# Soft Theorems in Superstring Theory

## TL;DR

This paper proves soft graviton theorems in superstring theories using superstring field theory, establishing results for tree amplitudes with arbitrary external states and discussing extensions to loop amplitudes.

## Contribution

It provides a novel proof of soft graviton theorems in superstring theory for arbitrary external states without restrictions on mass or spin.

## Key findings

- Proved subleading soft graviton theorem for heterotic and type II string tree amplitudes.
- Proved leading soft graviton theorem for multiple soft gravitons.
- Discussed extension to loop amplitudes and related technical challenges.

## Abstract

We use insights from superstring field theory to prove the subleading soft graviton theorem for tree amplitudes of (compactified) heterotic and type II string theories for arbitrary number of finite energy NS (NSNS) sector external states but only one soft graviton. We also prove the leading soft graviton theorem in these theories for arbitrary number of external soft gravitons. In our analysis there is no restriction on the mass and spin of the finite energy external states. This method can also be used to give a proof of the subleading soft graviton theorem for tree amplitudes in quantum field theories coupled to gravity with generic interactions. We discuss the technical issue involved in extending this analysis to loop amplitudes of superstring theory including Ramond sector external states, and its possible resolution.