Universality in string interactions

TL;DR

This paper provides evidence that the leading transcendental coefficients in the low-energy expansion of tree-level string scattering amplitudes are universal across all perturbative string theories, supported by checks up to seven points and underlying structural reasons.

Contribution

It conjectures and provides evidence for the universality of leading transcendental coefficients in the alpha'-expansion of tree-level string interactions across different string theories.

Findings

Universality holds up to seven points in scattering amplitudes.

The structure of disk integrals underpins this universality.

KLT-relations extend universality to closed-string sectors.

Abstract

In this letter, we provide evidence for universality in the low-energy expansion of tree-level string interactions. More precisely, in the alpha'-expansion of tree-level scattering amplitudes, we conjecture that the leading transcendental coefficient at each order in alpha' is universal for all perturbative string theories. We have checked this universality up to seven points and trace its origin to the ability to restructure the disk integrals of open bosonic string into those of the superstring. The accompanying kinematic functions have the same low-energy limit and do not introduce any transcendental numbers in their alpha'-corrections. Universality in the closed-string sector then follows from the KLT-relations.