Analog of theta-lifting for a curve over dual numbers over a finite field

TL;DR

This paper extends the theory of automorphic functions and theta-lifting to curves over dual numbers over finite fields, demonstrating how strongly cuspidal functions can be constructed via theta-lifting in this setting.

Contribution

It introduces a new framework for theta-lifting on curves over dual numbers over finite fields and shows how to construct all strongly cuspidal functions through this method.

Findings

Theta-lifting can be understood via orbit decomposition of automorphic functions.

All strongly cuspidal functions are constructible using theta-lifting.

The framework generalizes automorphic function theory to dual number curves.

Abstract

We continue the study of automorphic functions associated with a curve $C$ over the ring $k[\epsilon]/(\epsilon^2)$, where $k$ is a finite field, begun in arXiv:2303.16259. Namely, we study an example of theta-lifting in this framework and show that it can be understood in terms of the orbit decomposition of the space of automorphic functions $\mathcal{S}(\rm{SL}_2(F)\backslash \rm{SL}_2(\mathbb{A}_C))$ introduced in loc.cit. We prove that all strongly cuspidal functions in $\mathcal{S}(\rm{SL}_2(F)\backslash \rm{SL}_2(\mathbb{A}_C))$ can be constructed using theta-lifting for an appropriate double covering $\tilde{C}\to C$.