Limits to second-class nucleonic currents

Discussion of the effect of second-class currents in complex nuclei necessarily involves consideration of three separate contributions stemming from: (i) NNeν and NN̄eν vertices, the latter induced by exchange pions, that are characterized, respectively, by the coupling constants gT and gT′; (ii) the decay in flight of exchange mesons, predominantly ω→πeν, characterized by a decay amplitude Fω. Analysis of experimental data, following the scheme of Kubodera, Delorme and Rho, is in terms of only two parameters, ζ and λ, so that simultaneous extraction of gT,gT′ and Fω is not possible. Although experimental data do not yield significantly non-zero values for ζ and λ, the possibility therefore remains open of finite, but cancelling, second-class effects. However, the most likely source for finite gT and gT′ is vertex-renormalization by ω→πeν. Following this Ansatz, it is shown that the 90% CL upper limits to gT and gT′ are 10% of the magnitude of the natural comparator in the vector current namely gM, weak magnetism.