Low-Scale SU(4)W Unification
Abstract
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 S1/(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 2θW=0.25 for the weak mixing angle at tree level and leads to a rather low weakly (strongly) coupled unification scale of order 3*102 TeV (several 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 2θW=0.25 at tree level after gauge symmetry breaking by orbifolding. Such theories with low-scale unification have interesting phenomenological consequences.