Dimension-five baryon-number violation in low-scale Pati-Salam models

The gauge bosons of the Pati-Salam model do not mediate proton decay at the renormalizable level, and for this reason it is possible to construct scenarios in which SU(4) (R) SU(2)R is broken at relatively low scales. In this paper we show that such low-scale models generate dimension-five 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 O(108) GeV.

Automated summary

The gauge bosons of the Pati-Salam model cannot mediate proton decay at the renormalizable level, allowing for the possibility of breaking SU(4) (R) SU(2)R at relatively low scales. However, low-scale models in this paper generate dimension-five operators that can cause nucleon decays with unacceptably high rates, even if the operators are suppressed by the Planck scale. Interestingly, there is a complementarity between nucleon-decay limits and meson-decay constraints, and embedding the model into SO(10) leads to the presence of these operators and a lower suppression scale. Under reasonable assumptions, the lower limit on the breaking scale can be constrained to be as high as O(108) GeV.