This is joint work with Harald Helfgott.

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