On B and L violation in the laboratory in the light of cosmological and astrophysical constraints

We have pointed out previously that the survival of a cosmological baryon asymmetry despite strong non-perturbative electroweak interactions puts severe constraints on extensions of the Standard Model that violate baryon number B and/or lepton number L. After reviewing this argument including numerical factors, and implementing astrophysical constraints, in this paper we discuss the prospects for observing B and/or L violation in laboratory experiments. Modulo loopholes that we mention, we find that even if R parity is violated, the lifetime of the lightest supersymmetric particle must be so long that its decays could not be observed in accelerator experiments, and the L-violating Z decays would have unobservably small branching ratios. The only novel signature for accelerator experiments that survives our analysis is a small window for the lightest supersymmetric particle to be strongly-interacting or charged, with a lifetime that is short on a cosmological time-scale but long enough to appear stable in accelerator experiments. We also find that even if Delta B = 2 interactions exist, the rates they yield for n-(n) over bar oscillations and N-N annihilations in nuclei must be unobservably small.