Discrete Left-right Symmetry Research Articles

Leptogenesis from low-energy CP violation in minimal left-right symmetric model

We perform a thermal unflavored leptogenesis analysis on minimal left-right symmetric models with discrete left-right symmetry identified as generalized parity or charge conjugation. When left-right symmetry is unbroken in the lepton Yukawa sector, the neutrino Dirac coupling matrix is completely determined by neutrino masses and mixing angles, allowing CP violation needed to generate leptogenesis totally resides in the low-energy sector. With two lepton asymmetry generation ways, both type I and mixed type I+II neutrino mass generation mechanisms are considered. After solving the Boltzmann equations numerically, we find that the low-energy CP phases in the lepton mixing matrix can successfully produce the observed baryon asymmetry, and in some cases, the Dirac CP phase can be the only source of CP violation. Finally, we discuss the interplay among low-energy CP phase measurements, leptogenesis, and neutrinoless double beta decay. We show that the viable models for successful leptogenesis can be probed in next-generation neutrinoless double-beta decay experiments.

Threshold effects on prediction for proton decay in non-supersymmetric E6 GUT with intermediate trinification symmetry

We consider a non-supersymmetric E6 Grand Unified Theory (GUT) with intermediate trinification symmetry SU(3)C×SU(3)L×SU(3)R×D (D denoted as D-parity for discrete left-right symmetry) and study the effect of one-loop threshold corrections arising due to every class of superheavy particles (scalars, fermions and vectors). It is observed that, the intermediate mass scale MI and sin2⁡θW remain unaffected by GUT threshold contributions. The threshold modified unification mass scale MU is in excellent agreement with the present experimental proton decay constraint. The novel feature of the model is that GUT threshold uncertainty of MU is found to be controlled by superheavy scalars only, leading to a very predictive scenario for proton decay, which can be verifiable within the foreseeable experiments.

Time-reversal symmetry violation in several Lepton-Flavor-Violating processes

We compute a T-odd triple vector correlation for the $\mu\rightarrow e\gamma $ decay and the $\mu\rightarrow e$ conversion process. We find simple results in terms of the CP violating phases of the effective Hamiltonians. Then we focus on the minimal Left-Right symmetric extension of the Standard Model, which can lead to an appreciable correlation. We show that under rather general assumptions, this correlation can be used to discriminate between Parity or Charge-conjugation as the discrete Left-Right symmetry.

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.

Coannihilation scenarios and particle spectroscopy inSU(4)c×SU(2)L×SU(2)R

We identify a variety of coannihilation scenarios in a supersymmetric $SU(4{)}_{c}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{L}\ifmmode\times\else\texttimes\fi{}SU(2{)}_{R}$ model with discrete left-right symmetry. Nonuniversal gaugino masses, compatible with the gauge symmetry, play an essential role in realizing gluino and bino-wino coannihilation regions that are consistent with the WMAP dark matter constraints. We also explore regions of the parameter space in which the little hierarchy problem is partially resolved. We present several phenomenologically interesting benchmark points and the associated sparticle and Higgs mass spectra.

Fermion masses and coupling unification inE6:Life in the desert

We present an ${E}_{6}$ grand unified model with a realistic pattern of fermion masses. All standard model fermions are unified in three fundamental 27-plets (i.e., supersymmetry is not invoked), which involve in addition right-handed neutrinos and three families of vectorlike heavy quarks and leptons. The lightest of those can lie in the low-TeV range, being accessible to future collider experiments. As a result of the high symmetry, the masses and mixings of all fermions are closely related. The new heavy fermions play a crucial role for the quark and lepton mass matrices and the bilarge neutrino oscillations. In all channels generation mixing and $\mathcal{C}P$ violation arise from a single antisymmetric matrix. The ${E}_{6}$ breaking proceeds via an intermediate-energy region with ${\mathrm{SU}(3)}_{L}\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}(3)}_{R}\ifmmode\times\else\texttimes\fi{}{\mathrm{SU}(3)}_{C}$ gauge symmetry and a discrete left-right symmetry. This breaking pattern leads in a straightforward way to the unification of the three gauge coupling constants at high scales, providing for a long proton lifetime. The model also provides for the unification of the top, bottom, and tau Yukawa couplings and for new interesting relations in flavor and generation space.

How natural is a smallθ¯in left-right supersymmetry models?

In the world without an axion the smallness of $\bar\theta$ may be achieved due to a spontaneously broken discrete left-right symmetry. We analyze the radiatively induced \bar\theta in the context of generic left-right symmetric SUSY models without assuming flavor degeneracy in the squark sector. Left-right symmetry allows to keep \bar\theta within its present bound only if the inter-generational mass splitting in the squark sector at the scale of the left-right symmetry breaking is smaller than 0.5%. We also consider the naturalness of m_u=0 solution to the strong CP problem in the context of horizontal flavor symmetries. A strong bound on the combination of the horizontal charges in the Up quark sector is found in this case.

Symmetry-breaking density profiles in confined liquids.

Density profiles of a liquid confined between two parallel plates are studied near a liquid-gas transition. The system is additionally exposed to an external field depending on the coordinate perpendicular to the plates that possesses a discrete left-right symmetry with respect to the midplane between the plates. It is found that the equilibrium density profiles can be symmetry breaking, i.e., they do not possess the discrete left-right symmetry of the external field. Explicit results are obtained within a simple double-slit model consisting of two layers of two-dimensional Lennard-Jones systems using both computer simulation and density-functional theory. Such symmetry-breaking profiles should be observable in confined colloidal suspensions.

The Voloshin-Vysotski-Okun solution to the solar-neutrino problem in a left-right model

The apparent anticorrelation between the solarneutrino flux and the sun-spot number can be explained if electron neutrino has a large magnetic moment. A model with SU(2) L ×SU(2) R ×U(1) B−l gauge interaction is presented in which the electron neutrino has a large magnetic moment. The ingredients of the model are (i) the absence of the usual discrete left-right symmetry, (ii) new fermions that are singlets under SU(2) L and SU(2) R and (iii) two doublets and a charged singlet of higgs. The model utilises the see-saw mechanism of Gell-Mann, Ramond and Slansky give masses to all quarks and leptons. The large magnetic moment of the electron neutrino is achieved through charged singlet higgs fields.

Left-right symmetric theories and vacuum domain walls and strings

Theories in which a discrete left-right symmetry is spontaneously broken are expected to lead to the formation of vacuum domain walls. Although the existence of such walls at the present epoch is observationally excluded, we show that such theories are allowed if the discrete symmetry is embedded in a larger continuous symmetry, e.g., SO(10), spontaneously broken at higher temperatures. In this case vacuum strings are formed when the larger symmetry is broken, and these become connected by domain walls when the discrete symmetry is broken. The bounded domain walls tend to shrink, and the system of strings and domain walls decays before its energy density becomes comparable to that of matter. In particular, our arguments allow the symmetry breaking pattern SO(10) → … S[O(6)×O(4)] → SU(3)×SU(2)×U(1) which has been proposed by others.