Proton stability from a fourth family

TL;DR

This paper demonstrates that adding a fourth family of fermions naturally enforces baryon number conservation and R-parity in supersymmetric models, potentially explaining proton stability without new flavor structures.

Contribution

It shows that a fourth fermion family with three colors inherently conserves baryon number and R-parity, providing a minimalistic approach to proton stability.

Findings

Baryon number is conserved up to negligible high-dimension operators with four generations.

Supersymmetric models with a fourth family naturally enforce R-parity.

Minimality conditions prevent dangerous baryon- or lepton-number violating operators.

Abstract

The possibility to violate baryon or lepton number without introducing any new flavor structures, beyond those needed to account for the known fermion masses and mixings, is analyzed. With four generations, but only three colors, this minimality requirement is shown to lead to baryon number conservation, up to negligible dimension-18 operators. In a supersymmetric context, this same minimality principle allows only superpotential terms with an even number of flavored superfields, hence effectively enforces R-parity both within the MSSM and in a GUT context.