Galois Representations and Automorphic Forms

http://math.ias.edu/files/seminars/GriffithsTwoTalks.pdf

Periods of automorphic forms over spherical subgroups tend to: (1) distinguish images of functorial lifts and (2) give information about L-functions. This raises the following questions, given a spherical variety X=H\G: Locally, which irreducible representations admit a non-zero H-invariant functional or, equivalently, appear in the space of functions on X? Globally, can the period over H of an automorphic form on G be related to some L-value?

The Bernstein center plays a role in the representation theory of locally profinite groups analogous to that played by the center of the group ring in the representation theory of finite groups. When F is a finite extension of Q_p, we discuss the Bernstein center of the category of smooth representations of GL_n(F) over the Witt vectors of an algebraically closed field of characteristic l not equal to p. We will prove results on the basic structure of the Bernstein center, and describe a conjecture that has implications for the local Langlands correspondence in algebraic families.

We attach Galois representations to automorphic representations on unitary groups whose weight (=component at infinity) is a holomorphic limit of discrete series. The main innovation is a new construction of congruences, using the Hasse Invariant, which avoids q-expansions and so is applicable in much greater generality than previous methods. Our result is a natural generalization of the classical Deligne-Serre Theorem on weight one modular forms and work of Taylor on GSp(4).