Infrared Regularization of Superstring Theory and the One-Loop Calculation of Coupling Constants

TL;DR

The paper addresses infrared divergences in four-dimensional N=1 superstring vacua by introducing an infrared regulator based on curved spacetime, implemented via a four-dimensional N=4 superconformal CFT block W_k^{(4)} that yields a mass gap and preserves some spacetime supersymmetry. It derives the exact one-loop effective action for constant background fields, making gauge, gravitational, and Yukawa couplings finite and computable, and formulates Infrared Flow Equations that relate scale changes to moduli. The authors provide explicit, modular-invariant expressions for one-loop gauge-coupling thresholds, including the universal back-reaction of gravity, and show how the regulator fixes ambiguities in low-energy string unification predictions. They further develop orbit-based techniques to extract moduli dependence and discuss implications for Yukawa couplings, higher-loop prospects, and non-perturbative dualities, laying a framework for connecting string theory to low-energy phenomenology.

Abstract

Infrared regularized versions of 4-D N=1 superstring ground states are constructed by curving the spacetime. A similar regularization can be performed in field theory. For the IR regularized string ground states we derive the exact one-loop effective action for non-zero U(1) or chromo-magnetic fields as well as gravitational and axionic-dilatonic fields. This effective action is IR and UV finite. Thus, the one-loop corrections to all couplings (gravitational, gauge and Yukawas) are unabiguously computed. These corrections are necessary for quantitative string superunification predictions at low energies. The one-loop corrections to the couplings are also found to satisfy Infrared Flow Equations.