Right-handed Charged Gauge Boson Research Articles

Unraveling the left-right mixing using 0νββ decay and collider probes

In the context of the minimal left-right symmetric model, we study the interplay between current and future neutrinoless double beta ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay experiments, long-lived particle searches at the LHC main detectors ATLAS/CMS, and the proposed far detector MATHUSLA. The heavy Majorana neutrino can be produced in association with an electron from the decay of $W$ boson for a nonzero left-right mixing and subsequently decays into another electron with the same charge and jets. Owing to the suppression of large right-handed charged gauge boson ${W}_{R}$ mass, the heavy neutrinos could be long-lived. We show that long-lived particle (LLP) searches for heavy Majorana neutrinos in the same-sign dilepton channel at the LHC can be used to extend ${W}_{R}$ boson mass reach relative to the reach of the Keung-Senjanovic (KS) process. Finally, we show that sensitivities of LLP searches at the high-luminosity LHC with main detectors ATLAS/CMS are competitive with those of future $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay searches.

Neutrinoless double beta decay in the left-right symmetric models for linear seesaw

In a class of left-right symmetric models for linear seesaw, a neutrinoless double beta decay induced by the left- and right-handed charged currents together will only depend on the breaking details of left-right and electroweak symmetries. This neutrinoless double beta decay can reach the experimental sensitivities if the right-handed charged gauge boson is below the 100 TeV scale.

Right-handed quark mixing in left-right symmetric theory.

We give exact formulas for the right-handed analog of the Cabibbo-Kobayashi-Maskawa (CKM) matrix in the minimal left-right symmetric theory, for the case when the left-right symmetry is generalized parity as in the original version of the theory. We derive its explicit form and give a physical reason for the known and surprising fact that the right-handed mixing angles are close to the CKM ones, in spite of the left-right symmetry being badly broken in nature. We exemplify our results on the production of the right-handed charged gauge boson and the computation of K(L)-K(S) mass difference.

Signal of right-handed charged gauge bosons at the LHC?

We point out that the recent excess observed in searches for a right-handed gauge boson W_R at CMS can be explained in a left-right symmetric model with D parity violation. In a class of SO(10) models, in which D parity is broken at a high scale, the left-right gauge symmetry breaking scale is naturally small, and at a few TeV the gauge coupling constants satisfy g_R ~ 0.6 g_L. Such models therefore predict a right-handed charged gauge boson W_R in the TeV range with a suppressed gauge coupling as compared to the usually assumed manifest left-right symmetry case g_R = g_L. The recent CMS data show excess events which are consistent with the cross section predicted in the D parity breaking model for 1.9 TeV < M_{W_R} < 2.4 TeV. If the excess is confirmed, it would in general be a direct signal of new physics beyond the Standard Model at the LHC. A TeV scale W_R would for example not only rule out SU(5) grand unified theory models. It would also imply B-L violation at the TeV scale, which would be the first evidence for baryon or lepton number violation in nature and it has strong implications on the generation of neutrino masses and the baryon asymmetry in the Universe.

Limits on the left-right symmetry scale and heavy neutrinos from early LHC data

We use the early Large Hadron Collider data to set the lower limit on the scale of Left-Right symmetry, by searching for the right-handed charged gauge boson $W_R$ via the final state with two leptons and two jets, for 33/pb integrated luminosity and 7 TeV center-of-mass energy. In the absence of a signal beyond the Standard Model background, we set the bound M_WR > 1.4 TeV at 95% C.L.. This result is obtained for a range of right-handed neutrino masses of the order of few 100 GeV, assuming no accidental cancelation in right-handed lepton mixings.

Orbifold breaking of left–right gauge symmetry

We study the five-dimensional left–right symmetric gauge theory in which the gauge symmetry is broken down through orbifold compactification to four dimensions. The right-handed charged gauge boson, W R is a Kaluza–Klein excited state in this model, and unlike the usual left–right symmetric model in four dimension, there is no mixing in the charged sector. We develop the formalism and give expressions for the gauge boson masses and mixings and their couplings to the fermions. Phenomenology of the model is briefly studied to put constraints on the right-handed gauge boson masses and the orbifold compactification scale.

WR effects on CP asymmetries in B meson decays

After we have limited elements of the right-handed CKM matrix to satisfy the bounds for CP violation epsilon_K in K meson systems, the right-handed charged current gauge boson W_R is shown to substantially affect CP asymmetries in B systems. A joint chi-squared analysis is applied to B-Bbar mixing to constrain the right-handed CKM matrix elements. In (sin(2alpha), sin(2beta)), (x_s, sin(gamma)), (rho-eta), and (x_s, sin(2phi_s)) plots in the presence of the W_R boson, we find larger allowed experimental regions that can distinguish this model from the standard model.

Anatomy of mixing-induced CP asymmetries in left–right symmetric models with spontaneous CP violation

We investigate the pattern of CP violation in K 0– K 0 ̄ , B 0 d – B 0 d ̄ and B 0 s – B 0 s ̄ mixing in a symmetrical SU(2) L ×SU(2) R ×U(1) model with spontaneous CP violation. From a set of fixed quark masses and mixings, we calculate the phases of the left and right quark mixing matrices beyond the small phase approximation and perform a careful analysis of all relevant restrictions on the model's parameters from Δm K , Δm B , ϵ, ϵ′/ ϵ and the CP asymmetry a CP in B 0 d → J/ ψK 0 S . Of 64 possible sets of phases, most are excluded because they imply opposite signs for Re ϵ and a CP. For the one remaining set, a CP is predicted to be small (⩽0.1) for the chosen input quark masses and mixings. Barring an instability with respect to these input values, the model is thus soon to be critically tested at B factories. The mass of the right-handed charged gauge boson, M 2, is restricted to be in the range 2.75 to 13 TeV, and the mass of the flavour-changing neutral Higgs bosons, M H , in 10.2 to 14.6 TeV. This means in particular that the decoupling limit M 2, M H →∞ is already excluded by experiment.

WR effects on CP angles determination at a B factory

The right-handed charged current gauge boson W R can affect significantly on the determination of the CP violation angles to be measured at B factories if the right-handed current quark mixing matrix V R is taken to a specific form to satisfy the bounds by neutral K meson system. The W R contribution can be sizable in B 0- B 0 mixing and tree level b quark decay. The deviation of the CP angles in unitarity triangle from the standard model values can be as large as −32° ∼ +19° for f 3 (γ), and 66° ∼ 115° for f 1 (β) and f 2 (α) for m t = 175 GeV.

Measurements of the antineutrino spin asymmetry in beta decay of the neutron and restrictions on the mass of a right-handed gauge boson.

We report a new measurement of the neutron antineutrino spin asymmetry coefficient {ital B} in the beta decay of polarized neutrons. Combining results of measurements of the observed asymmetry {ital PB}=0.6617{plus_minus}0.0044 with measurements of the neutron beam polarization {ital P}=(66.88{plus_minus}0.22)%, we obtain the value {ital B}=0.9894{plus_minus}0.0083. This value implies that the mass of a hypothetical right-handed charged gauge boson in the left-right symmetric model of the weak interaction is greater than 281GeV/{ital c}{sup 2} (90% C. L.). This is in agreement with restrictions from muon decay and direct searches for an additional vector boson {ital W}{prime}.

New bound on right-handed charged gauge boson mass.

Using our previous bounds on $\ensuremath{\Delta}\ensuremath{\rho}$ and the $Z\ensuremath{-}{Z}^{\ensuremath{'}}$ mixing angle ${\ensuremath{\xi}}_{N}$ in the $\mathrm{SU}{(2)}_{L}\ensuremath{\bigotimes}\mathrm{SU}{(2)}_{R}\ensuremath{\bigotimes}\mathrm{U}{(1)}_{(B\ensuremath{-}L)}$ model from the $Z$ line shape and energy-dependent forward-backward asymmetries of the 1990 data from CERN LEP, we obtain a strong lower bound \ensuremath{\sim}439 GeV at 90% C.L. on the right-handed charged gauge boson mass for ${m}_{t}=200$ GeV using commonly chosen Higgs triplets, which becomes stronger for doublet Higgs fields. It is independent of the neutrino mass or of assumptions about the right-handed quark mixing matrix. Consequences of more exotic Higgs multiplets are also discussed.

TheK L-K S mass difference in left-right symmetric models and the right-handed Kobayashi-Maskawa matrix

KL-KS mass difference is computed in a left-right symmetric model with three generations of quarks. Under the assumption of “manifest” left-right symmetry the mass of the right-handed charged gauge boson consistent withKL-KS constraint appears to be rather high. A low mass right-handed gauge boson can be accommodated in models with broken “manifest” left-right symmetry. The latter scenario has many non-trivial predictions for the decay of heavy (c, t, b) quarks.

Majorana Neutrinos and the Production of the Right-Handed Charged Gauge Boson

A possibility of a very clean signature for the production of ${{W}_{R}}^{\ifmmode\pm\else\textpm\fi{}}$ is pointed out. If the right-handed neutrino is lighter than ${{W}_{R}}^{\ifmmode\pm\else\textpm\fi{}}$, left-right symmetric gauge theory predicts the decay ${{W}_{R}}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{+}+2$ hadronic jets, with the branching ratio \ensuremath{\sim}3%. The lack of neutrinos in the final state and the absence of a sizable background make ${{W}_{R}}^{\ifmmode\pm\else\textpm\fi{}}$ rather easy to detect (if it exists). Detailed predictions regarding the production and decay rates of ${{W}_{R}}^{+}$ are presented.

Low-mass parity restoration, weak-interaction phenomenology, and grand unification

The question of low-energy restoration of parity is examined using a left-right-asymmetric model implied by the gauge group $\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(2)}_{R}\ifmmode\times\else\texttimes\fi{}\mathrm{U}{(1)}_{B\ensuremath{-}L}$ with ${g}_{L}g{g}_{R}$, both from a phenomenological point of view and also exploiting the possibility that such an asymmetry may be a consequence of two-stage symmetry breaking of $\mathrm{SU}{(2)}_{R}$ allowed in the SU(16) grand unification scheme. We carry out all the charged- and neutral-current tests with somewhat increased errors of the measured values of neutral-current parameters. The phenomenological asymmetric model passes all the tests permitting $1\ensuremath{\le}{(\frac{{g}_{L}}{{g}_{R}})}^{2}\ensuremath{\le}2$ and $0.23\ensuremath{\le}{{sin}^{2}\ensuremath{\theta}}_{W}\ensuremath{\le}0.29$, where the case $\frac{{g}_{L}}{{g}_{R}}=1$ corresponds to the symmetric model investigated by Rizzo and Senjanovic. Whereas low-energy parity restoration and low-mass gauge bosons may be possible in the symmetric model, the phenomenological asymmetric model allows a low-mass right-handed charged gauge boson (86-230 GeV) and a low-mass neutral boson (190-455 GeV), in addition to the two gauge bosons of first generation, but no parity restoration. It is shown that all the results of analysis of the phenomenological asymmetric model for the case of no mixing between the left- and right-handed charged gauge bosons still hold true in the case where the left-right asymmetry arises out of two-stage symmetry breaking of $\mathrm{SU}{(2)}_{R}$ allowed by SU(16) g\ifmmode \acute{r}\else \'{r}\fi{}and unification, but only with the replacement of the charged right-handed boson by a heavier one (g ${10}^{4}$ GeV). The SU(16) interpretation of left-right asymmetry and the available charged- and neutral-current data allows the observation of the second neutral boson together with the two gauge bosons of first generation, but no restoration of parity at ISABELLE energies. However, the parity restoration, if any, may be possible at energies \ensuremath{\gtrsim}${10}^{4}$ GeV. Several other observable distinctions of the asymmetric model from the standard one and the symmetric model with respect to the allowed regions and upper bounds on the allowed values of ${{sin}^{2}\ensuremath{\theta}}_{W}$ and the zeros of the neutral-current parameters and the variation of the second-neutral-$Z$-boson mass as functions of ${{sin}^{2}\ensuremath{\theta}}_{W}$ are pointed out. One of the particularly new features observed in this analysis is that for a large but fixed value of the coupling-constant ratio, the second-neutral-$Z$-boson mass increases with ${{sin}^{2}\ensuremath{\theta}}_{W}$.