Rigid inner forms over local function fields

TL;DR

This paper extends the concept of rigid inner forms to local function fields, establishing a framework that supports the formulation of local Langlands conjectures for all connected reductive groups over such fields.

Contribution

It introduces a new cohomology set and a duality theorem for rigid inner forms over local function fields, enabling the formulation of endoscopic conjectures in this setting.

Findings

Defined a new cohomology set for rigid inner forms over local function fields.

Established an analogue of Tate-Nakayama duality for these forms.

Extended transfer factors to relate stable and $ ext{dot}s$-stable virtual characters.

Abstract

We generalize the concept of rigid inner forms, defined by Kaletha in [Kal16], to the setting of a local function field $F$ in order state the local Langlands conjectures for arbitrary connected reductive groups over $F$. To do this, we define for a connected reductive group $G$ over $F$ a new cohomology set $H^{1}(\mathcal{E}, Z \to G) \subset H_{\text{fpqc}}^{1}(\mathcal{E}, G)$ for a gerbe $\mathcal{E}$ attached to a class in $H_{\text{fppf}}^{2}(F, u)$ for a certain canonically-defined profinite commutative group scheme $u$, building up to an analogue of the classical Tate-Nakayama duality theorem. We define a relative transfer factor for an endoscopic datum serving a connected reductive group $G$ over $F$, and use rigid inner forms to extend this to an absolute transfer factor, enabling the statement of endoscopic conjectures relating stable virtual characters and $\dot{s}$-stable virtual characters for a semisimple $\dot{s}$ associated to a tempered Langlands parameter.