Positivity rigidity conjecture for a binomial finite-difference sum

Fix sN+s\in\mathbb{N}^+, qR{0}q\in\mathbb{R}\setminus\{0\}, q~R\widetilde{q}\in\mathbb{R} with q~>0\widetilde{q}>0, and real numbers pmp_m for m=0,1,,s+1m=0,1,\ldots,s+1. Suppose that, for every k=0,1,,s+1k=0,1,\ldots,s+1,

m=0min(k,s)(s1+kms1)pmqm(q~)km0.\sum_{m=0}^{\min(k,s)}\binom{s-1+k-m}{s-1}p_mq^m(-\widetilde{q})^{k-m}\geq 0.

Positivity rigidity conjecture. Then p00p_0\geq 0, and for m=1,2,,s+1m=1,2,\ldots,s+1,

pm=p0(sm)(q~q)m.p_m=p_0\binom{s}{m}\left(\frac{\widetilde{q}}{q}\right)^m.

Moreover, the sum equals p0p_0 for k=0k=0 and 00 for k=1,2,,s+1k=1,2,\ldots,s+1. The conjecture was verified by Mathematica for 1s101\leq s\leq 10 and proved manually for s=2s=2, but its general status is unresolved.

Sources & referencesView supporting material

Primary source

Lajos Loczi and David I. Ketcheson, “Rational functions with maximal radius of absolute monotonicity”, arXiv:1303.6651 (2013).

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