The Whittaker functional is a shifted microstalk

TL;DR

This paper demonstrates that the Whittaker functional on nilpotent sheaves for a smooth projective curve corresponds to the shifted microstalk at a specific Hitchin moduli point, revealing its exactness and duality properties.

Contribution

It establishes a topological proof linking the Whittaker functional to microstalks, utilizing hyperbolic symmetry and vanishing cycles in the geometric Langlands context.

Findings

Whittaker functional equals shifted microstalk at a Hitchin point

The functional is exact for the perverse t-structure

It commutes with Verdier duality

Abstract

For a smooth projective curve $X$ and reductive group $G$, the Whittaker functional on nilpotent sheaves on $\text{Bun}_G(X)$ is expected to correspond to global sections of coherent sheaves on the spectral side of Betti geometric Langlands. We prove that the Whittaker functional calculates the (shifted) microstalk of nilpotent sheaves at the point in the Hitchin moduli where the Kostant section intersects the global nilpotent cone. In particular, the (shifted) Whittaker functional is exact for the perverse $t$-structure and commutes with Verdier duality. Our proof is topological and depends on the intrinsic local hyperbolic symmetry of $\text{Bun}_G(X)$. It is an application of a general result relating vanishing cycles to the composition of restriction to an attracting locus followed by vanishing cycles.