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 $\epsilon_1$--$\epsilon_b$, $\epsilon_2$--$\epsilon_b$, and $\epsilon_3$--$\epsilon_b$ 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 $\epsilon_b$ 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 $\epsilon_b$, we have the allowed range of the model parameter $\kappa_L = 0.0063 \pm 0.0030$ at 1-$\sigma$ level with $m_t = 175$ GeV. Along with the minimal contact term, we predict the new physics scale $\Lambda \sim$ 1.6 TeV. By combining the experimental results from all planes we obtain the allowed range of $\kappa_L$ : $0.003 < \kappa_L < 0.010$ at 95 % C.L..