Computations of Galois Representations Associated to Modular Forms

Abstract

We propose an improved algorithm for computing mod $\ell$ Galois representations associated to a cusp form $f$ of level one. The proposed method allows us to explicitly compute the case with $\ell =29$ and $f$ of weight $k=16$, and the cases with $\ell =31$ and $f$ of weight $k=12,20,22$. All the results are rigorously proved to be correct. As an example, we will compute the values modulo $31$ of Ramanujan's tau function at some huge primes up to a sign. Also we will give an improved higher bound on Lehmer's conjecture for Ramanujan's tau function.

arXiv commentThis paper has been published in Acta Arithmetica