Sokal's simplicity problem for the partial theta function

Let

Θ0(z;q)=n=0qn(n1)2zn,\Theta_0(z;q)=\sum_{n=0}^\infty q^{\frac{n(n-1)}2}z^n,

where q~0.3092493386\widetilde q\approx 0.3092493386 is the positive threshold described in the source. Sokal's partial-theta problem. Is it true that all zeros of Θ0(z;q)\Theta_0(z;q) remain simple within the open disk q<q~|q|<\widetilde q? The source gives partial confirmation, proving simplicity and distinct absolute values for purely imaginary parameters in a smaller range, but the full disk question remains open.

Sources & referencesView supporting material

Primary source

Alexander Dyachenko, “One helpful property of functions generating Pólya frequency sequences”, arXiv:1506.07689 (2015).

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