Aspects of the grand unification of strong,weak and electromagnetic interactions

We study issues arising in attempts to unify strong and other elementary particle interactions. The proton lifetime is estimated in theories with second-order baryon number violation, and found to be O(10³–10⁴) longer than naive dimensional counting suggested. The renormalization of quark and lepton masses below the grand unification mass is considered in some detail. Application is made to the SU(5) model of Georgi and Glashow, and we find strange and bottom quark masses:

$\text{m}{}_{\mathrm{<mtext>s</mtext>}}\text{≈ 0.4–0.5}\text{GeV}\text{, m}{}_{\mathrm{<mtext>b</mtext>}}\text{≈ 4.8–5.6}\text{GeV}$

. Inputs are the values of the strong interactions coupling constant favoured by electroproduction and charmonium analyses, and the observed muon and heavy lepton (τ) masses. These estimates are substantially increased if there are more than six flavours of quark. Symmetry breaking in the SU(5) model is studied, including radiative corrections to the effective Higgs potential.     

SuperB production,matter stability and gauge hierarchy in SUSY GUTs

We analyze the connections between the problems of the cosmological baryon asymmetry (CBA), matter stability and mass hierarchy in supersymmetric Grand Unified models. We show that the typical delay of the phase transition in supersymmetric theories as well as a natural solution to the triplet-doublet Higgs hierarchy problem imply baryon production after the Grand Unification phase transition which in a wide class of SUSY GUTs takes place atT～10⁹–10¹⁰ GeV. Light Higgs colour triplets as a means of producing the CBA are discussed in detail. An alternative mechanism involving a singlet superfield is proposed leading to striking consequences in proton decay with the appearance of (B+L) conserving modes with a muon and a kaon in the final state:n→μ^? K ⁺,p μ ^2212;π⁺ K ⁺ and a lifetime of 10³¹ years.