Simple supercuspidal representations of $\mathrm{GSp}_4$ and test vectors

TL;DR

This paper investigates simple supercuspidal representations of GSp4 over p-adic fields, computes explicit matrix coefficients and local integrals, and applies these results to global automorphic forms and the sup-norm problem.

Contribution

It provides explicit formulas for matrix coefficients and local integrals of simple supercuspidal representations of GSp4, and applies these to global period formulas and sup-norm bounds.

Findings

Representations have conductor exponent 5.

Explicit formulas for matrix coefficients and local integrals.

Existence of large-value paramodular newforms as p→∞.

Abstract

We consider simple supercuspidal representations of $\mathrm{GSp}_4$ over a $p$-adic field and show that they have conductor exponent 5. We study (paramodular) newvectors and minimal vectors in these representations, obtain formulas for their matrix coefficients, and compute key local integrals involving these as test vectors. Our local computations lead to several explicit global period formulas involving automorphic representations $\pi$ of $\mathrm{GSp}_4(\mathbb{A})$ whose local components (at ramified primes) are simple supercuspidal representations, and where the global test vectors are chosen to be (diagonal shifts of) newforms or automorphic forms of minimal type. As an analytic application of our work to the sup-norm problem, we show the existence of paramodular newforms on $\mathrm{GSp}_4(\mathbb{A})$ of conductor $p^5$ that take ``large values" on a fixed compact set as $p\rightarrow \infty$.