Abstract
The effective potential of the scalar field in the SU(5) model has extrema with symmetry:SU(5), SU(4)×U(1), SU(3)×SU(2)×U(1), SU(3)×[U(1)]2, [SU(2)]2×[U(1)]2. In our recent paper it was shown that the SU(4)×U(1) phase as well as SU(3)×SU(2)×U(1) phase were stable at the nonzero temperature in a vast region of parameters. In the present paper it is found that the [SU(2)]2×[U(1)]2 symmetric vacuum is unstable and the SU(3)×[U(1)]2 symmetric vacuum can be metastable in the certain interval of the temperature. Domains of the three phases:SU(4)×U(1), SU(3)×SU(2)×U(1), SU(3)×[U(1)]2-could co-exist in the early. Universe. © 1982 Springer-Verlag.