Gauge and Gravitational Couplings from Modular Orbits in Orbifold Compactifications

TL;DR

This paper investigates how modular functions influence gauge and gravitational couplings in heterotic string orbifold compactifications, providing insights into singularities and the stringy Higgs effect.

Contribution

It introduces a framework for understanding the role of modular functions in one-loop couplings and clarifies conditions for singularities in the moduli space of heterotic orbifolds.

Findings

Identifies limits for the existence of states causing singularities.

Provides evidence for the stringy Higgs effect.

Clarifies the role of modular functions in couplings.

Abstract

We discuss the appearance of modular functions at the one-loop gauge and gravitational couplings in (0,2) non-decomposable N=1 four dimensional orbifold compactifications of the heterotic string. We define the limits for the existence of states causing singularities in the moduli space in the perturbative regime for a generic vacuum of the heterotic string. The "proof" provides evidence for the explanation of the stringy Higgs effect.