Values of Harmonic Weak Maass forms on Hecke orbits

Abstract

Let $q:=e^{2\pi iz}$, where $z\in \mathbb{H}$. For an even integer $k$, let $f(z):=q^h{\prod }_{m=1}^{\infty }(1-q^m{)}^{c(m)}$ be a meromorphic modular form of weight $k$ on ${\Gamma }_0(N)$. For a positive integer $m$, let $T_m$ be the $m$th Hecke operator and $D$ be a divisor of a modular curve with level $N$. Both subjects, the exponents $c(m)$ of a modular form and the distribution of the points in the support of $T_m.D$, have been widely investigated. When the level $N$ is one, Bruinier, Kohnen, and Ono obtained, in terms of the values of $j$-invariant function, identities between the exponents $c(m)$ of a modular form and the points in the support of $T_m.D$. In this paper, we extend this result to general ${\Gamma }_0(N)$ in terms of values of harmonic weak Maass forms of weight $0$. By the distribution of Hecke points, this applies to obtain an asymptotic behaviour of convolutions of sums of divisors of an integer and sums of exponents of a modular form.