LEPTONIC FLAVOR VIOLATIONS IN THE PRESENCE OF AN EXTRA-Z

Gauged extensions [SU(2)L x U(1)Y x U(1)X] of the standard SU(2)L x U( 1)Y model obtained without extending the fermion content of the model are studied. Models that are possible when U(1)X is identified with so me combination of the family lepton numbers are systematically classif ied. Most of these contain flavor violations in the leptonic sector. T hese flavor violations are correlated to the mixing of the U(1)X gauge boson Z' with the ordinary Z in the models considered here. Detailed phenomenological implications of a typical model are discussed. Constr aints on the Z' mass and the Z-Z' mixing following from (i) the observ ations at CERN LEP, (ii) rare processes such as Z --> etau, and (iii) flavor-violating tau decays are presented. It is found that the constr aints coming from the LEP allow rare processes such as tau --> eee at the level of the present limits on its branching ratio. Thus the futur e search could either improve on the existing LEP limits or would find such flavor-violating decays.