The structure of the R^8 term in type IIB string theory

TL;DR

This paper investigates the R^8 interaction in type IIB string theory, analyzing its structure, perturbative and non-perturbative contributions, and its relation to supersymmetry and dualities, revealing new insights into higher-derivative corrections.

Contribution

It identifies the R^8 interaction as a non-BPS term in the effective action, analyzes its amplitude structure, and explores its perturbative and instanton contributions, expanding understanding of string theory corrections.

Findings

R^8 interaction is in the same supermultiplet as G^8 R^4.

R^8 receives contributions at one and two loops, and from D-instanton-anti-instanton backgrounds.

Amplitude analysis shows intricate pole structure and transcendentality.

Abstract

Based on the structure of the on-shell linearized superspace of type IIB supergravity, we argue that there is a non--BPS 16 derivative interaction in the effective action of type IIB string theory of the form (t_8 t_8 R^4)^2, which we call the R^8 interaction. It lies in the same supermultiplet as the G^8 R^4 interaction. Using the KLT relation, we analyse the structure of the tree level eight graviton scattering amplitude in the type IIB theory, which leads to the R^8 interaction at the linearized level. This involves an analysis of color ordered multi-gluon disc amplitudes in the type I theory, which shows an intricate pole structure and transcendentality consistent with various other interactions. Considerations of S-duality show that the R^8 interaction receives non-analytic contributions in the string coupling at one and two loops. Apart from receiving perturbative contributions, we show that the R^8 interaction receives a non-vanishing contribution in the one D-instanton-anti-instanton background at leading order in the weak coupling expansion.