Colloquium

  • 2019 Nov 07

    Colloquium: Boaz Klartag (Weizmann) - Needle decomposition and Ricci curvature

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    Title: Needle decomposition and Ricci curvature
    Abstract: Needle decomposition is a technique in convex geometry,
    which enables one to prove isoperimetric and spectral gap
    inequalities, by reducing an n-dimensional problem to a 1-dimensional
    one. This technique was promoted by Payne-Weinberger, Gromov-Milman
    and Kannan-Lovasz-Simonovits. In this lecture we will explain what
    needles are, what they are good for, and why the technique works under
    lower bounds on the Ricci curvature.
  • 2019 Oct 31

    Colloquium: Leonid Polterovich (TAU) - Quantum footprints of symplectic rigidity

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    Title: Quantum footprints of symplectic rigidity
    Abstract: I'll discuss an interaction between symplectic topology, a rapidly developing mathematical area originated as a geometric language for problems of classical mechanics, and quantum mechanics. On one hand, ideas from quantum mechanics give rise to new structures on the symplectic side, and quantum mechanical insights lead to useful symplectic predictions. On the other hand, some phenomena discovered within symplectic topology admit a translation into the language of quantum mechanics.
  • 2019 Jun 27

    Colloquium Dvoretzky lecture: Assaf Naor(Princeton) - An average John theorem

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem

    Abstract: We will prove a sharp average-case variant of a classical embedding theorem of John through the theory of nonlinear spectral gaps. We will use this theorem to provide a new answer to questions of Johnson and Lindenstrauss (1983) and Bourgain (1985) on metric dimension reduction, and explain how it leads to algorithms for approximate nearest neighbor search.
  • 2019 Jun 06

    Colloquium: Ram Band (Technion) - Neumann Domains

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    Abstract:
    The nodal set of a Laplacian eigenfunction forms a partition of the underlying manifold.
    An alternative partition, based on the gradient field of the eigenfunction, is via the so called Neumann domains.
    A Neumann domain of an eigenfunction is a connected component of the intersection between the stable
    manifold of a certain minimum and the unstable manifold of a certain maximum.
    We introduce this subject, discuss various properties of Neumann domains and
    point out the similarities and differences between nodal domains and Neumann domains.
  • 2019 May 30

    Colloquium: Alon Nishry (TAU) - Zeros of random power series

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem

    Abstract:
    A central problem in complex analysis is how to describe zero sets of power series in terms of their coefficients. In general, it is difficult to obtain precise results for a given function. However, when the function is defined by a power series, whose coefficients are independent random variables, such results can be obtained. Moreover, if the coefficients are complex Gaussians, the results are especially elegant. In particular, in this talk I will discuss some different notions of "rigidity" of the zero sets.
  • 2019 May 23

    Colloquium: Yves Benoist (University of Paris-Sud) - Arithmeticity of discrete groups

    2:30pm to 3:30pm

    Location: 

    Manchester Building (Hall 2), Hebrew University Jerusalem
    By a theorem of Borel and Harish-Chandra,
    an arithmetic group in a semisimple Lie group is a lattice.
    Conversely, by a celebrated theorem of Margulis,
    in a higher rank semisimple Lie group G
    any irreducible lattice is an arithmetic group.
    The aim of this lecture is to survey an
    arithmeticity criterium for discrete subgroups
    which are not assumed to be lattices.
    This criterium, obtained with Miquel,
    generalizes works of Selberg and Hee Oh
    and solves a conjecture of Margulis. It says:

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