Constraint on additional neutral gauge bosons from electroweak radiative corrections

Quantum loop corrections to the quark mixing matrix resulting from additional neutral gauge bosons are computed. Agreement between the finding ‖${\mathit{V}}_{\mathrm{ud}}$ ${\mathrm{\Vert }}^2$+‖${\mathit{V}}_{\mathrm{us}}$ ${\mathrm{\Vert }}^2$+‖${\mathit{V}}_{\mathrm{ub}}^2$=0.9984±0.0021 and the unitarity value of 1 is used to provide a generic bound on masses and couplings of such bosons. For grand unified models of the type SO(100→SU(3${)}_{\mathit{C}}$×SU(2${)}_{\mathit{L}}$×U(1)≊U(1${)}_{\mathit{X}}$, &≳266 GeV at 90% confidence limit. That bound also applies to the extra boson in some specific ${\mathrm{E}}_6$ superstring-motivated models. In the general case of ${\mathrm{E}}_6$→SU(3${)}_{\mathrm{C}}$×SU(2${)}_{\mathrm{L}}$×U(1) ×U(1${)}_{\mathrm{\eta }}$×U(1${)}_{\mathrm{\eta }\mathcal{’}}$ with &, we obtain the bound &≥254 GeV at 90% C.L.