On gauge couplings and thresholds in Type I Gepner models and otherwise

TL;DR

The paper develops compact, general formulae for tree-level gauge couplings and their one-loop thresholds in Type I string vacua based on genuinely interacting ${\mathcal N}=2$ SCFTs, notably Gepner models, and illustrates the construction with the Quintic. It employs the background-field method and RCFT data, including elliptic indices and tadpole constraints, to derive moduli-dependent gauge couplings and threshold corrections from ${\mathcal N}=2$ sectors, with explicit expressions in Gepner contexts. The Quintic example yields a concrete gauge group $SO(12)\times SO(20)$ and provides beta-function and threshold analyses, while the discussion of Weinberg angle embedding and magnetized/coisotropic D-branes points to rich phenomenological directions. Overall, the work links worldsheet RCFT structures to low-energy gauge couplings, offering a framework for exploring gauge coupling unification and moduli effects in Calabi–Yau Gepner compactifications.

Abstract

We derive general formulae for tree level gauge couplings and their one-loop thresholds in Type I models based on genuinely interacting internal N=2 SCFT's, such as Gepner models. We illustrate our procedure in the simple yet non-trivial instance of the Quintic. We briefly address the phenomenologically more relevant issue of determining the Weinberg angle in this class of models. Finally we initiate the study of the correspondence between `magnetized' or `coisotropic' D-branes in Gepner models and twisted representations of the underlying N=2 SCA.