Higgs Bosons and Matter - Antimatter Oscillations in {GUTs}

The presence of Higgs bosons of diquark and dilepton types at intermediate mass scales in GUTs is analysed in connection with the possible generation of neutron-antineutron and hydrogen-antihydrogen oscillations. Their renormalization effects on the calculation of the parameters sin2θw and mb/mτ are investigated in SU(5) and in an SO(10) version with a left-right symmetric breaking chain. In correspondence with suitable combination of higgses, we find solutions in SU(5) for nG=3 and reasonable values of sin2θw, mb/mτ and proton lifetime τp, which allow detectable n-n, but undetectable H-H transitions. Solutions of this type, but with higher τp, are also found in a particular scheme of SO(10), where the intermediate mass is at the scale MR at which the left-right symmetry is broken and is of order 102×mw. This modifies then conclusions of analyses of SO(10) models, where either no diquarks and dileptons or only a specific set of them are taken into account. An extension of our analysis to supersymmetric versions of SU(5) and SO(10) does not produce acceptable solutions.