Constraint on additional neutral gauge bosons from electroweak radiative corrections.

Abstract

Quantum loop corrections to the quark mixing matrix resulting from additional neutral gauge bosons are computed. Agreement between the finding \ensuremath{\Vert}${\mathit{V}}_{\mathrm{ud}}$${\mathrm{\ensuremath{\Vert}}}^{2}$+\ensuremath{\Vert}${\mathit{V}}_{\mathrm{us}}$${\mathrm{\ensuremath{\Vert}}}^{2}$+\ensuremath{\Vert}${\mathit{V}}_{\mathrm{ub}}^{2}$=0.9984\ifmmode\pm\else\textpm\fi{}0.0021 and the unitarity value of 1 is used to provide a generic bound on masses and couplings of such bosons. For grand unified models of the type SO(100\ensuremath{\rightarrow}SU(3${)}_{\mathit{C}}$\ifmmode\times\else\texttimes\fi{}SU(2${)}_{\mathit{L}}$\ifmmode\times\else\texttimes\fi{}U(1)\ensuremath{\approxeq}U(1${)}_{\mathit{X}}$, \ensuremath{\gtrsim}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 ${\mathrm{E}}_{6}$\ensuremath{\rightarrow}SU(3${)}_{\mathrm{C}}$\ifmmode\times\else\texttimes\fi{}SU(2${)}_{\mathrm{L}}$\ifmmode\times\else\texttimes\fi{}U(1) \ifmmode\times\else\texttimes\fi{}U(1${)}_{\mathrm{\ensuremath{\eta}}}$\ifmmode\times\else\texttimes\fi{}U(1${)}_{\mathrm{\ensuremath{\eta}}\mathcal{'}}$ with , we obtain the bound \ensuremath{\ge}254 GeV at 90% C.L.