Gauge couplings in four-dimensional Type I string orbifolds

TL;DR

This paper calculates how gauge couplings in four-dimensional Type I string orbifold models depend on geometric moduli, including one-loop corrections and their implications for gauge unification and duality with heterotic strings.

Contribution

It provides explicit computations of threshold effects and tree-level couplings in Type I orbifold models with various supersymmetries, enhancing understanding of gauge coupling unification and dualities.

Findings

Threshold effects depend on geometric moduli.

Tree-level couplings to twisted closed string moduli are computed.

Results support duality between heterotic and Type I string theories.

Abstract

We compute threshold effects to gauge couplings in four-dimensional $Z_N$ orientifold models of type I strings with ${\cal N}=2$ and ${\cal N}=1$ supersymmetry, and study their dependence on the geometric moduli. We also compute the tree-level (disk) couplings of the open sector gauge fields to the twisted closed string moduli of the orbifold in various models and study their effects and that of the one-loop threshold corrections on gauge coupling unification. We interpret the results from the (supergravity) effective theory point of view and comment on the conjectured heterotic-type I duality