Z′-bosons in supersymmetric E6 models confront electroweak data

Abstract

We study constraints on additional Z′-bosons predicted in the supersymmetric (SUSY) E 6 models by using the updated results of electroweak experiments — Z-pole experiments, m w measurements and low-energy neutral current (LENC) experiments. We find that the effects of Z- Z′ mixing are parametrized by (i) a tree-level contribution to the T-parameter, (ii) the effective Z- Z′ mass mixing angle ξ . n addition, the effect of the exchange of the heavier mass eigenstate Z 2 in the LENC processes is parametrized by (iii) a contact term g E 2/ c χ 2 m Z 2 2. We give the theoretical predictions for the observables in the electroweak experiments together with the standard model radiative corrections. Constraints on T new and ξ from the Z-pole and m w experiments and those on g E 2/ c χ 2 m Z 2 2 from the LENC experiments are separately shown. Impacts of the kinetic mixing between the U(1) y and U(1)′ gauge bosons on the χ 2-analysis are studied. We show the 95% CL lower mass limit of Z 2 as a function of the effective Z- Z′ mixing parameter ζ, a combination of the mass and kinetic mixings. A theoretical prediction on ζ and g E is given for the χ-, ψ-, η- and ν-models by assuming the minimal particle content of the SUSY E 6 models. In a certain region of the parameter space, the Z 2-boson mass in the detectable range of LHC is still allowed.