Tag - Lattices

Dalimil Mazac: Sphere Packings, Spectral Gaps and the Conformal Bootstrap

8th November, 2023

I will discuss infinite-dimensional linear programs producing bounds on the spectral gap in various settings. This includes new bounds on the spectral gap of hyperbolic manifolds as well as the Cohn-Elkies bound on the density of sphere packings. The bounds allow us to essentially determine the complete set of spectral gaps achieved by hyperbolic 2-orbifolds. The linear programs involved have been the subject of intense study by mathematical physicists in the context of the conformal bootstrap.

I will review the method of analytic extremal functionals, introduced by the speaker to prove sharp bounds in the conformal bootstrap. When used within the Cohn-Elkies linear program, this method reproduces the groundbreaking solution of Viazovska et al of the sphere packing problem in dimensions 8 and 24, as well as the interpolation basis used in the proof of universal optimality of the E8 and Leech lattice. The connections covered in this talk offer a broader framework for studying optimality in infinite-dimensional linear programs.

Mikhail Belolipetsky: Growth of lattices in semisimple Lie groups

22nd April, 2021

A discrete subgroup G of a Lie group H is called a lattice if the quotient space G/H has finite volume. By a classical theorem of Bieberbach we know that the group of isometries of an n-dimensional Euclidean space has only finitely many different types of lattices. The situation is different for the semisimple Lie groups H. Here the total number of lattices is infinite and we can study its growth rate with respect to the covolume. This topic has been a subject of our joint work with A. Lubotzky for a number of years. In the talk I will discuss our work and some other more recent related results.

Federico Rodriguez Hertz: Rigidity of hyperbolic higher rank lattice actions

3rd December, 2013

I will discuss some recent results with Aaron Brown and Zhiren Wang on actions by higher rank lattices on nilmanifolds. I will present the result in the simplest case possible, SL(n,ℤ) acting on 𝕋n, and try to present the ideas of the proof. The result imply existence of invariant measures for SL(n,ℤ) actions on 𝕋n with standard homotopy data as well as global rigidity of Anosov actions on infranilmanifolds and existence of semiconjugacies without assumption on existence of invariant measure.