Neutral-current effects in a class of gauge field theories

Neutral-current couplings constitute a distinctive feature of certain models of weak interactions based on the idea of broken gauge symmetry. We discuss the observational implications for semileptonic processes; in particular, the relations among the inclusive (Δ S=0) reactions ν+N→ν+X, ν+N→μ+X, e+N→e+X. For I=0 targets, and with no further dynamical assumptions, we find the theoretical bound $\frac{{\sigma }^{(\nu \to \nu )}}{{\sigma }^{(\nu \to \mu )}}\gtrsim 0.14$ for neutrino energies above a few GeV. Additional theoretical input increases this lower bound to 0.24.