We consider the phenomenological constraints on the mass MR and the WL-WR mixing angle in a very general class of SU(2)L×SU(2)R×U(1) models. In particular, almost no model-dependent assumptions are made concerning left-right symmetry or the Higgs structure of the theory, which means that UR, the mixing matrix for right-handed quarks, is unrelated to the left-handed Cabibbo-Kobayashi-Maskawa matrix UL. We consider a number of possibilities for the neutrinos occurring in right-handed currents, including (a) heavy Majorana neutrinos, (b) heavy Dirac neutrinos, (c) intermediate-mass (10-100 MeV) neutrinos, and (d) light neutrinos (e.g., the Dirac partners of the ordinary left-handed neutrinos). For each case we utilize relevant constraints from the KL-KS mass difference, BdB»d oscillations, the b semileptonic branching ratio and decay rate, neutrinoless double-beta decay, theoretical relations between mass and mixing, universality, nonleptonic kaon decays, muon decay, and astrophysical constraints from nucleosynthesis and SN 1987A. As is to be expected the limits on MR are considerably weaker than for the special case of manifest or pseudomanifest left-right symmetry (MR>1.4 TeV). In fact, if extreme fine-tuning is allowed the WR could be as light as the ordinary WL. However, with reasonable restrictions on fine-tuning one obtains MR>300 GeV for gR=gL, with more stringent limits holding for most of parameter space. If CP-violating phases in UR are small the limit on mixing (||<0.0025 for gR=gL) is almost as stringent as for the case of left-right symmetry. For large phases || could be as large as 0.013.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)