Two properties of the partial theta function
Classical Analysis and ODEs
2025-12-18 v1
Abstract
For the partial theta function θ(q,z):=∑j=0∞qj(j+1)/2zj, q, z∈C, ∣q∣<1, we prove that its zero set is connected. This set is smooth at every point (q♭,z♭) such that z♭ is a simple or double zero of θ(q♭,.). For q∈(0,1), q→1− and a≥eπ, there are o(1/(1−q)) and (ln(a/eπ))/(1−q)+o(1/(1−q)) real zeros of θ(q,.) in the intervals [−eπ,0) and [−a,−e−π] respectively (and none in [0,∞)). For q∈(−1,0), q→−1+ and a≥eπ/2, there are o(1/(1+q)) real zeros of θ(q,.) in the interval [−eπ/2,eπ/2] and (ln(a/eπ/2)/2)/(1+q)+o(1/(1+q)) in each of the intervals [−a,−eπ/2] and [eπ/2,a].
Cite
@article{arxiv.1911.08841,
title = {Two properties of the partial theta function},
author = {Vladimir Petrov Kostov},
journal= {arXiv preprint arXiv:1911.08841},
year = {2025}
}