The $p$-adic constant for mock modular forms associated to CM forms

Abstract

Let $g \in S_{k}(\Gamma_{0}(N))$ be a normalized newform and $f$ be a harmonic Maass form that is good for $g$. The holomorphic part of $f$ is called a mock modular form and denoted by $f^{+}$. For odd prime $p$, K. Bringmann, P. Guerzhoy, and B. Kane obtained a $p$-adic modular form of level $pN$ from $f^{+}$ and a certain $p$-adic constant $\alpha_{g}(f)$. When $g$ has complex multiplication by an imaginary quadratic field $K$ and $p$ is split in $\mathcal{O}_{K}$, it is known that $\alpha_{g}(f)$ is zero. On the other hand, we do not know much about $\alpha_{g}(f)$ for an inert prime $p$. In this paper, we prove that $\alpha_{g}(f)$ is a $p$-adic unit when $p$ is inert in $\mathcal{O}_{K}$ and $\dim_{\mathbb{C}}S_{k}(\Gamma_{0}(N))=1$.