Arithmetic theta series

Stephan Kudla
University of Toronto
March 8, 2018
Abstract: In recent joint work with Jan Bruinier, Ben Howard, Michael Rapoport and Tonghai Yang,
we proved that a certain generating series for the classes of arithmetic divisors on a regular integral model M of a Shimura variety
for a unitary group of signature (n-1,1) for an imaginary quadratic field is a modular form of weight n valued in the
first arithmetic Chow group of M. I will discuss how this is proved, highlighting the main steps.
Key ingredients include information about the divisors of Borcherds forms on the integral model

Euler classes transgressions and Eistenstein cohomology of GL(N)

Nicolas Bergeron
IMJ PRG
March 8, 2018
Abstract: In work-in-progress with Pierre Charollois, Luis Garcia and Akshay Venkatesh we give a new construction of some Eisenstein classes for $GL_N (Z)$ that were first considered by Nori and Sczech. The starting point of this construction is a theorem of Sullivan on the vanishing of the Euler class of $SL_N$ (Z)-vector bundles and the explicit transgression of this Euler class by Bismut and Cheeger. Their proof indeed produces a universal form that can be thought of as a kernel for a regularized theta lift for the reductive dual pair $(GL_1 , GL_N )$.

The Plancherel formula for L^2(GL_n(F)\GL_n(E)) and applications to the Ichino-Ikeda and formal degree conjectures for unitary groups

Raphael Beuzart-Plessis
CNRS
March 6, 2018
Abstract : Let $E/F$ be a quadratic extension of local fields of characteristic zero. In this talk, I will explain two ways to compute the Plancherel decomposition of $L^2(GL_n(F)\backslash GL_n(E))$. In both cases, the result involves the image of base change from unitary groups to $GL_n(E)$ and is in accordance with a general conjecture of Sakellaridis-Venkatesh on the spectral decomposition of spherical varieties. We will also give applications of our formulas to the so-called Ichino-Ikeda and formal degree conjectures for unitary groups.

Restriction problem for non-generic representation of Arthur type

Wee Teck Gan
National University of Singapore
March 6, 2018
Abstract: The Gross-Prasad conjecture considers a branching problem for generic Arthur packets of classical groups. In this talk, we will describe progress towards extending this conjecture to nongeneric Arthur packets (this is joint work with Gross and Prasad). For GL(n), we describe some recent progress towards this conjecture by Max Gurevich.

Relative character asymptotics and applications

Paul Nelson
ETH Zurich
March 6, 2018
Abstract: Relative (or spherical) characters describe the restriction of a representation to a subgroup. They arise naturally in the study of periods of automorphic forms, e.g., in the setting of conjectures of Gan-Gross-Prasad and Ichino-Ikeda. I will discuss the problem of their asymptotic estimation, emphasizing some known results, open problems and applications.

Representations of p-adic groups

Jessica Fintzen
University of Michigan; Member, School of Mathematics
March 5, 2018

Abstract: The building blocks for complex representations of p-adic groups are called supercuspidal representations. I will survey what is known about the construction of supercuspidal representations, mention questions that remain mysterious until today, and explain some recent developments.

Supercuspidal L-packets

Tasho Kaletha
University of Michigan
March 5, 2018
Abstract: Harish-Chandra has given a simple and explicit classification of the discrete series representations of reductive groups over the real numbers. We will describe a very similar classification that holds for a large proportion of the supercuspidal representations of reductive groups over non-archimedean local fields (which we may call regular). The analogy runs deeper: there is a remarkable parallel between the characters of regular supercuspidal representations and the characters of discrete series representations of real reductive groups.