Nucleon decays into three leptons: Noncontact contributions

Abstract

We investigate baryon number violating (BNV) nucleon decays into three leptons from noncontact contributions that are induced by dimension-6 (dim-6) BNV operators in low-energy effective field theory (LEFT) with an exchange of a baryon, meson, lepton, or photon field. We systematically classify all these processes that change lepton flavor by one unit and formulate their decay widths in terms of the dim-6 LEFT Wilson coefficients. By applying constraints on these Wilson coefficients derived from current experimental limits on BNV two-body nucleon decays, we obtain stringent bounds on the rates of these triple-lepton modes. These bounds vary significantly from one dim-6 operator to another under consideration. Our results for the $\Delta(B-L)=0$ modes differ by several orders of magnitude from previous phase-space estimates in the literature, thereby providing a more reliable assessment of their potential occurrence. In addition, we provide improved bounds on $\Delta(B+L)=0$ modes compared to the existing experimental limits.