Subleading Soft Factor for String Disk Amplitudes

TL;DR

This paper proves that the subleading soft factor in superstring disk amplitudes matches the field theory result without string corrections, and discusses implications for closed string theory.

Contribution

It demonstrates the absence of '-corrections to the subleading soft factor in superstring disk amplitudes, linking string and field theory results.

Findings

No '-corrections to the subleading soft factor in superstring amplitudes

Potential extension of results to closed string theory via KLT relations

Insights into the universality of soft factors across string theories

Abstract

We investigate the behavior of superstring disk scattering amplitudes in the presence of a soft external momentum at finite string tension. We prove that there are no $\alpha'$-corrections to the field theory form of the subleading soft factor $S^{(1)}$. At the end of this work, we also comment on the possibility to find the corresponding subleading soft factors in closed string theory using our result and the KLT relations.