SO(10) FOR GRAND UNIFICATION?

Abstract

In this brief review, we present the arguments both theoretical and experimental in favor of the simple group SO(10) as the first approximation towards grand unification. The physical phenomena of the solar neutrino problem which motivate existence of neutrino mass, the recent LEP data which rule out the simple SU(5) (and perhaps supersymmetric SU(5) if tied also to the solar neutrino problem) model for which vanishing neutrino masses would be logical, coupled with attractive features like accommodating the invisible axion and a τ neutrino mass acceptable to cosmology, converge towards a two-step SO(10) model with intermediate mass scale of order 1011 GeV . We comment on the status of a second Z′ in a model of the spontaneous breakdown of SO(10) which is particularly conservative in that very little of the standard picture is altered.