Bounds on the mass ofWRand theWL−WRmixing angleζin generalSU(2)L×SU(2)R×U(1)models

Abstract

We consider the phenomenological constraints on the mass ${M}_{R}$ and the ${W}_{L}\ensuremath{-}{W}_{R}$ mixing angle $\ensuremath{\zeta}$ in a very general class of $\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(2)}_{R}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ models. In particular, almost no model-dependent assumptions are made concerning left-right symmetry or the Higgs structure of the theory, which means that ${U}^{R}$, the mixing matrix for right-handed quarks, is unrelated to the left-handed Cabibbo-Kobayashi-Maskawa matrix ${U}^{L}$. 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 ${K}_{L}\ensuremath{-}{K}_{S}$ mass difference, ${B}_{d}{\overline{B}}_{d}$ 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 ${M}_{R}$ are considerably weaker than for the special case of manifest or pseudomanifest left-right symmetry (${M}_{R}>1.4$ TeV). In fact, if extreme fine-tuning is allowed the ${W}_{R}$ could be as light as the ordinary ${W}_{L}$. However, with reasonable restrictions on fine-tuning one obtains ${M}_{R}>300$ GeV for ${g}_{R}={g}_{L}$, with more stringent limits holding for most of parameter space. If $\mathrm{CP}$-violating phases in ${U}^{R}$ are small the limit on mixing ($|\ensuremath{\zeta}|<0.0025$ for ${g}_{R}={g}_{L}$) is almost as stringent as for the case of left-right symmetry. For large phases $|\ensuremath{\zeta}|$ could be as large as \ensuremath{\sim}0.013.