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, parametrized by ${\mathrm{\kappa }}_{\mathit{L}}^{\mathrm{NC}}$, ${\mathrm{\kappa }}_{\mathit{R}}^{\mathrm{NC}}$, ${\mathrm{\kappa }}_{\mathit{L}}^{\mathrm{CC}}$, and ${\mathrm{\kappa }}_{\mathit{R}}^{\mathrm{CC}}$, 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 ${\mathit{m}}_{\mathit{t}}^2$ln${\mathrm{\Lambda }}^2$, in which Λ∼4πv is the cutoff scale of the effective theory, ${\mathrm{\kappa }}_{\mathit{L}}^{\mathrm{NC}}$ is already constrained by LEP data. In models with an approximate custodial symmetry, a positive ${\mathrm{\kappa }}_{\mathit{L}}^{\mathrm{CC}}$ is preferred. ${\mathrm{\kappa }}_{\mathit{R}}^{\mathrm{CC}}$ can be constrained by studying the direct detection of the top quark at the Fermilab Tevatron and the CERN LHC. At the NLC, ${\mathrm{\kappa }}_{\mathit{L}}^{\mathrm{NC}}$ and ${\mathrm{\kappa }}_{\mathit{R}}^{\mathrm{NC}}$ can be better measured.