Gauged Baryon and Lepton Number in MSSM_4 Brane Worlds

TL;DR

This paper explores a D-brane model with an extra unbroken U(1) gauge symmetry that encodes baryon and lepton numbers, offering new ways to address proton decay and neutrino masses in the MSSM framework.

Contribution

It demonstrates that the additional U(1) gauge symmetries in a D-brane MSSM model can naturally correspond to baryon and lepton number, providing novel mechanisms for baryogenesis and neutrino mass suppression.

Findings

The extra U(1)_B and U(1)_L symmetries can be spontaneously broken at lower scales.

These symmetries help preserve baryogenesis.

They explain the smallness of right-handed neutrino Majorana masses.

Abstract

A recent D-brane model designed to accommodate a phenomenologically acceptable fourth generation of chiral fermions was noted to produce an unexpected additional unbroken nonanomalous U(1) gauge group at the string scale. We show that the corresponding charges acting on MSSM fields count baryon and lepton numbers. If broken spontaneously at lower scales, these U(1)_B and U(1)_L symmetries provide potential avenues for preserving baryogenesis while nonetheless explaining the suppression of proton decay (without the need for R parity), as well as the smallness of right-handed neutrino Majorana masses compared to the string scale.