A possible SU(7) grand unified model with non-standard charged quarks, lepton and low-mass magnetic monopole

A possible SU(7) grand unified model with non-standard charged quarks, lepton and low-mass magnetic monopole is proposed. In this model, the quarks and leptons of the first and the second generations are the same as in the standard GUM, but the assignment of the fermions of the third and the fourth generations is quite different from the standard GUM. Although the charge of the top quark is 2/3, the b quark Q = -1/3, the tau lepton Q = -1, there are also two kinds of quarks with Q = 5/3, -4/3 and a lepton with Q = -2. The coupling of e-νsub(e), μ-νsub(μ) and tau-μsub(tau) is V-A. We break SU(7) down to SU(3) and U(1)sub(em) in three steps. We estimate the proton decay lifetime tsub(p) and the mass of the magnetic monopole Msub(m). In the experimentally plausible ranges of the weak mixing angle sin2thetasub(w)(Msub(w)) and the strong-coupling constant αsub(s)(Msub(w)), 0.18 <= sin2thetasub(w)(Msub(w)) <= 0.22, 0.15 <= αsub(s)(Msub(w)) <= 0.24, respectively, tsub(p) > 1030 yr, which sensitively depends on the mass scale of the grand unified point, and Msub(m) approx. equal to 106 GeV, which is almost independent of sin2thetasub(w)(Msub(w)) and αsub(s)(Msub(w)) and consistent with the big-bang theory of the universe. (orig.)