Prospects for a second neutral vector boson at low mass in SO(10)

Abstract

Symmetries $\mathrm{SU}{(3)}_{c}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ arising from a specific class of models involving the spontaneous breakdown of SO(10) are considered. In these, two neutral vector bosons ${Z}_{1}$ and ${Z}_{2}$ arise. The ${Z}_{1}$ is expected to be very similar to the ${Z}_{0}$ of the standard $\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ model. The most restrictive constraints, arising from the Novosibirsk experiment on parity violation in atomic bismuth, imply $0.98\ensuremath{\le}\frac{M({Z}_{1})}{M({Z}_{0})}\ensuremath{\le}1$. The ${Z}_{2}$ can be as light as $(2.5\ensuremath{-}3)M({Z}_{0})$. Its effects in neutral-current interactions, couplings, and production mechanisms are examined.