Class Of Left-right Symmetric Models Research Articles

Flavor physics constraints on left-right symmetric models with universal seesaw

We study the phenomenological constraints on the parameter space of a class of left-right symmetric models in which the fermion masses are generated through a universal seesaw mechanism. Motivated by the axionless solution to the strong CP problem, the model features a simple Higgs sector consisting of left- and right-handed doublets. The fermion masses are then generated through their mixing with heavy vector-like fermions, which leads to flavor changing neutral currents arising at tree-level and also introduces non-unitarity in the charged current interactions. These new contributions induce flavor and flavor-universality violating processes which are used to derive constraints on the parameter space of the model. We also argue that although the model has the potential to resolve flavor anomalies, it falls short in the case of B-anomalies RK(⁎) and anomalous magnetic moment of muon aμ.

A theory of R(D*, D) anomaly with right-handed currents

We present an ultraviolet complete theory for the R(D*) and R(D) anomaly in terms of a low mass WR± gauge boson of a class of left-right symmetric models. These models, which are based on the gauge symmetry SU(3)c × SU(2)L × SU(2)R × U(1)B − L, utilize vector-like fermions to generate quark and lepton masses via a universal seesaw mechanism. A parity symmetric version as well as an asymmetric version are studied. A light sterile neutrino emerges naturally in this setup, which allows for new decay modes of B-meson via right-handed currents. We show that these models can explain R(D*) and R(D) anomaly while being consistent with LHC and LEP data as well as low energy flavor constraints arising from {K}_L-{K}_S,kern0.5em {B}_{d,s}-{overline{B}}_{d,s},kern0.5em D-overline{D} mixing, etc., but only for a limited range of the WR mass: 1.2 (1.8) TeV ≤ {M}_{W_R} ≤ 3 TeV for parity asymmetric (symmetric) Yukawa sectors. The ratio R(D)/R(D*) is predicted to be ≃ 1.16, which is the same as in the Standard Model. The light sterile neutrinos predicted by the model may be relevant for explaining the MiniBoone and LSND neutrino oscillation results. The parity symmetric version of the model provides a simple solution to the strong CP problem without relying on the axion. It also predicts an isospin singlet top partner with a mass MT = (1.5 − 2.5) TeV.

Light sterile neutrino and dark matter in left-right symmetric models without a Higgs bidoublet

We present a class of left-right symmetric models where Dirac as well as Majorana mass terms of neutrinos can arise at one-loop level in a scotogenic fashion: with dark matter particles going inside the loop. We show the possibility of naturally light right handed neutrinos that can have interesting implications at neutrinoless double beta decay experiments as well as cosmology. Apart from a stable dark matter candidate stabilised by a remnant $Z_2$ symmetry, one can also have a long lived keV sterile neutrino dark matter in these models. This class of models can have very different collider signatures compared to the conventional left-right models.

Neutrinoless double beta decay in LRSM with natural type-II seesaw dominance

We present a detailed discussion on neutrinoless double beta decay within a class of left-right symmetric models where neutrino mass originates by natural type-II seesaw dominance. The spontaneous symmetry breaking is implemented with doublets, triplets and bidoublet scalars. The fermion sector is extended with an extra sterile neutrino per generation that helps in implementing the seesaw mechanism. The presence of extra particles in the model exactly cancels type-I seesaw and allows large value for Dirac neutrino mass matrix $M_D$. The key feature of this work is that all the physical masses and mixing are expressed in terms of neutrino oscillation parameters and lightest neutrino mass thereby facilitating to constrain light neutrino masses from $0\nu\beta\beta$ decay. With this large value of $M_D$ new contributions arise due to; i) purely left-handed current via exchange of heavy right-handed neutrinos as well as sterile neutrinos, ii) the so called $\lambda$ and $\eta$ diagrams. New physics contributions also arise from right-handed currents with right-handed gauge boson $W_R$ mass around $3$~TeV. From the numerical study, we find that the new contributions to $0\nu\beta\beta$ decay not only saturate the current experimental bound but also give lower limit on absolute scale of lightest neutrino mass and favor NH pattern of light neutrino mass hierarchy.

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.

Double beta decay, lepton flavor violation, and collider signatures of left-right symmetric models with spontaneousD-parity breaking

We propose a class of left-right symmetric models (LRSMs) with spontaneous D parity breaking, where SU(2)_R breaks at the TeV scale while discrete left-right symmetry breaks around 10^9 GeV. By embedding this framework in a non-supersymmetric SO(10) Grand Unified Theory (GUT) with Pati-Salam symmetry as the highest intermediate breaking step, we obtain g_R / g_L ~ 0.6 between the right- and left-handed gauge couplings at the TeV scale. This leads to a suppression of beyond the Standard Model phenomena induced by the right-handed gauge coupling. Here we focus specifically on the consequences for neutrinoless double beta decay, low energy lepton flavour violation and LHC signatures due to the suppressed right handed currents. Interestingly, the reduced g_R allows us to interpret an excess of events observed recently in the range of 1.9 TeV to 2.4 TeV by the CMS group at the LHC as the signature of a right handed gauge boson in LRSMs with spontaneous D parity breaking. Moreover, the reduced right-handed gauge coupling also strongly suppresses the non-standard contribution of heavy states to the neutrinoless double beta decay rate as well as the amplitude of low energy lepton flavour violating processes. In a dominant type-II Seesaw mechanism of neutrino mass generation, we find that both sets of observables provide stringent and complimentary bounds which make it challenging to observe the scenario at the LHC.

Leptogenesis bound on neutrino masses in left-right symmetric models with spontaneousD-parity violation

We study the baryogenesis via leptogenesis in a class of left-right symmetric models, in which $D$-parity is broken spontaneously. We first discuss the consequence of the spontaneous $D$-parity breaking on the neutrino masses. Than we study the lepton asymmetry in various cases, from the decay of right handed neutrino as well as the triplet Higgs, depending on their relative masses they acquire from the symmetry breaking pattern. The leptogenesis bound on their masses are discussed by taking into account the low energy neutrino oscillation data. It is shown that a TeV scale leptogenesis is viable if there are additional sources of CP violation like domain wall originating from the spontaneous $D$-parity violation.

Bounds on neutrino masses from leptogenesis in type-II seesaw models

The presence of the triplet ${\ensuremath{\Delta}}_{L}$ in left-right symmetric theories leads to type-II seesaw mechanism for the neutrino masses. In these models, assuming a normal mass hierarchy for the heavy Majorana neutrinos, we derive a lower bound on the mass of the lightest of heavy Majorana neutrinos from the leptogenesis constraint. From this bound we establish a consistent picture for the hierarchy of heavy Majorana neutrinos in a class of left-right symmetric models in which we identify the neutrino Dirac mass matrix with that of Fritzsch type charged lepton mass matrix. It is shown that these values are compatible with the current neutrino oscillation data.

CP Violation in Hyperon Decays due to Left-Right Mixing.

We consider the CP violating asymmetry A in polarization in hyperon and antihyperon decays due to left-right mixing in a class of left-right symmetric models. We find that the gluon dipole penguin operator dominates the contributions to the CP violating asymmetry. For $\ensuremath{\Lambda}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{\ensuremath{-}}$, even though the S-wave contribution to A is constrained from experimental data on ${\ensuremath{\epsilon}}^{\ensuremath{'}}/\ensuremath{\epsilon}$, A can be as large as ${10}^{\ensuremath{-}4}$. For P wave, the contribution is not directly related to ${\ensuremath{\epsilon}}^{\ensuremath{'}}/\ensuremath{\epsilon}$. A can be even larger, and may reach $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. This is much larger than the value expected for A in the standard model.