Yu-tin HuangHynek PaulMichele Santagata2025-01-142025-01-142024-11-20https://scholars.lib.ntu.edu.tw/handle/123456789/724812We describe a general formalism based on the partial-wave decomposition to compute the iterative s-channel discontinuity of four-point amplitudes at any loop order. As an application, we focus on the low-energy expansions of type I and II superstring amplitudes. Besides providing new results for their leading and sub-leading logarithmic contributions beyond genus one, our approach elucidates the general structure of non-analytic threshold terms. In the case of open strings, the use of orthogonal colour projectors allows us to efficiently compute all contributions from different worldsheet topologies at a given loop order.Scattering AmplitudesSuperstrings and Heterotic Stringsjournal article10.1007/jhep11(2024)117