Superstring Amplitudes in Genus 0 and Double Copy

This is joint work with Clément Dupont. Motivated by double-copy  (Kawai-Lewellen-Tye) formulae relating open and closed superstring amplitudes at tree-level, I will explain a general double-copy formula for period integrals on algebraic varieties and its relation to single-valued functions. As an application, we deduce a conjecture of Stieberger which states that the passage from open to closed amplitudes in string perturbation theory at genus zero is given by the so-called single-valued map.