Lepton Parity in Supersymmetric Flavor Models

TL;DR

This paper explores supersymmetric models without R-parity, where an exact lepton parity emerges from a broken horizontal U(1) symmetry, naturally suppressing proton decay and neutrino mass contributions.

Contribution

It introduces a novel framework where lepton parity arises as an exact residual symmetry from a broken U(1), explaining neutrino hierarchies and suppressing baryon number violation.

Findings

Lepton parity is an exact residual symmetry in the model.

The model naturally suppresses proton decay and neutron oscillations.

Neutrino parameters are consistent with observed hierarchies.

Abstract

We investigate supersymmetric models where neither R-parity nor lepton number nor baryon number is imposed. The full high energy theory has an exact horizontal U(1) symmetry that is spontaneously broken. Quarks and Higgs fields carry integer horizontal charges but leptons carry half integer charges. Consequently, the effective low energy theory has two special features: a U(1) symmetry that is explicitly broken by a small parameter, leading to selection rules, and an exact residual Z_2 symmetry, that is lepton parity. As concerns neutrino parameters, the Z_2 symmetry forbids contributions from R_p-violating couplings and the U(1) symmetry induces the required hierarchy. As concerns baryon number violation, the Z_2 symmetry forbids proton decay and the U(1) symmetry provides sufficient suppression of double nucleon decay and of neutron - antineutron oscillations.