Decay Of Right-handed Neutrinos Research Articles

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.

Right-handed sector leptogenesis

Instead of creating the observed baryon asymmetry of the universe by the decay ofright-handed (RH) neutrinos to left-handed leptons, we propose to generate it dominantlyby the decay of the RH neutrinos to RH leptons. This mechanism turns out to be successfulin large regions of parameter space. It may work, in particular, at a scale as lowas ∼TeV, with no need to invoke quasi-degenerate RH neutrino masses to resonantly enhance theasymmetry. Such a possibility can be probed experimentally by the observation at collidersof a singlet charged Higgs particle and of RH neutrinos. Other mechanisms which may leadto successful leptogenesis from the RH lepton sector interactions are also briefly presented.The incorporation of these scenarios in left–right symmetric and unified models isdiscussed.

NEUTRINO MASSES AND TeV SCALE RESONANT LEPTOGENESIS FROM SUPERSYMMETRY BREAKING

We review a class of supersymmetric models in which the light neutrino masses result from higher-dimensional supersymmetry-breaking terms in the MSSM super- and Kähler-potentials. The mechanism used in these models is closely related to the Giudice–Masiero mechanism for the MSSM μ parameter and leads to TeV-scale right-handed neutrino and sneutrino states. In these models, the dominant contribution to the light neutrino (Majorana) mass matrix is a one-loop term with a sub-dominant tree-level "seesaw" contribution. It is also shown that it is possible to construct a natural model of TeV-scale leptogenesis via the resonant behavior of the one-loop self-energy contribution to the right-handed neutrino (Ni) decay. This model addresses the primary problems of previous phenomenological studies of low-energy leptogenesis: a rational for TeV-scale right-handed neutrinos with small Yukawa couplings; the origin of the tiny, but non-zero mass splitting required between at least two Ni masses; and the necessary non-trivial breaking of flavor symmetries in the right-handed neutrino sector.

Right-handed neutrinos as the source of density perturbations

We study the possibility that cosmological density perturbations are generated by the inhomogeneous decay of right-handed neutrinos. This will occur if a scalar field whose fluctuations are created during inflation is coupled to the neutrino sector. Robust predictions of the model are a detectable level of non-Gaussianity and, if standard leptogenesis is the source of the baryon asymmetry, a baryon isocurvature perturbations at the level of the present experimental constraints.

Leptogenesis in minimal left–right symmetric models

We analyze lepton asymmetry induced in the decay of right-handed neutrinos in a class of minimal left–right symmetric models. In these models, which assume low energy supersymmetry, the Dirac neutrino mass matrix is proportional to the charged lepton mass matrix. As a result, lepton asymmetry is calculable in terms of 9 parameters, all measurable in low energy neutrino experiments. By solving the Boltzmann equations numerically we show that adequate baryon asymmetry is generated in these models. This however places significant constraints on the light neutrino parameters. We find tan 2 θ 12 ≃ m 1 / m 2 and θ 13 = ( 0.01 – 0.07 ) for the neutrino oscillation angles, and β ≃ α + π / 2 for the Majorana phases.

Neutrino texture saturating theCPasymmetry

We study a neutrino mass texture which can explain the neutrino oscillation data and also saturate the upper bound of the $CP$ asymmetry ${\ensuremath{\epsilon}}_{1}$ in the leptogenesis. We consider the thermal and nonthermal leptogenesis based on the right-handed neutrino decay in this model. A lower bound of the reheating temperature required for the explanation of the baryon number asymmetry is estimated as $O({10}^{8})\text{ }\mathrm{GeV}$ for the thermal leptogenesis and $O({10}^{6})\text{ }\mathrm{GeV}$ for the nonthermal one. It can be lower than the upper bound of the reheating temperature imposed by the cosmological gravitino problem. An example of the construction of the discussed texture is also presented.

Leptogenesis and rescattering in supersymmetric models

The observed baryon asymmetry of the Universe can be due to the $B-L$ violating decay of heavy right handed (s)neutrinos. The amount of the asymmetry depends crucially on their number density. If the (s)neutrinos are generated thermally, in supersymmetric models there is limited parameter space leading to enough baryons. For this reason, several alternative mechanisms have been proposed. We discuss the nonperturbative production of sneutrino quanta by a direct coupling to the inflaton. This production dominates over the corresponding creation of neutrinos, and it can easily (i.e. even for a rather small inflaton-sneutrino coupling) lead to a sufficient baryon asymmetry. We then study the amplification of MSSM degrees of freedom, via their coupling to the sneutrinos, during the rescattering phase which follows the nonperturbative production. This process, which mainly influences the (MSSM) $D-$flat directions, is very efficient as long as the sneutrinos quanta are in the relativistic regime. The rapid amplification of the light degrees of freedom may potentially lead to a gravitino problem. We estimate the gravitino production by means of a perturbative calculation, discussing the regime in which we expect it to be reliable.

Leptogenesis with almost degenerate Majorana neutrinos

We investigate leptogenesis with almost degenerate neutrinos in the framework of the democratic mass matrix, which naturally explains the large mixing angles for neutrino oscillations as well as quark masses and the mixing matrix. We find that the baryon asymmetry in the present universe is explained via the decays of right-handed neutrinos produced nonthermally by the inflaton decay. The model predicts neutrinoless double beta decays accessible in near future experiments.

Leptogenesis at the TeV scale

We present a general description of the problems encountered when attempting to build a simple model of leptogenesis and hence of baryogenesis at an energy scale as low as 1–10 TeV. We consider three possible lepton asymmetry enhancement mechanisms in the out-of-equilibrium decay scenario, emphasizing the three body decay mechanism as most natural. A new model based on the three body decays of right-handed neutrinos is proposed. It naturally allows both leptogenesis and neutrino mass generation at low scale. Also discussed is the possibility of inducing leptogenesis at low scale in existing neutrino mass models: Fukugita–Yanagida model, Higgs triplet model, Zee model and models with R-parity violation.

Decay and decoupling of heavy right-handed Majorana neutrinos in the L–R model

Heavy right-handed neutrinos are of current interest. The interactions and decay of such neutrinos determine their decoupling epoch during the evolution of the universe. This in turn affects various observable features like the energy density, nucleosynthesis, CMBR spectrum, galaxy formation, and baryogenesis. Here, we consider reduction of right-handed electron-type Majorana neutrinos, in the left-right symmetric model, by the WR+ - WR- channel and the channel originating from an anomaly, involving the SU(2)R gauge group, as well as decay of such neutrinos. We study the reduction of these neutrinos for different ranges of left-right model parameters, and find that, if the neutrino mass exceeds the right-handed gauge boson mass, then the neutrinos never decouple for realistic values of the parameters, but, rather, decay in equilibrium. Because there is no out-of-equilibrium decay, no mass bounds can be set for the neutrinos.

Leptogenesis and Yukawa textures

We study a set of textures giving rise to the correct masses and mixings of the charged fermions in the context of leptogenesis. The Dirac neutrino texture pattern is assumed to be identical with the up quark texture. The heavy Majorana neutrino mass matrix is obtained by inverting the type-I seesaw formula and using the neutrino masses and mixings required by the solar and atmospheric neutrino oscillation experiments as input. After making a feasibility study of the generated lepton asymmetry via the decay of the heavy right handed neutrino, we compute the generated baryon asymmetry by numerically solving the supersymmetric Boltzmann equations. We find for these models that both the hierarchy of the texture as well as the placement of the texture zeros are important to the viability of leptogenesis as the source of the observed baryon asymmetry of the universe.

Baryogenesis and lepton number violation

The cosmological baryon asymmetry can be explained by the nonperturbative electroweak reprocessing of a lepton asymmetry generated in the out-of-equilibrium decay of heavy right-handed Majorana neutrinos. We analyze this mechanism in detail in the framework of a SO(10)-subgroup. We take three right-handed neutrinos into account and discuss physical neutrino mass matrices.

MODEL FOR EFFICIENT MONOPOLE ANNIHILATION AND BARYOGENESIS

We present a model for efficient annihilation of magnetic monopoles which is accomplished by breaking the electromagnetic gauge invariance for an appropriate range of temperature during the radiation dominated epoch of the early universe. Except for the brief period when electromagnetism is broken, the gauge-group symmetry is SU (3)c × SU (2)L × U (1)Y between the grand unification and electroweak transition temperature scales. The model consists of a standard Higgs doublet, a charged singlet and an uncharged singlet, and it is shown to work for a very general set of parameters with none of the scalar coupling constants being, necessarily, either too large or too small. The uncharged singlet can easily give adequately large Majorana mass to the right-handed neutrinos making baryogenesis possible through the decay of heavy right-handed neutrinos and sphaleron interactions.

Baryogenesis via leptogenesis.

If right-handed Majorana neutrinos are added to the standard model, then lepton-number-violating out-of-equilibrium decays of right-handed neutrinos combined with anomalous electroweak processes can generate the baryon number of the Universe. We analyze this mechanism in detail, and determine the ranges of parameters for which the correct baryon number is generated. We find that the scenario works for a wide range of parameters in the neutrino sector, including right-handed neutrino masses ranging from \ensuremath{\sim}1 TeV to \ensuremath{\sim}${10}^{19}$ GeV, depending on the assumptions made about the structure of the neutrino mass matrices.

Distortion of the cosmic background radiation by radiative neutrino decay in a left-right symmetric model

We show that the recently observed distortion of the cosmic background radiation in the submillimeter region can be explained in terms of radiative decay of right-handed neutrinos in a left-right symmetric model.

Distortion of the cosmic background radiation by radiative neutrino decay in a left-right symmetric model

We show that the recently observed distortion of the cosmic background radiation in the submillimeter region can be explained in terms of radiative decay of right-handed neutrinos in a left-right symmetric model.