Hecke Operators on Drinfeld Cusp Forms

Abstract

In this paper, we study the Drinfeld cusp forms for $\Gamma_1(T)$ and $\Gamma(T)$ using Teitelbaum's interpretation as harmonic cocycles. We obtain explicit eigenvalues of Hecke operators associated to degree one prime ideals acting on the cusp forms for $\Gamma_1(T)$ of small weights and conclude that these Hecke operators are simultaneously diagonalizable. We also show that the Hecke operators are not diagonalizable in general for $\Gamma_1(T)$ of large weights, and not for $\Gamma(T)$ even of small weights. The Hecke eigenvalues on cusp forms for $\Gamma(T)$ with small weights are determined and the eigenspaces characterized.