Type IIB at eight derivatives: Five-Point Axio-Dilaton Couplings

TL;DR

This paper analyzes the eight-derivative effective action in Type IIB string theory, focusing on five-point interactions involving gravitons and axio-dilatons, and explores their perturbative and non-perturbative structures.

Contribution

It provides a detailed translation of five-point scattering amplitudes into contact terms and clarifies the non-perturbative completion of certain couplings.

Findings

Consistent with T-duality predictions at tree level.

Couplings with even/odd scalars are neutral/charged under SL(2,Z).

Identifies structures crucial for matching string corrections with M-theory.

Abstract

We study the Type IIB eight-derivative effective Lagrangian beyond the quartic level, focusing on interactions involving gravitons and axio-dilatons. We show how to translate five-point scattering amplitudes into genuine five-point contact terms and extract all perturbative contributions to the effective action. Our result is consistent with T-duality predictions at tree level in the NSNS sector. We find that couplings with an even/odd number of scalars are neutral/charged under $\mathrm{SL}(2,\mathbb{Z})$, and use this feature to deduce their non-perturbative completion. The mixed NSNS/RR structures that cannot be deduced from the pure NSNS sector allow us to unambiguously fix the kinematics, which turns out to be the same for tree level and one loop. In Type IIA, these structures are essential for establishing agreement of string-theoretic corrections with the circle reduction of M-theory higher-derivative couplings.