Universality of Gauge Thresholds in Non-Supersymmetric Heterotic Vacua

TL;DR

This paper investigates the one-loop gauge threshold corrections in non-supersymmetric heterotic string vacua, revealing universal behaviors and singularities linked to BPS-like states, regardless of K3 orbifold realizations.

Contribution

It demonstrates the universality of gauge threshold differences in non-supersymmetric heterotic vacua and analyzes their singularities at special moduli space points.

Findings

Threshold differences are BPS saturated and universal across orbifold realizations.

Thresholds develop infrared logarithmic singularities at special moduli points.

Threshold corrections include contributions from the RNS sector excitations.

Abstract

We compute one-loop threshold corrections to non-abelian gauge couplings in four-dimensional heterotic vacua with spontaneously broken $\cal N = 2 \to \cal N = 0$ supersymmetry, obtained as Scherk-Schwarz reductions of six-dimensional K3 compactifications. As expected, the gauge thresholds are no-longer BPS protected, and receive contributions also from the excitations of the RNS sector. Remarkably, the difference of thresholds for non-abelian gauge couplings is BPS saturated and exhibits a universal behaviour independently of the orbifold realisation of K3. Moreover, the thresholds and their difference develop infra-red logarithmic singularities whenever charged BPS-like states, originating from the twisted RNS sector, become massless at special loci in the classical moduli space.