Low - Scale SU ( 4 ) W Unification

We embed the minimal left-right model SU(2)L × SU(2)R × U(1)B−L into an SU(4)W gauge group, and break the unified group via five-dimensional S /(Z2 × Z2) orbifolding. Leptons are fitted into SU(4)W multiplets and located on a symmetry preserving O brane, while quarks are placed onto an O brane where the symmetry is broken. This approach predicts sin θW = 0.25 for the weak mixing angle at tree level and leads to a rather low unification scale of order 3 × 102 TeV with supersymmetry, or as low as several TeV in the non-supersymmetric case. Another symmetry breaking chain with the low-energy gauge group SU(2)L × U(1)3R × U(1)B−L can also give rise to a weak mixing angle sin θW = 0.25 at tree level after gauge symmetry breaking by orbifolding. Such theories with low-scale unification have interesting phenomenological consequences.