A domain containing all zeros of the partial theta function

Abstract

We consider the partial theta function, i.e. the sum of the bivariate series $\theta (q,z):=\sum_{j=0}^{\infty}q^{j(j+1)/2}z^j$ for $q\in (0,1)$, $z\in \mathbb{C}$. We show that for any value of the parameter $q\in (0,1)$ all zeros of the function $\theta (q,.)$ belong to the domain $\{ {\rm Re}~z<0, |{\rm Im}~z|\leq 132\}$$\cup$$\{ {\rm Re}~z\geq 0, |z|\leq 18\}$.