Minimal Left-right Symmetric Model Research Articles

Relating leptogenesis to low energy flavor violating observables in models with spontaneousCPviolation

In the minimal left-right symmetric model, there are only two intrinsic $CP$ violating phases to account for all $CP$ violation in both the quark and lepton sectors, if $CP$ is broken spontaneously by the complex phases in the VEV's of the scalar fields. In addition, the left- and right-handed Majorana mass terms for the neutrinos are proportional to each other due to the parity in the model. This is thus a very constrained framework, making the existence of correlations among the $CP$ violation in leptogenesis, neutrino oscillation and neutrinoless double beta decay possible. In these models, $CP$ violation in the leptonic sector and $CP$ violation in the quark sector are also related. We find, however, that such connection is rather weak due to the large hierarchy in the bi-doublet VEV required by a realistic quark sector.

Symmetry breaking of the symmetric left-right model without a scalar bidoublet

By invoking the existence of a general custodial O(2) symmetry, a minimal Left-Right symmetric model based on the gauge group G=SU(2)L SU(2)R U(1)BL is shown to require the existence of only two physical Higgs bosons. The lighter Higgs is predicted to have a small mass which could be evaluated by standard perturbation theory. The fermionic mass matrices are recovered by insertion of ad hoc fermion-Higgs interactions. The model is shown to be undistinguishable from the standard model at the currently reachable energies.

The minimal left-right symmetric model and radiative corrections to the muon decay

A self-consistent version of the left-right (LR) symmetric model is used to examine tree- as well as one-loop level radiative corrections to the muon decay. It is shown that constraints on the heavy sector of the model parameters are different when going beyond tree-level physics. In fact, in our case, the only useful constraints on the model can be obtained from the one-loop level calculation. Furthermore, corrections coming from the subset of SM particles within the LR model have a different structure from their SM equivalent, e.g. the top quark leading term contribution to Δϱ within the LR model is different from its SM counterpart. As a consequence, care must be taken in fitting procedures of models beyond the SM, where usually, only tree-level couplings modified by the SM radiative corrections are considered. This procedure is not always correct.

Higgs sector of the minimal left-right symmetric model

We perform an exhaustive analysis of the most general Higgs sector of the minimal left-right symmetric model (MLRM). We find that the $\mathit{CP}$ properties of the vacuum state are connected to the Higgs spectrum: if $\mathit{CP}$ is broken spontaneously, the MLRM does not approach the standard model in the limit of a decoupling left-right symmetry breaking scale. Depending on the size of the $\mathit{CP}$ phases, scenarios with extra nondecoupling flavor-violating doublet Higgs bosons or very light SU(2) triplet Higgs bosons emerge, both of which are ruled out by phenomenology. For zero $\mathit{CP}$ phases the nonstandard Higgs bosons decouple only if a very unnatural fine-tuning condition is satisfied. We also discuss generalizations to the nonminimal Higgs sector.

Neutrino masses and a low breaking scale of left-right symmetry

In left-right symmetric models (LRSMs) the light neutrino masses arise from two sources: the seesaw mechanism and a vacuum expectation value of an $\mathrm{SU}{(2)}_{L}$ triplet. If the left-right symmetry breaking ${v}_{R}$ is low, ${v}_{R}\ensuremath{\lesssim}15 \mathrm{TeV},$ the contributions to the light neutrino masses from both the seesaw mechanism and the triplet Yukawa couplings are expected to be well above the experimental bounds. We present a minimal LRSM with an additional U(1) symmetry in which the masses induced by the two sources are below the eV scale and the twofold problem is solved. We further show that, if the U(1) symmetry is also responsible for the lepton flavor structure, the model yields a small mixing angle within the first two lepton generations.

Topological defects in the left-right symmetric model and their relevance to cosmology

It is shown that the minimal left-right symmetric model admits cosmic string and domain wall solutions.

Topological defects in the left-right symmetric model and their relevance to cosmology

It is shown that the minimal left-right symmetric model admits cosmic string and domain wall solutions. The cosmic strings arise when the SU(2)_R is broken and can either be destabilized at the electroweak scale or remain stable through the subsequent breakdown to U(1)_{EM}. The strings carry zero modes of the neutrino fields. Two distinct domain wall configurations exist above the electroweak phase transition and disappear after that. Thier destablization provides new sources of non-equilibrium effects below the electroweak scale which is relevant to baryogenesis.

Electroweak phase transition in left-right symmetric models

We study the finite-temperature effective potential of minimal left-right symmetric models containing a bidoublet and two triplets in the scalar sector. We perform a numerical analysis of the parameter space compatible with the requirement that baryon asymmetry is not washed out by sphaleron processes after the electroweak phase transition. We find that the spectrum of scalar particles for these acceptable cases is consistent with present experimental bounds.

Minimal supersymmetric left-right model

We construct the truly minimal left-right symmetric model by utilizing only the fields dictated by supersymmetry and automatic R-parity conservation. Allowing for non-renormalizable operators in the superpotential, we show that parity can be spontaneously broken while preserving electromagnetic gauge invariance. The scale of parity breakdown is predicted in the intermediate region: $M_R > 10^{10}- 10^{11} GeV$, and R-parity remains exact. The theory contains a number of charged and doubly charged Higgs scalars with a low mass of order $M_R^2/M_{Planck}$, accessible to experiment.

Effects of e+e- nu e decays of tau neutrinos near a supernova.

We revisit the constraints implied by SN 1987 A observations on the decay rate of a multi-MeV $\nu_\tau$ decaying into the visible channel $\nu_\tau \rightarrow e^+ e^- \nu_e$, if its lifetime is more than 10 {\it sec.}. We discuss its implication for the minimal left-right symmetric model with see-saw mechanism for neutrino masses. We also speculate on the possible formation of a ``giant Capacitor" in intergalactic space due to the decay of "neutronization" $\nu_\tau$'s and spin allignment possibility in the supernova.

Muonium to antimuonium conversion and the decay micro+-->e+ nu -bare nu micro in left-right symmetric models.

We show that in the minimal left-right symmetric model with triplet Higgs bosons the range of the muon neutrino mass for which {nu}{sub {mu}} is required by cosmological considerations to be unstable can be probed by muonium to antimuonium conversion ({ital M}{r arrow}{ital {bar M}}) and/or by the exotic muon decay {mu}{sup +}{r arrow}{ital e}{sup +} {bar {nu}}{sub {ital e}}{nu}{sub {mu}}. We point out that if all the leptonic mixing matrices are hierarchical and the Dirac masses of the neutrinos are equal to the masses of the corresponding charged leptons, there is a lower bound in this range for the rates of both of these processes. We find {vert bar}{ital G}{sub {ital M}{ital {bar M}}}{vert bar}{approx gt}7{times}10{sup {minus}5}{ital G}{sub {ital F}} and {vert bar}{ital G}{sub {mu}}{sup ({ital e})}{vert bar}{approx gt}2{times}10{sup {minus}4}{ital G}{sub {ital F}} for the strength of the {ital M}{r arrow}{ital {bar M}} and {mu}{sup +}{r arrow}{ital e}{sup +} {bar {nu}}{sub {ital e}}{nu}{sub {mu}} interactions.

Minimal left-right symmetry and SO(10) grand unification using LEP coupling constant measurements

We consider embedding the standard model in a minimal left-right symmetric model. The left-right symmetry breaking is characterised by a scale M R, and accordingly the running of the couplings is modified above M R. This model can in turn be embedded in SO(10) grand unification, if the couplings evolve to a single unification point. Neglecting threshold effects, we find that this will occur for M R=10 10.44±0.33 GeV. The corresponding scale of unification is found to be M X=10 15.20 ±0.25GeV, which is not in conflict with the proton lifetime bound.

Renormalisation group analysis of the minimal left-right symmetric model

We give the one-loop renormalisation group equations for the minimal left-right symmetric model containing two triplets and one bi-doublet Higgs. Assuming this model to be only an effective low-energy theory, we give upper bounds on the top quark mass and the Majorana mass of the right-handed neutrino as a function of the cutoff scale. We also give a qualitative discussion of the behaviour of the couplings in the Higgs sector.

$$B^0 - \bar B^0 $$ mixing within and beyond the standard model

The standard model with three fermion families is found to be compatible with the Argus observation of a relatively large amount of\(B_{^d }^0 - \bar B_d^0 \) mixing provided that the top quark is rather heavy. From an analysis of the existing information on mixing angles, and of the constraints imposed by the kaon system, in particular by the e parameter, we conclude that almost certainlym t 90 GeV. In view of the Argus result the standard model unambiguously leads to the prediction of a nearly maximal amount of\(B_{^s }^0 - \bar B_s^0 \) mixing. Apart from the rather obvious case of a fourth family of quarks, most “minimal” extensions of the standard model preserve the prediction of a large\(B_{^s }^0 - \bar B_s^0 \) mixing. We discuss\(B^0 - \bar B^0 \) mixing in minimal supersymmetric models compatible with the UA1 lower bounds on gluino and squark masses. Contributions from charged Higgs exchange in the box diagrams are also discussed. While supersymmetry (although marginally) and charged Higgses can lead to an appreciable enhancement of\(B^0 - \bar B^0 \) mixing, minimal left-right symmetric models actually predict a modest suppression of the effect with respect to the standard model.

Is The Left-Right Higgs Sector Observable?

We examine the allowed mass range of the charged Higgs field H+ in a minimal left-right symmetric model. We find that the mass of this Higgs is nearly degenerate with the mass of the flavor-changing neutral Higgs, and this implies MH+≳5~10 TeV. We examine a number of solutions, but fail to evade this restriction. If this constraint can not be avoided, the H+ (and very likely all other left-right extended Higgs particles) would be virtually undetectable at all experimental facilities, including the SSC.

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.

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.

N = 1 supergravity within the minimal left-right symmetric model

We present a model which links N = 1 supergravity with the minimal left-right symmetric model, based on the gauge symmetry SU(2) L × SU(2) R × U(1) B− L and a minimal set of Higgs fields. The gravitino mass, which is the only relevant low energy scale for the model, sets the scale for the mass of W R, while the mass of W L arises radiatively. It is observed that barring unnatural fine tuninng of parameters, the hierarchy ratio ν = ( m W R / m W L is bounded above by a number of order ten. The mass spectrum of the model bearing the richness expected of left-right as well as supersymmetry is presented.