V + A currents coupling old quarks to new

We study some consequences of the existence of new quark flavors. We do this in the framework of gauge models, with V + A couplings of old to new quarks and allowing for mixing of different SU(2) × U(1) representations. High-energy neutrino and e⁺e^- experiments may suggest (and can prove) the existence of new flavors. Low-energy neutrino neutral current experiments are sensitive to the way new quarks and their currents are added to the standard Weinberg-Salam model. We show that if new quarks with weak couplings to old u, d quarks are needed at all, low-energy neutral current data may favor a new class of models having non-diagonal neutral currents. However, the special case of a maximal charm-changing neutral current appears to be excluded by high-energy experiments.