Minimal left-right symmetry and SO(10) grand unification using LEP coupling constant measurements

Abstract

We consider embedding the standard model in a minimal left-right symmetric model. The left-right symmetry breaking is characterised by a scale M R, and accordingly the running of the couplings is modified above M R. This model can in turn be embedded in SO(10) grand unification, if the couplings evolve to a single unification point. Neglecting threshold effects, we find that this will occur for M R=10 10.44±0.33 GeV. The corresponding scale of unification is found to be M X=10 15.20 ±0.25GeV, which is not in conflict with the proton lifetime bound.