Running Gauge Couplings and Thresholds in the Type II Superstring

Abstract

A distinctive feature of string unification is the possibility of unification by a non-simply-laced group. This occurs most naturally in four dimensional type~II string models where the gauge symmetry is realized by Kac-Moody algebras at different levels. We investigate the running coupling constants and the one-loop thresholds for such general models. As a specific case, we examine a $\mathrm{SU}(3)\times \mathrm{U}(1)\times \mathrm{U}(1)$ model and find that the threshold corrections lead to a small $6\%$ increase in the unification scale.

12 pages, IFP-432-UNC