One-loop fermionic string amplitudes with up to four massless (bosonic) external legs are calculated in Polyakov's approach and shown to agree with the ones in operator formalism. Some of the ingredients necessary to prove the vanishing of the multiloop amplitudes with up to three external legs are also discussed. © 1986.
Namazie, M. A., Narain, K. S., & Sarmadi, M. H. (1986). Fermionic string loop amplitudes with external bosons. Physics Letters B, 177(3–4), 329–334. https://doi.org/10.1016/0370-2693(86)90762-8