GLOBAL ANALYSIS OF THE TOP-QUARK COUPLINGS TO GAUGE BOSONS

We propose to probe the electroweak symmetry-breaking sector by measuring the effective couplings of the top quark to gauge bosons. Using precision CERN LEP data, we constrain the nonuniversal couplings of t-t-Z and t-b-W, parameterized by kappa(L)NC, kappa(R)NC, kappa(L)CC and kappa(R)CC, in the electroweak chiral Lagrangian framework. Different scenarios of electroweak symmetry breaking will imply different correlations among these parameters. We find that at the order of m(t)2 ln LAMBDA2, in which LAMBDA approximately 4pinu is the cutoff scale of the effective theory, kappa(L)NC is already constrained by LEP data. In models with an approximate custodial symmetry, a positive kappa(L)CC is preferred. kappa(R)CC can be constrained by studying the direct detection of the top quark at the Fermilab Tevatron and the CERN LHC. At the NLC, kappa(L)NC and kappa(R)NC can be better measured.