Limits on Anomalous Top Couplings from Z Pole Physics

We obtain constraints on possible anomalous interactions of the top quark with the electroweak vector bosons arising from the precision measurements at the $Z$ pole. In the framework of $SU(2)_L \otimes U(1)_Y$ chiral Lagrangians, we examine all effective CP--conserving operators of dimension five which induce scalar and tensor 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 shows that operators which break the $SU(2)_C$ custodial symmetry or modify the $Z b \bar{b}$ vertex are more strongly bounded.