All order alpha'-expansion of superstring trees from the Drinfeld associator
arXiv:1304.7304 · doi:10.1103/PhysRevD.89.066014
Abstract
We derive a recursive formula for the alpha'-expansion of superstring tree amplitudes involving any number N of massless open string states. String corrections to Yang-Mills field theory are shown to enter through the Drinfeld associator, a generating series for multiple zeta values. Our results apply for any number of spacetime dimensions or supersymmetries and chosen helicity configurations.
6 pages, LaTeX; v2: Final version to appear in PRD