On strong multiplicity one for automorphic representations

Abstract

We extend the strong multiplicity one theorem of Jacquet, Piatetski-Shapiro and Shalika. Let $\pi$ be a unitary, cuspidal, automorphic representation of $GL_n(\A_K)$. Let $S$ be a set of finite places of $K$, such that the sum $\sum_{v\in S}Nv^{-2/(n^2+1)}$ is convergent. Then $\pi$ is uniquely determined by the collection of the local components $\{\pi_v\mid v\not\in S, ~v \~\text{finite}\}$ of $\pi$. Combining this theorem with base change, it is possible to consider sets $S$ of positive density, having appropriate splitting behavior with respect to solvable extensions of $K$, and where $\pi$ is determined upto twisting by a character of the Galois group of $L$ over $K$.