On Atkin and Swinnerton-Dyer congruence relations (3)

Abstract

In the previous two papers with the same title ([LLY05] by W.C. Li, L. Long, Z. Yang and [ALL05] by A.O.L. Atkin, W.C. Li, L. Long), the authors have studied special families of cuspforms for noncongruence arithmetic subgroups. It was found that the Fourier coefficients of these modular forms at infinity satisfy three-term Atkin and Swinnerton-Dyer congruence relations which are the $p$-adic analogue of the three-term recursions satisfied by the coefficients of classical Hecke eigenforms. In this paper, we first consider Atkin and Swinnerton-Dyer type congruences which generalize the three-term congruences above. These weaker congruences are satisfied by cuspforms for special noncongruence arithmetic subgroups. Then we will exhibit an infinite family of noncongruence cuspforms, each of which satisfies three-term Atkin and Swinnerton-Dyer type congruences for almost every prime $p$. Finally, we will study a particular space of noncongruence cuspforms. We will show that the attached $l$-adic Scholl representation is isomorphic to the $l$-adic representation attached to a classical automorphic form. Moreover, for each of the four residue classes of odd primes modulo 12 there is a basis so that the Fourier coefficients of each basis element satisfy three-term Atkin and Swinnerton-Dyer congruences in the stronger original sense.