Characterization of positivity by completely monotone Dirichlet-series products

Let ζ(s)\zeta(s) be a generalized Dirichlet series absolutely convergent on the half-plane {z:Rez1}\{z: \operatorname{Re} z\ge 1\}, and suppose that it has a simple zero at s=1s=1. A generalized Dirichlet series has positive coefficients if all its coefficients are positive; a function is completely monotone on (1,)(1,\infty) if it has derivatives of every order there and (1)nf(n)(s)0(-1)^n f^{(n)}(s)\ge 0 for every integer n0n\ge 0. The conjecture. ζ(s)\zeta(s) is positive on (1,)(1,\infty) if and only if there exists a generalized Dirichlet series ζ2(s)≢0\zeta_2(s)\not\equiv 0 with positive coefficients, absolutely convergent on the half-plane {z:Rez1}\{z: \operatorname{Re} z\ge 1\}, such that

ζ(s)ζ2(s)s(s1)\frac{\zeta(s)\zeta_2(s)}{s(s-1)}

is completely monotone on (1,)(1,\infty). This conjecture extends finite-dimensional characterizations related to trumping to generalized Dirichlet series in infinite dimensions; the supplied text does not establish the equivalence, so its resolution remains open.

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Primary source

Rajesh Pereira and Sarah Plosker, “Extending a characterization of majorization to infinite dimensions”, arXiv:1405.2845 (2014).

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