Dimension-5 baryon-number violation in low-scale Pati-Salam

TL;DR

This paper investigates how low-scale Pati-Salam models can generate dangerous dimension-5 operators leading to rapid nucleon decay, constraining the symmetry breaking scale to be above approximately 10^8 GeV.

Contribution

It demonstrates that low-scale Pati-Salam models inherently produce dimension-5 operators causing nucleon decay, imposing significant bounds on the model's breaking scale.

Findings

Dimension-5 operators induce rapid nucleon decay.

Constraints suggest the breaking scale must be above ~10^8 GeV.

Embedding into SO(10) further lowers the suppression scale.

Abstract

The gauge bosons of Pati-Salam do not mediate proton decay at the renormalisable level, and for this reason it is possible to construct scenarios in which $SU(4) \otimes SU(2)_{R}$ is broken at relatively low scales. In this Letter we show that such low-scale models generate dimension-5 operators that can give rise to nucleon decays at unacceptably large rates, even if the operators are suppressed by the Planck scale. We find an interesting complementarity between the nucleon-decay limits and the usual meson-decay constraints. Furthermore, we argue that these operators are generically present when the model is embedded into $SO(10)$, lowering the suppression scale. Under reasonable assumptions, the lower limit on the breaking scale can be constrained to be as high as $\mathcal{O}(10^{8})$ GeV.