An extension of Deligne-Henniart's twisting formula and its applications

Abstract

Let $F/\bbQ_p$ be a non-Archimedean local field, and $G_F$ be the absolute Galois group of $F$. Let $\rho_1$ and $\rho_2$ be two finite-dimensional complex representations of $G_F$. Let $\psi$ be a nontrivial additive character of $F$. Then, the question is: What is the twisting formula for the root number $W(\rho_1\otimes\rho_2,\psi)$?} In general, the answer to this question is not yet known. However, if one of $\rho_i \quad(i=1,2)$ is one-dimensional with ``sufficiently'' large conductor, then in [13], Deligne gave a twisting formula for $W(\rho_1\otimes\rho_2,\psi)$. Later, in [12], Deligne and Henniart gave a general twisting formula for a {\it zero}-dimensional virtual representation twisted by a finite-dimensional representation of $G_F$. In this paper, we first extend Deligne's twisting formula for U-isotropic Heisenberg representation of dimension prime $p$, then we further extend Deligne-Henniart's result. Finally, we provide two very important applications of our twisting formula: -- (i) invariant formula for the local root numbers for U-isotropic Heisenberg representations, and (ii) a converse theorem on the Galois side.