Colloquium

  • 2015 Dec 03

    Colloquium: Ofer Zeitouni (Weizmann), "Extremes of logarithmically correlated fields"

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    Title: Extremes of logarithmically correlated fields
    Abstract: The general theory of Gaussian processes gives a recipe for estimating the maximum of a random field,
    which is neither easy to compute nor sharp enough for obtaining the law of the maximum. In recent years, much effort was invested in understanding the extrema of logarithmically correlated fields, both Gaussian and non-Gaussian. I will explain the motivation, and discuss some of the recent results and the techniques that have been involved in proving them.
  • 2015 Nov 26

    Colloquium: Shai Evra (HUJI), "Topological Expanders"

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    Title: Topological Expanders.
    Abstract:
    A classical result of Boros-Furedi (for d=2) and Barany (for d>=2) from the 80's, asserts that given any n points in R^d, there exists a point in R^d which is covered by a constant fraction (independent of n) of all the geometric (=affine) d-simplices defined by the n points. In 2010, Gromov strengthen this result, by allowing to take topological d-simplices as well, i.e. drawing continuous lines between the n points, rather then straight lines and similarly continuous simplices rather than affine.
  • 2015 Nov 19

    Colloquium: Shmuel Weinberger (Chicago), "The Quantitative challenge to topology"

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    Serre's thesis and its aftermath rolled in a golden age of algebraic topology which led to the impression that we can really understand (necessarily highly nonlinear) maps from one space to another. With the work of Thom on cobordism and Smale on immersions and the Poincare conjecture, a paradigm developed where geometric problems would be solved by reduction to algebraic topological ones.
  • 2015 Nov 12

    Colloquium: Michael Krivelevich (Tel Aviv), "Positional games"

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    Title: Positional games
    Positional games are a branch of combinatorics, researching a variety of two-player games, ranging from popular recreational games such as Tic-Tac-Toe and Hex, to purely abstract games played on graphs and hypergraphs. It is closely connected to many other combinatorial disciplines such as Ramsey theory, extremal graph and set theory, probabilistic combinatorics, and to computer science.
  • 2015 Oct 29

    Colloquium: Vincent Guirardel (Universite de Renne 1), "Avatars of small cancellation"

    2:30pm to 3:30pm

    Title: Avatars of small cancellation
    Abstract:
    In general, given a finite presentation of a group, it is very difficult (in fact algorithmically impossible) to understand the group it defines. Small cancellation theory was developped as a combinatorial condition on a presentation that allows one to understand the group it represents. This very flexible construction has many applications to construct examples of groups with specific features.
  • 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?

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