Heavy Majorana leptons and cosmological baryon excess

Cosmological baryon excess is used to probe how the left-right symmetry should be broken in a basically symmetric grand unified theory. In the SO(10) model, the contribution from an intermediate state containing the chiral partner of a light ordinary neutrino cancels much of the usual baryon excess produced by a heavy-Higgs-boson decay unless the partner's mass is 1010 GeV. A mechanism of soft CP violation is also mentioned.