Period functions for vector-valued Maass cusp forms of real weight, with an application to Jacobi Maass cusp forms

TL;DR

This paper introduces a new framework of vector-valued period functions for Maass cusp forms of real weight, establishing a linear isomorphism with these forms and extending the concept to Jacobi Maass cusp forms.

Contribution

It defines vector-valued period functions for Maass cusp forms with real weight and proves a linear isomorphism between these functions and the forms, also applying the theory to Jacobi Maass cusp forms.

Findings

Established a cohomological approach to relate Maass cusp forms and period functions.

Generalized period functions to solutions of finite-term functional equations.

Extended the concept of period functions to Jacobi Maass cusp forms.

Abstract

For vector-valued Maass cusp forms for~$SL_2(\mathbb{Z})$ with real weight~$k\in\mathbb{R}$ and spectral parameter $s\in\mathbb{C}$, $\mathrm{Re} s\in (0,1)$, $s\not\equiv \pm k/2$ mod $1$, we propose a notion of vector-valued period functions, and we establish a linear isomorphism between the spaces of Maass cusp forms and period functions by means of a cohomological approach. The period functions are a generalization of those for the classical Maass cusp forms, being solutions of a finite-term functional equation or, equivalently, eigenfunctions with eigenvalue $1$ of a transfer operator deduced from the geodesic flow on the modular surface. We apply this result to deduce a notion of period functions and related linear isomorphism for Jacobi Maass forms of weight $k+1/2$ for the semi-direct product of $SL_2(\mathbb{Z})$ with the integer points $Hei(\mathbb{Z})$ of the Heisenberg group.