Abstract

The observed baryon asymmetry (BAU) of the universe puts strong constraints on any (B - L)-violating interaction. An observation of a (B - L)-violating nucleon decay channel would therefore have profound implications for our understanding of the BAU. Here we point out that the observation of the final state with a kaon and a charged lepton in a future nucleon decay experiment would hint at (B - L) violation even if the charge of the lepton is not determined experimentally. In SMEFT, this follows from the fact that n -> K + & ell; - arises already at dimension seven, while the (B - L)-conserving decay n -> K - & ell; + requires dimension-ten operators that, in addition, would be accompanied by lower-dimensional (B + L)-violating decay modes. An observation of n -> K & ell; in the absence of other modes such as p -> pi 0 & ell; +, would then strongly suggest that (B - L) is violated.