String-Unification, Universal One-Loop Corrections and Strongly Coupled Heterotic String Theory

TL;DR

This work derives universal and gauge-dependent string threshold corrections in perturbative heterotic string theory with continuous Wilson lines and analyzes their impact on gauge–gravity unification. It shows that unification can be achieved at modest moduli values and clarifies how gauge-group dependent thresholds, together with universal corrections controlled by the holomorphic gauge kinetic function, determine low-energy observables and the GUT scale. The authors connect threshold corrections to anomaly cancellation via Green–Schwarz terms and argue, based on holomorphy, that perturbative results may extend to the strongly coupled regime relevant to M-theory, albeit with possible nonperturbative contributions. They also provide explicit expressions for thresholds in Wilson-line backgrounds, highlighting how Wilson lines influence the f-function and the conditions for reliable extrapolation to strong coupling. Overall, the paper establishes a robust framework linking perturbative thresholds, duality, and anomaly structure to both unification physics and potential strong-coupling interpretations.

Abstract

We derive the universal threshold corrections in heterotic string theory including a continuous Wilson line. Unification of gauge and gravitational couplings is shown to be possible even within perturbative string theory. The relative importance of gauge group dependent and independent thresholds on unification is clarified. Equipped with these results we can then attempt an extrapolation to the strongly coupled heterotic string -- M-theory. We argue that such an extrapolation might be meaningful because of the holomorphic structure of the gauge coupling function and the close connection of the threshold corrections to the anomaly cancelation mechanism.