Left-right Symmetric Gauge Model Research Articles

Lepton mixing in gauge models

We reexamine lepton mixing in gauge models by considering two theories within the type I seesaw mechanism, the extended Standard Model, i.e. $SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{Y}$ with singlet right-handed heavy neutrinos, and the left-right model, $SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{R}\ifmmode\times\else\texttimes\fi{}U(1{)}_{B\ensuremath{-}L}$. The former is often used as a simple heuristic approach to masses and mixing of light neutrinos and to leptogenesis, while we consider the latter as an introduction to other left-right symmetric gauge theories like $SO(10)$. We compare lepton mixing in both theories for general parameter space and discuss also some particular cases. In the electroweak broken phase, we study in parallel both models in the current basis (diagonal gauge interactions) and in the mass basis (diagonal mass matrices and mixing in the interaction), and perform the counting of $CP$-conserving and $CP$-violating parameters in both bases. We extend the analysis to the Pati-Salam model $SU(4{)}_{C}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{R}$ and to $SO(10)$. Although specifying the Higgs sector increases the predictive power, in the most general case one has the same parameter structure in the lepton sector for all the left-right symmetric gauge models. We make explicit the differences between the extended Standard Model and the left-right models, in particular $CP$-violating and lepton-number-violating new terms involving the ${W}_{R}$ gauge bosons. As expected, at low energy, the differences in the light neutrino spectrum and mixing appear only beyond leading order in the ratio of the Dirac mass to the right-handed Majorana mass.

Search for the right-handed W R boson and a heavy neutrino at the Large Hadron Collider

We present a brief review of the SU c (3)⊗SU L (2)⊗SU R (2)⊗U(1) left-right symmetric gauge model. We discuss a possibility of detecting the right-handed W R boson and a heavy neutrino in pp collisions at the Large Hadron Collider. We present restrictions on the masses of the W R boson and the heavy neutrino obtained using the analysis of experimental data from the CMS and ATLAS detectors with a total energy of colliding protons of 7–8 TeV.

Search for the right-handed boson W R and heavy neutrino

The SUc(3) ⊗ SUL(2) ⊗ SUR(2) ⊗ U(1) left-right symmetric gauge model has been briefly reviewed. The possibility of the detection of signals from the production of the WR boson in pp-collisions at the Large Hadron Collider has been discussed. Constraints on the masses of the WR-boson and heavy neutrino obtained by analyzing the recent experimental data from the Compact Muon Solenoid detector with the total energy of collisions Etot = 8 TeV have been reviewed.

Searching for dark matter signals in the left-right symmetric gauge model withCPsymmetry

We investigate singlet scalar dark matter (DM) candidate in a left-right symmetric gauge model with two Higgs bidoublets (2HBDM) in which the stabilization of the DM particle is induced by the discrete symmetries P and CP. According to the observed DM abundance, we predict the DM direct and indirect detection cross sections for the DM mass range from 10 GeV to 500 GeV. We show that the DM indirect detection cross section is not sensitive to the light Higgs mixing and Yukawa couplings except the resonance regions. The predicted spin-independent DM-nucleon elastic scattering cross section is found to be significantly dependent on the above two factors. Our results show that the future DM direct search experiments can cover the most parts of the allowed parameter space. The PAMELA antiproton data can only exclude two very narrow regions in the 2HBDM. It is very difficult to detect the DM direct or indirect signals in the resonance regions due to the Breit-Wigner resonance effect.

Lepton flavour violation in a left-right symmetric model

We consider in this paper a Left-Right symmetric gauge model in which a global lepton-number-like symmetry is introduced and broken spontaneously at a scale that could be as low as 10^4 GeV or so. The corresponding physical Nambu-Goldstone boson, which we call majoron and denote J, can have tree-level flavour-violating couplings to the charged fermions, leading to sizeable majoron-emitting lepton-flavour-violating weak decays. We consider explicitly a leptonic variant of the model and show that the branching ratios for \mu -> e+J, \tau -> e + J and \tau -> \mu + J decays can be large enough to fall within the sensitivities of future \mu and \tau factories. On the other hand the left-right gauge symmetry breaking scale may be as low as few TeV.

Left-right symmetric gauge model with new h− ξR interactions

The Yang-Mills-Higgs Lagrangian of the left-right symmetric gauge model with the symmetry of SU(3) c × SU(2) L× SU(2) R× U(1) is presented by considering the new interaction terms between SU(2) L bidoublet Higgs boson h and SU(2) R adjoint Higgs boson ξ R. We also present a parametrization of the Higgs potential and interacting terms in such a way that not only does the cosmological constant vanishes at the tree level but also the light Higgs field emerges without fine tuning of parameters. ξ R is responsible for the spontaneous breakdown of SU(2) R× U(1) down to U(1) Y and the seesaw mechanism of neutrino mass is well explained owing to this symmetry breakdown. The Higgs boson h yields the spontaneous breakdown of SU(2) L× U(1) Y down to U(1) em. Due to this new interaction term together with other interaction and potential terms of the Higgs bosons, only one CP-even scalar boson among the bidoublet boson h survives in the weak energy scale and other four scalar bosons acquire the mass of the SU(2) R× U(1) breaking scale, which leads to the same situation as in the standard model.

Composite Weak Vector Bosons in a Left-Right Symmetric Preon Model

We take the viewpoint that the standard model is a low energy effective theory among composite quarks, leptons and weak bosons in a left-right (LR) symmetric preon model with a hypercolor SU(N)HC gauge interaction. Starting from NJL-type interactions with global SU(2h x SU(2h symmetry, we construct the composite weak vector bosons from a pair of spinor preons and derive their effective interactions with quarks and leptons, which are essentially identical, at the tree­ diagram level, to those in the LR symmetric gauge model. Through the process of this approach, some physical aspects of the LR gauge model are clarified.

Reconstruction of the spontaneously broken gauge theory in non-commutative geometry

The scheme previously proposed by the present authors is modified to incorporate the strong interaction by affording the direct product internal symmetry. We do not need to prepare the extra discrete space for the colour gauge group responsible for the strong interaction to reconstruct the standard model and the left-right symmetric gauge model (LRSM). The approach based on non-commutative geometry leads us to present many attractive points such as the unified picture of the gauge and Higgs field as the generalized connection on the discrete spaceM4×ZN. This approach leads us to unified picture of gauge and Higgs fields as the generalized connection. The standard model needsN=2 discrete space for reconstruction in this formalism. LRSM is still alive as a model with the intermediate symmetry of the spontaneously brokenSO(10) grand unified theory (GUT).N=3 discrete space is needed for the reconstruction of LRSM to include two Higgs bosonsφ andξ which are as usual transformed as (2, 2*, 0) and (1, 3, −2) underSU(2)L×SU(2)R×U(1)Y, respectively.ξ is responsible to makeνR Majorana fermion and so well explains the seesaw mechanism. Up and down quarks have different masses through the vacuum expectation value ofφ.

Mass mixing, CP violation and left-right symmetry for heavy neutral mesons

We investigate\(M^0 - \bar M^0 \) mixing and CP violation in the minimal left-right symmetric gauge model with spontaneous P and CP violation. The dominant contributions to the mixing amplitude including QCD corrections are calculated explicitly for\(B^0 - \bar B^0 \). While the amount of mixing is not much changed with respect to the standard model leftright symmetry can give rise to significantly larger CP violation in the\(B_s^0 - \bar B_s^0 \) system (up to two orders of magnitude for the dilepton charge asymmetry). Sizable CP violating effects require that the left-right contribution to theK L K S mass difference has the same sign as the standard model contribution. We also comment on\(D^0 - \bar D^0 \) mixing including a careful discussion of the standard model prediction for the short distance part.

Derivation of very tiny masses of neutrinos in the left-right symmetric gauge model

Very tiny mass values of neutrinos are derived in the left-right symmetric gauge model with spontaneous parity violation. In our scheme the Dirac mass terms of neutrinos vanish in the tree level, but they are induced in higher order and proportional to the charged-lepton mass terms. The relation, m ν l ⋍ G 0m l 2 m WR , with G 0⪅10 −13 for the three generations, is derived. We also discuss the model where the mixings among the lepton generations vanish.

Ultralight Dirac neutrinos in a left-right symmetric model containing mirror fermions

We propose a low energy, left-right symmetric gauge model incorporating mirror fermions that naturally produces ultralight Dirac neutrinos (<100 eV). The numbers of standard and mirror generations must be equal to prevent neutrino masses in the cosmologically-disfavored range 100 eV ⩽ M v ⩽ 2 GeV. Our model is consistent with the experimental limits on rare processes.

ε, ε′ in a model with spontaneous P and CP violation

ε, ε′, the K LK S mass difference and the neutron electric dipole moment are calculated in a minimal left-right symmetric gauge model with spontaneous P and CP violation. For M W 2 in the several TeV range the model satisfies all experimental constraints. ε′/ ε may be negative and is found to be less than 10 −2 in absolute magnitude.

Dirac neutrino mass in a left-right symmetric gauge model

It is shown that it is possible to get a small mass for Dirac neutrino in a left-right symmetric gauge model in a natural manner. The smallness of the neutrino mass is related to the smallness of the right-handed weak interactions.

A Left-Right Symmetric Gauge Model as an Extended Weinberg-Salam Theory

The minimal extension of the Weinberg-Salam theory satisfying left-right symmetry and quark-lepton unification is given by SU, (4) Q9 {SU L (2)Q9SU R (2)}. Its spontaneous breakdowns to SU, (3) Q9 {SU L(2)Q9U(1)} and then to SU,(3)Q9U,m (1) are ascribed to two Higgs multiplets. A relation between two mixing angles associated with these breakdowns is obtained. The mass scale of the first breakdown is estimated by the renormalization group method to be 10- GeV.

Neutral currents in left-right symmetric gauge models

We analyse all the neutral-current phenomena following from the general class of gauge models based on the group SU(2) L ⊗ SU(2) R ⊗ U(1). It is found that the neutral-current couplings in these models bear a remarkable similarity to those in the standard Weinberg-Salam gauge model. The parameter which plays the role of sin2ϑw is found to lie between 0 and 1/2. Comparison with experimental data shows that even a model with the ratio of the masses of the twoZ bosons as small as 1.9 is not ruled out.

Parity violation in atoms within left-right symmetric gauge models

Predictions for parity violation in atoms within left-right symmetric theories based on the gauge groups SU(2) L × SU(2) R × U(1) and SU(2) L × SU(2) L × SU(2) R × U(1) L × U(1) R are presented.

Parity violation in left-right symmetric gauge models

The parity violating effective interaction in models based on the SU(2) L × SU(2) R × U(1) gauge group is shown to have the same structure, at zero momentum transfer, as in the Weinberg-Salam model, apart from a constant scale factor.

Parity violation in SLAC experiment and left-right symmetric gauge models

It is shown that the left-right symmetric gauge models based on the group G = SU(2) L × SU(2) R × U(1) L × U(1) R can accommodate quite naturally the results of the recent SLAC experiment concerning parity violation in neutral currents. The possibility of finding a light neutral gauge boson in the PETRA-PEP energy range remains particularly interesting.

Cabibbo angle, CP violation and quark masses

By adding suitable discrete flavor symmetries to SU(2) L ⊗ SU(2) R ⊗ U(1) left-right symmetric gauge models of weak and electromagnetic interactions, we are able to express all the mixing angles between the quark flavors (u, d, s,c) in terms of the quark masses. This enables us to compute the Cabibbo angle and the CP violating phases using plausible values for the quark masses. The CP violating K ar 2 π decay amplitude η +− (and η 00 in the model is then given purely in terms of the parity violating parameter of the model ( m W L +/ m W R +) 2 .

Left-right symmetric gauge models and possible existence of a neutral gauge boson with mass in the PETRA-PEP energy range

We study the neutral-current weak interaction sector of a class of gauge models of weak and electromagnetic interactions based on the left-right symmetric gauge group SU (2) L × SU (2) R × U (1) L × U (1) R. The most interesting conclusions are: (i) to order G F, the predictions for neutrino-induced interactions are equivalent to those of the Salam-Weinberg model; (ii) parity violation in atoms can be arranged to be zero to order G F; (iii) weak-electromagnetic interference effects distinguish between the various models in the class, which includes the Salam-Weinberg model and other left-right symmetric gauge models as special cases; (iv) one of the neutral gauge bosons is permitted to have a mass in the PETRA-PEP energy range.