Two properties of the partial theta function
For the partial theta function $\theta(q,z):=\sum_{j=0}^{\infty}q^{j(j+1)/2}z^j$, $q$, $z\in\mathbb{C}$, $|q|<1$, we prove that its zero locus is connected. This set is smooth at every point $(q^{\flat},z^{\flat})$ such that $z^{\flat}$ is a simple or double zero of $\theta(q^{\flat},.)$. For $q\in (0,1)$, $q\to 1^-$ and $a\geq e^{\pi}$, there are $o(1/(1-q))$ and $(\ln(a/e^{\pi}))/(1-q)+o(1/(1-q))$ real zeros of $\theta(q,.)$ in the intervals $[-e^{\pi},0)$ and $[-a,-e^{-\pi}]$ respectively (and none in $[0,\infty)$). For $q\in (-1,0)$, $q\to -1^+$ and $a\geq e^{\pi/2}$, there are $o(1/(1+q))$ real zeros of $\theta(q,.)$ in the interval $[-e^{\pi/2},e^{\pi/2}]$ and $(\ln(a/e^{\pi/2})/2)/(1+q)+o(1/(1+q))$ in each of the intervals $[-a,-e^{\pi/2}]$ and $[e^{\pi /2},a]$.
Authors
- Vladimir Petrov Kostov (ORCID: https://orcid.org/0000-0001-5836-2678)
Publication Details
- Journal
- Annual of Sofia University St Kliment Ohridski Faculty of Mathematics and Informatics
- Published
- 2025-12-05
- DOI
- https://doi.org/10.60063/gsu.fmi.112.77-91
- Primary Topic
- Advanced Mathematical Identities
- Type
- article
- Field-Weighted Citation Impact
- 0.00