On the soft limit of tree-level string amplitudes

TL;DR

This paper investigates the behavior of string scattering amplitudes when one external particle becomes soft, analyzing both open and closed string cases at tree level with massless and massive states.

Contribution

It provides a detailed analysis of the soft limit behavior of tree-level string amplitudes using various computational techniques for 4-point functions.

Findings

Characterizes the soft behavior of open and closed string amplitudes.

Identifies differences in soft limits between massless and massive states.

Uses multiple methods to compute 4-point amplitudes.

Abstract

We study the soft behavior of string scattering amplitudes at three level with massless and massive external insertions, relying on different techniques to compute 4-points amplitudes respectively with open or closed strings.