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

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.