How long could we live?

We investigate model independent upper bounds on total proton lifetime in the context of grand unified theories with the Standard Model matter content. We find them to be tau(p) <= 1.5(-0.3)(+0.5) x 10(39) alpha(2)(GUT)/ (M-X/10(16) GeV)(4) (0.003 GeV3 /alpha)(2) years and tau(p) <= 7.1(-0.0)(+0.0) x 10(36) alpha(2)(GUT)/ (M-X/10(16) GeV)(4) (.003 GeV3/alpha)(2) years in the Majorana and Dirac neutrino case, respectively. These bounds, in conjunction with experimental limits, put lower limit on the mass M-X of gauge bosons responsible for the proton and bound-neutron decay processes. For central values of relevant input parameters we obtain M-X >= 4.3 x 10(14) root alpha GUT GeV. Our result implies that a large class of non-supersymmetric grand unified models, with typical values alpha GUT similar to 1/39, still satisfies experimental constraints on proton lifetime. Our result is independent on any CP violating phase and the only significant source of uncertainty is associated with imprecise knowledge of alpha-the nucleon decay matrix element. (c) 2005 Published by Elsevier B.V.