Implications of the recent CERN LEP data on nonuniversal interactions with the precision electroweak tests

Abstract

We explore the nonuniversal interaction effects in terms of the precision variables epsilons with the recent LEP data reported by the Electroweak Working Group. The epsilon variables with the nonuniversal interactions are calculated and constrained by the experimental ellipses in the $ε_1$--$ε_b$, $ε_2$--$ε_b$, and $ε_3$--$ε_b$ planes. We find that the new data enables us to make a stringent test on the correction to $Z \to b \bar{b}$ vertex. The $ε_b$ variable is sensitive to the $Z b \bar b$ couplings and thus plays a major role to give constraints on the nonuniversal interaction effects. Upon imposing the new data on $ε_b$, we have the allowed range of the model parameter $κ_L = 0.0063 \pm 0.0030$ at 1-$σ$ level with $m_t = 175$ GeV. Along with the minimal contact term, we predict the new physics scale $Λ\sim$ 1.6 TeV. By combining the experimental results from all planes we obtain the allowed range of $κ_L$ : $0.003 < κ_L < 0.010$ at 95 % C.L..