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A triple integral analog of a multiple zeta value

A triple integral analog of a multiple zeta value
Tewodros Amdeberhan, Victor H. Moll, Armin Straub, Christophe VignatPreprint — 2020

Abstract

We establish the triple integral evaluation \[ \int_{1}^{\infty} \int_{0}^{1} \int_{0}^{1} \frac{dz \, dy \, dx}{x(x+y)(x+y+z)} = \frac{5}{24} \zeta(3), \] as well as the equivalent polylogarithmic double sum \[ \sum_{k=1}^{\infty} \sum_{j=k}^{\infty} \frac{(-1)^{k-1}}{k^{2}} \, \frac{1}{j \, 2^{j}} = \frac{13}{24} \zeta(3). \] This double sum is related to, but less approachable than, similar sums studied by Ramanujan. It is also reminiscent of Euler's formula \(\zeta(2,1) = \zeta(3)\), which is the simplest instance of duality of multiple polylogarithms. We review this duality and apply it to derive a companion identity. We also discuss approaches based on computer algebra. All of our approaches ultimately require the introduction of polylogarithms and nontrivial relations between them. It remains an open challenge to relate the triple integral or the double sum to \(\zeta(3)\) directly.

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BibTeX

@article{tripleintegral-zeta3-2020,
    author = {Tewodros Amdeberhan and Victor H. Moll and Armin Straub and Christophe Vignat},
    title = {A triple integral analog of a multiple zeta value},
    journal = {Preprint},
    year = {2020},
}