LIMITS ON ANOMALOUS TOP COUPLINGS FROM Z-POLE PHYSICS

We obtain constraints on possible anomalous interactions of the top qu ark with the electroweak vector bosons arising from the precision meas urements at the Z pole. In the framework of SU(2)(L) x U(1)(Y) chiral Lagrangians, we examine all effective CP-conserving operators of dimen sion five which induce fermionic currents involving the top quark. We constrain the magnitudes of these anomalous interactions by evaluating their one-loop contributions to the Z pole physics. Our analysis show s that the operators that contribute to the LEP observables get bounds close to the theoretical expectation for their anomalous couplings. W e also show that those which break the SU(2), custodial symmetry are m ore strongly bounded. (C) 1997 Elsevier Science B.V.