Distinction and Base Change

TL;DR

This paper explores the relationship between distinguished representations of p-adic groups, functoriality, and base change, proving a conjecture for SL(n) and revealing new connections for GL(n).

Contribution

It proves Prasad's conjecture for SL(n) in the generic case and uncovers a novel link between distinction and base change in invariant linear forms.

Findings

Proof of Prasad's conjecture for SL(n) (generic case)

Discovery of base change influence on invariant form proportionality

New connection between distinction and base change for GL(n)

Abstract

An irreducible smooth representation of a $p$-adic group $G$ is said to be distinguished with respect to a subgroup $H$ if it admits a non-trivial $H$-invariant linear form. When $H$ is the fixed group of an involution on $G$ it is suggested by the works of Herv\'e Jacquet from the nineties that distinction can be characterized in terms of the principle of functoriality. If the involution is the Galois involution then a recent conjecture of Dipendra Prasad predicts a formula for the dimension of the space of invariant linear forms which once again involves base change. We will describe the proof of this conjecture (in the generic case) for $SL(n)$ which is joint work with Dipendra Prasad. Then we describe one more newly discovered connection between distinction and base change which is that base change information appears in the constant of proportionality between two natural invariant linear forms on a distinguished representation. This latter result is for discrete series for $GL(n)$ and is joint with Nadir Matringe. This paper is a report on the author's talk in the International Colloquium on Arithmetic Geometry held in January 2020 at TIFR Mumbai.