Closed-form evaluations of log-sine integrals and Ap\'ery-like sums in terms of polylogarithms

Abstract

We present a new systematic method for evaluating generalized log-sine integrals in terms of polylogarithms. Our approach is based on an identity connecting ordinary generating functions of polylogarithms to integrals involving the sine function. This method provides closed-form expressions for log-sine integrals of weight up to 4 using only classical polylogarithms, while higher weights require Nielsen polylogarithms. Later we generalize this identity and show how it gives rise to numerous Ap\'ery-like formulae extending results of Koecher, Leshchiner and others. We also derive hyperbolic analogues and recover several functional equations between Nielsen polylogarithms. In the process, we derive new parametric identities similar to those given by Saha and Sinha.