Abstract

Let \mathrm{F}/\mathrm{F}_{\mathsf{o}} be a quadratic extension of non-archimedean locally compact fields of odd residual characteristic and \sigma be its non-trivial automorphism. We show that any \sigma -self-dual cuspidal representation of \operatorname{GL}_n(\mathrm{F}) contains a \sigma -self-dual Bushnell–Kutzko type. Using such a type, we construct an explicit test vector for Flicker's local Asai L-function of a \operatorname{GL}_n(\mathrm{F}_\mathsf{o}) -distinguished cuspidal representation and compute the associated Asai root number. Finally, by using global methods, we compare this root number to Langlands–Shahidi's local Asai root number, and more generally we compare the corresponding epsilon factors for any cuspidal representation.

Highlights

  • Let F/Fo be a quadratic extension of locally compact non-archimedean fields of odd residual characteristic p and let σ denote the non-trivial element of Gal(F/Fo)

  • Our proof of Proposition 1.7 is based on a result of Ok [41] proved for any irreducible complex representation of G, and which we prove for any cuspidal representation of G with coefficients in R in Appendix B

  • When π is in addition unramified, we prove that it is equal to the local Asai epsilon factor LASs(s, π, ψo) obtained via the Langlands–Shahidi method

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Summary

Introduction

Let F/Fo be a quadratic extension of locally compact non-archimedean fields of odd residual characteristic p and let σ denote the non-trivial element of Gal(F/Fo). Consider a cuspidal (irreducible, smooth, complex) representation π of G, and suppose that its Asai L-function LAs(s, π) is non-trivial. A σ-self-dual cuspidal representation π of G with coefficients in R is distinguished if and only if any generic σ-self-dual type (J, λ) contained in π is distinguished, that is, the space HomJ∩Gσ (λ, 1) is non-zero. Let π be a distinguished cuspidal representation of G, and (J, λ) be a generic σ-self-dual type contained in π. The starting point of both papers is the σ-self-dual type theorem for cuspidal R-representations, namely Theorem 1.5, which is proved in Section 4 below. For complex representations, in which case all cuspidal representations are supercuspidal, this implies the two results stated in Paragraph 7.1 (i.e. Theorem 7.1 and Proposition 7.2) which we use in the proof of Theorem 1.1. We use Proposition 5.8, which is proved in [47], for any σ-self-dual supercuspidal R-representation of G

Notation
Preliminaries on simple types
Simple strata
Simple characters and endo-classes
Simple types and cuspidal representations
The σ-self-dual type theorem
The endo-class
A prelude
The tame parameter field
The maximal and totally wild case
The maximal case
The general case
Classification of σ-self-dual types
A counterexample in the semisimple case
Generic σ-self-dual types
Distinguished linear forms and Whittaker functions
Distinction and dichotomy
Definition of the integrals
A decomposition of the integral
Test vectors
Flicker–Kable root numbers for cuspidal representations
Comparing Asai epsilon factors
Changing the additive character
Unramified representations
The local factors at split places
Global factors
Cuspidal representations
A Some remarks in positive characteristic
A modular version of a result of Bruhat on equivariant distributions
A modular version of a result of Kable
A modular version of a result of Ok for cuspidal representations

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