Discrete Gauge Symmetries in Discrete MSSM-like Orientifolds

TL;DR

This paper investigates the origin of discrete gauge symmetries in string theory models related to the MSSM, identifying conditions under which these symmetries emerge and their implications for particle physics phenomenology.

Contribution

It provides an explicit construction of axion-U(1) couplings in Gepner models and applies this to identify discrete symmetries in MSSM-like string models.

Findings

Discrete Z_2 and Z_3 symmetries found in some models.

Rare occurrence of these symmetries, about a few percent.

Examples of models with symmetries that forbid certain B and L violating couplings.

Abstract

Motivated by the necessity of discrete Z_N symmetries in the MSSM to insure baryon stability, we study the origin of discrete gauge symmetries from open string sector U(1)'s in orientifolds based on rational conformal field theory. By means of an explicit construction, we find an integral basis for the couplings of axions and U(1) factors for all simple current MIPFs and orientifolds of all 168 Gepner models, a total of 32990 distinct cases. We discuss how the presence of discrete symmetries surviving as a subgroup of broken U(1)'s can be derived using this basis. We apply this procedure to models with MSSM chiral spectrum, concretely to all known U(3)xU(2)xU(1)xU(1) and U(3)xSp(2)xU(1)xU(1) configurations with chiral bi-fundamentals, but no chiral tensors, as well as some SU(5) GUT models. We find examples of models with Z_2 (R-parity) and Z_3 symmetries that forbid certain B and/or L violating MSSM couplings. Their presence is however relatively rare, at the level of a few percent of all cases.