A Note On Non-ordinary Primes

Abstract

Suppose that $O_L$ is the ring of integers of a number field $L$, and suppose that $f(z)={\sum }_{n=1}^{\infty }{a}_f(n)q^n\in S_k\cap O_L[[q]]$ (note: $q:=e^{2\pi iz}$) is a normalized Hecke eigenform for ${\mathrm{SL}}_2(\mathbb{Z})$. We say that $f$ is non-ordinary at a prime $p$ if there is a prime ideal $\mathfrak{p}\subset O_L$ above $p$ for which $a_f(p)\equiv 0(mod\mathfrak{p})$. For any finite set of primes $S$, we prove that there are normalized Hecke eigenforms which are non-ordinary for each $p\in S$. The proof is elementary and follows from a generalization of work of Choie, Kohnen and the third author.

arXiv comment7 pages