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 ($\Delta S=0\mathrm{}$) reactions $\nu +N\to \nu +X$, $\nu +N\to \mu +X$, $e+N\to e+X$. For $I=0\mathrm{}$ 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.