On the real zeros of depth 1 quasimodular forms

Abstract

We discuss the critical points of modular forms, or more generally the zeros of quasimodular forms of depth $1$ for ${\mathrm{PSL}}_2(\mathbb{Z})$. In particular, we consider the derivatives of the unique weight $k$ modular forms $f_k$ with the maximal number of consecutive zero Fourier coefficients following the constant $1$. Our main results state that (1) every zero of a depth $1$ quasimodular form near the derivative of the Eisenstein series in the standard fundamental domain lies on the geodesic segment $\{z\in \mathbb{H}:\Re (z)=1/2\}$, and (2) more than half of zeros of $f_k$ in the standard fundamental domain lie on the geodesic segment $\{z\in \mathbb{H}:\Re (z)=1/2\}$ for large enough $k$ with $k\equiv 0(\mathrm{mod}12)$.

19 pages, 1 figure