Magnetic Monopoles and Exotic States in $SU(4)_c \times SU(2)_L \times SU(2)_R$

Abstract

In the Pati-Salam gauge symmetry $SU(4)_c \times SU(2)_L \times SU(2)_R$ (4-2-2, for short), the observed quarks and leptons of each family reside in the bi-fundamental representations $(4,2,1)$ and $({\bar 4},1,2)$. There exist, however, the fundamental representations $(4,1,1)$, $(1,2,1)$ and $(1,1,2)$ and their hermitian conjugates, which show the presence, in principle, of yet to be discovered color triplets that carry electric charge $\pm{e/6}$, and color singlet particles with charges of $\pm{e/2}$. These Standard Model charges are in full accord with the fact that the 4-2-2 model predicts the presence of a topologically stable finite energy magnetic monopole that carries two quanta of Dirac magnetic charge, i.e., $4 \pi/e$, as well as color magnetic charge that is screened beyond the quark confinement scale. The 4-2-2 model therefore predicts the existence of exotic baryons, mesons and leptons that carry fractional ($\pm{e/2}$) electric charges. Since their origin lies in the fundamental representations of 4-2-2, these exotic particles may turn out to be relatively light, in the TeV mass range or so. The 4-2-2 magnetic monopole mass depends on the 4-2-2 symmetry breaking scale which may be as low as a few TeV.