SV-map between Type I and Heterotic Sigma Models

TL;DR

This paper demonstrates that the single-valued projection relating heterotic and open string amplitudes also applies to their low-energy effective actions, linking their sigma model beta functions through a mathematical projection.

Contribution

It extends the single-valued projection concept from scattering amplitudes to the effective actions of heterotic and open strings via sigma model analysis.

Findings

Heterotic sigma model coefficients are single-valued projections of open string coefficients.

The relation holds at the level of individual Feynman diagrams and beta functions.

Summing over radial orderings on the world-sheet explains the single-valued projection.

Abstract

The scattering amplitudes of gauge bosons in heterotic and open superstring theories are related by the single-valued projection which yields heterotic amplitudes by selecting a subset of multiple zeta value coefficients in the $\alpha'$ (string tension parameter) expansion of open string amplitudes. In the present work, we argue that this relation holds also at the level of low-energy expansions (or individual Feynman diagrams) of the respective effective actions, by investigating the beta functions of two-dimensional sigma models describing world-sheets of open and heterotic strings. We analyze the sigma model Feynman diagrams generating identical effective action terms in both theories and show that the heterotic coefficients are given by the single-valued projection of the open ones. The single-valued projection appears as a result of summing over all radial orderings of heterotic vertices on the complex plane representing string world-sheet.