Linear independence of values of polylogarithms with periodic coefficients, outside the disk of convergence

Abstract

For any non-zero periodic function f\,: Z $\rightarrow$ C of period N ___ 1 and any non-zero algebraic number z\_0 that doesn't lie on a half-line [e^2i${\ell}$$π$/N , e^2i${\ell}$$π$/N $\infty$[, 0 ___ ${\ell}$ ___ N -1, we give a lower bound of order sqrt{s/log(s)} on the dimension of the Q(z\_0 )-vector space spanned by the numbers L(f, i, z\_0 )\,: sum\_{m=1}^$\infty$ f(m)z\_0^m/m^i. This generalizes a result Fischler proved in 2026, corresponding to f identically equal to 1 and |z\_0| ___ 1: in this case, the numbers L(f, i, z\_0 ) = Li\_i (z\_0 ) are polylogarithm values. Except for a finite number of cuts in the complex plane, our result still holds when |z\_0 | > 1, that is in a domain where the series definition above for the numbers L(f, i, z\_0 ) doesn't converge anymore, and we make sense of these numbers through analytic continuation. To obtain this result, we construct linear combinations of the numbers L(f, i, z\_0 ) using a refined version of Siegel's lemma, and we apply to them a linear independence criterion generalizing the one used by Fischler. To check the assumptions of this criterion, we rely on an integral representation of the polylogarithm functions and on a ''Shidlovskii lemma''.