Neutral-current constraint and gauge models

The experimental observation R^νR^ν<σcc^νσcc^ν, i.e., σnc^ν>σnc^ν, where σcc,nc^ν(ν) are the ν-(ν-) induced charged- and neutral-current inclusive cross sections on an isospin-0 nucleon and ${R}^{{ν}({{ν}})} = {{{σ}}nc^{{ν}({{ν}})}}{{{σ}}cc^{{ν}({{ν}})}}, provides a constraint on the possible quark representations among various SU(2) × U(1) gauge models. We have examined the energy dependence of both{ν}{-}({{ν}}{-})$ induced charged- and neutral-current processes in the models which respect the constraint. Some of the models contain one or a few heavy quarks with an exotic charge of $Q = 5/3 and/orh {{-}4}{3}$.