Flavor unity in SU(7): Low-mass magnetic monopole, doubly charged lepton, andQ=53,−43quarks

A specific flavor unification is suggested in the SU(7) gauge group. This model can be trivially extended to O(14). A global symmetry $\Gamma$ forbids mixings of the $b$ ($Q=-\frac{1}{3}$) quark with the $d$ and $s$ quarks, and of the $t$ ($Q=\frac{2}{3}$) quark with the $u$ and $c$ quarks. Since the $b$ and $t$ quarks carry different $\Gamma$ quantum numbers, they do not belong to the same $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L$ doublet. A mechanism for the $\Gamma$-symmetry violation is suggested, which allows $c-t$ mixing without $b$-quark mixing. There are unconventionally charged light (masses ≲ 300 GeV) fermions: a doubly charged lepton $T^{--}$, a $Q=-\frac{4}{3}$ quark $x$, and a $Q=\frac{5}{3}$ quark $y$. The bare value of the Weinberg angle ${{sin}^2\theta }_W^0=\frac{3}{20}$ is renormalized to the low-energy value by introducing an intermediate mass scale $M_1$. A topologically stable magnetic monopole is light ($\mathrm{mass}\approx \frac{M_1}{\alpha }$) and hence there does not exist a conflict arising from the grand unified theories and the hot-big-bang cosmology.