1. Particle Data Group collaboration, J. Beringer et al., Review of Particle Physics (RPP), Phys. Rev. D 86 (2012) 010001 [ INSPIRE ].
2. R.N. Mohapatra, Unification and supersymmetry. The frontiers of quark-lepton physics, Springer, New York, U.S.A. (2003).
3. J.L. Hewett and T.G. Rizzo, Low-Energy Phenomenology of Superstring Inspired E 6 Models, Phys. Rept. 183 (1989) 193 [ INSPIRE ].
4. P. Langacker and S.U. Sankar, Bounds on the Mass of W R and the W L − W R Mixing Angle ξ in General SU(2) L × SU(2) R × U(1) Models, Phys. Rev. D 40 (1989) 1569 [ INSPIRE ].
5. V.D. Barger, K. Whisnant and W.-Y. Keung, Gauge model with heavy weak bosons and small additional neutral-current interaction proportional to charge squared, Phys. Rev. D 25 (1982) 291(R) [ INSPIRE ].PhysRevD.25.291