Discrete gauge symmetries in D-brane models

TL;DR

This paper investigates how discrete gauge symmetries naturally emerge in string theory brane models, particularly in MSSM constructions, and their role in forbidding dangerous couplings, with implications for particle physics phenomenology.

Contribution

It demonstrates that discrete gauge symmetries like R-parity and baryon triality arise naturally as remnants of continuous U(1) symmetries in string theory brane models, providing a fundamental origin.

Findings

Discrete Z_N gauge symmetries appear naturally in brane models.

These symmetries include R-parity and baryon triality.

Examples are provided in type IIA intersecting brane and F-theory GUT models.

Abstract

In particle physics model building discrete symmetries are often invoked to forbid unwanted or dangerous couplings. A classical example is the R-parity of the MSSM, which guarantees the absence of dimension four baryon- and lepton-number violating operators. Although phenomenologically useful, these discrete symmetries are, in the context of field theory, poorly motivated at a more fundamental level. Moreover, discrete {\em global} symmetries are expected to be violated in consistent couplings to quantum gravity, while their {\em gauged} versions are expected to actually exist. In this paper we study discrete gauge symmetries in brane models in string theory, and argue that they are fairly generic in this framework. In particular we study the appearance of discrete gauge symmetries in (MS)SM brane constructions in string theory, and show that a few discrete ${Z_N}$ gauge symmetries, including R-parity and {\it baryon triality}, appear naturally as remnants of continuous U(1) gauge symmetries with St\"uckelberg $N(B\wedge F)$ couplings. Interestingly, they correspond to the simplest anomaly-free discrete symmetries of the MSSM as classified in the early 90's. We provide a number of examples based on type IIA intersecting brane constructions with a (MS)SM spectrum. We also study the appearance of discrete generalizations of R-parity in unified SU(5) type IIA orientifolds and local F-theory SU(5) GUTs.