Improved lower bounds on partial lifetimes for nucleon decay modes

In the framework of a baryon-number-violating effective Lagrangian, we calculate improved lower bounds on partial lifetimes for proton and bound neutron decays, including p→+′+′-n→ν+′-, p→+νν, and n→ννν, where and ′ denote e or μ, with both =′ and ≠′ cases. Our lower bounds are substantially stronger than the corresponding lower bounds from direct experimental searches. We also present lower bounds on (τ/B)p→+γ, (τ/B)n→νγ, (τ/B)p→+γγ, and (τ/B)n→νγγ. Our method relies on relating the rates for these decay modes to the rates for decay modes of the form p→+M and n→νM, where M is a pseudoscalar or vector meson, and then using the experimental lower bounds on the partial lifetimes for these latter decays.