Pati–Salam model

In physics, the Pati–Salam model is a Partial Unification Theory proposed in 1974 by nobel laureate Abdus Salam and Jogesh Pati. The unification is based on there being four quark color charges, dubbed red, green, blue and violet (or lilac), instead of the conventional three, with the new "violet" quark being identified with the leptons. The model also has Left–right symmetry and predicts the existence of a high energy right handed weak interaction with heavy W' and Z' bosons.

Originally the fourth color was labelled "lilac" to alliterate with "lepton". Pati–Salam is a mainstream theory and a viable alternative to the Georgi–Glashow $SU(5)$ unification. It can be embedded within an $SO(10)$ unification model (as can $SU(5)$ ).

The Pati–Salam model states that the gauge group is either $SU(4) \times SU(2) L \times SU(2) R$ or $(SU(4) \times SU(2) L \times SU(2) R)/ Z 2$ and the fermions form three families, each consisting of the representations $(4, 2, 1)$ and $(4, 1, 2)$ . This needs some explanation. The center of $SU(4) \times SU(2) L \times SU(2) R$ is $Z 4 \times Z 2L \times Z 2R$ . The $Z 2$ in the quotient refers to the two element subgroup generated by the element of the center corresponding to the two element of $Z 4$ and the 1 elements of $Z 2L$ and $Z 2R$ . This includes the right-handed neutrino, which is now likely believed to exist. See neutrino oscillations. There is also a $(4, 1, 2)$ and/or a $(4, 1, 2)$ scalar field called the Higgs field which acquires a VEV. This results in a spontaneous symmetry breaking from $SU(4) \times SU(2) L \times SU(2) R$ to $SU(3) \times SU(2) \times U(1) Y)/ Z 3$ or from $(SU(4) \times SU(2) L \times SU(2) R)/ Z 2$ to $(SU(3) \times SU(2) \times U(1) Y)/ Z 6$ and also,

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