Can very light neutral vector bosons exist

Models which unify strong, electromagnetic, and weak interactions contain many neutral gauge fields. A generalization of the Pati-Salam model with fractional-charge quarks is used as an example to investigate whether all gauge fields, except those coupled to the SU(2) x U(1) subgroup of Weinberg-Salam, must develop large masses and become unobservable. The possible existence of a neutral boson with a mass much smaller than that of W/sup plus-or-minus/ is considered. Constraints from known properties of neutral currents together with the assumption of an explicit symmetry-breaking mechanism produce a model with two neutral vector bosons, neither of which has the Weinberg-Salam structure. One particle is very light and decoupled from left-handed neutrinos, and the other is heavy and responsible for observed neutral-current interactions. A brief comparison with experimental data does not exclude this model. The existence of a very light, neutral, purely charm-changing neutral vector boson is considered