A 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 LEP data, we constrain the non--universal 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 found that at the order of ${m_t}^{2}\log {\Lambda}^2$, in which $\Lambda \sim 4 \pi v$ is the cut--off 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. $\kappa_{L}^{CC}$ can be constrained by studying the direct detection of the top quark at the Tevatron and the LHC. At the NLC, $\kappa_{L}^{NC}$ and $\kappa_{R}^{NC}$ can be better measured.