Heavy Right-handed Majorana Neutrinos Research Articles

Majorana Neutrino Oscillations in Vacuum

In the context of a type I seesaw scenario which leads to get light left-handed and heavy right-handed Majorana neutrinos, we obtain expressions for the transition probability densities between two flavor neutrinos in the cases of left-handed and right-handed neutrinos. We obtain these expressions in the context of an approach developed in the canonical formalism of Quantum Field Theory for neutrinos which are considered as superpositions of mass-eigenstate plane waves with specific momenta. The expressions obtained for the left-handed neutrino case after the ultra-relativistic limit is taking lead to the standard probability densities which describe light neutrino oscillations. For the right-handed neutrino case, the expressions describing heavy neutrino oscillations in the non-relativistic limit are different respect to the ones of the standard neutrino oscillations. However, the right-handed neutrino oscillations are phenomenologically restricted as is shown when the propagation of heavy neutrinos is considered as superpositions of mass-eigenstate wave packets.

Leptogenesis as a common origin for matter and dark matter

We propose a model of asymmetric dark matter (DM) where the dark sector is an identical copy of both forces and matter of the standard model (SM) as in the mirror universe models discussed in literature. In addition to being connected by gravity, the SM and DM sectors are also connected at high temperature by a common set of heavy right-handed Majorana neutrinos via their Yukawa couplings to leptons and Higgs bosons. The lightest nucleon in the dark (mirror) sector is a candidate for dark matter. The out of equilibrium decay of right-handed neutrino produces equal lepton asymmetry in both sectors via resonant leptogenesis which then get converted to baryonic and dark baryonic matter. The dark baryon asymmetry due to higher dark nucleon masses leads to higher dark matter density compared to the familiar baryon density that is observed. The standard model neutrinos in this case acquire masses from the inverse seesaw mechanism. A kinetic mixing between the U(1) gauge fields of the two sectors is introduced to guarantee the success of Big-Bang Nucleosynthesis.

The minimal seesaw model at the TeV scale

We point out that the minimal seesaw model can provide a natural framework to accommodate tiny neutrino masses, while its experimental testability and notable predictiveness are still maintained. This possibility is based on the observation that two heavy right-handed Majorana neutrinos in the minimal seesaw model may naturally emerge as a pseudo-Dirac fermion. In a specific scenario, we show that the tri-bimaximal neutrino mixing can be produced, and only the inverted neutrino mass hierarchy is allowed. The low-energy phenomena, including non-unitarity effects in neutrino oscillations, neutrinoless double-beta decays and rare lepton-flavor-violating decays of charged leptons ℓα→ℓβγ, have been explored. The collider signatures of the heavy singlet neutrino are also briefly discussed.

Charged lepton flavour violating radiative decays ℓ i → ℓ j + γ in see-saw models with A 4 symmetry

The charged lepton flavour violating (LFV) radiative decays, $\mu\to e+\gamma$, $\tau\to \mu+\gamma$ and $\tau\to e +\gamma$ are investigated in a class of supersymmetric $A_4$ models with three heavy right-handed (RH) Majorana neutrinos, in which the lepton (neutrino) mixing is predicted to leading order (LO) to be tri-bimaximal. The light neutrino masses are generated via the type I see-saw mechanism. The analysis is done within the framework of the minimal supergravity (mSUGRA) scenario, which provides flavour universal boundary conditions at the scale of grand unification $M_X \approx 2 \times 10^{16}$ GeV. Detailed predictions for the rates of the three LFV decays are obtained in two explicit realisations of the $A_4$ models due to Altarelli and Feruglio and Altarelli and Meloni, respectively.

On the interplay between ‘high’ and ‘low’ energy CP violation in flavoured leptogenesis

The possible interplay in ‘flavoured’ leptogenesis between the ‘low energy’ CP violation originating from the PMNS neutrino mixing matrix U, and the ‘high energy’ CP-violation which can be present in the matrix of neutrino Yukawa couplings, λ, and can manifest itself only in ‘high’ energy scale processes, is discussed. The results reported are obtained for type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum. It is shown that in the case of inverted hierarchical light neutrino mass spectrum, there exist regions in the corresponding leptogenesis parameter space where the relevant ‘high energy’ phases have large CP-violating values, but the purely ‘high energy’ contribution in Yb plays a sub-dominant role in the production of baryon asymmetry compatible with the observations.

CP violation and lightest neutrino mass effects in thermal leptogenesis

Effects of the lightest neutrino mass in ‘flavoured’ leptogenesis when the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana phases in the neutrino mixing matrix U are discussed. The type I see-saw scenario with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The ‘orthogonal’ parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. Results for light neutrino mass spectrum with normal and inverted ordering (hierarchy) are reviewed.

The interplay between “low” and “high” energy CP-violation in leptogenesis

We analyse, within the “flavoured” leptogenesis scenario of baryon asymmetry generation, the interplay of “low energy” CP-violation, originating from the PMNS neutrino mixing matrix U, and “high energy” CP-violation, which can be present in the matrix of neutrino Yukawa couplings, λ, and can manifest itself only in “high” energy scale processes. The type I see-saw model with three heavy right-handed Majorana neutrinos having a hierarchical spectrum is considered. The “orthogonal” parameterisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. In this approach the matrix R is the source of “high energy” CP-violation. Results for normal hierarchical (NH) and inverted hierarchical (IH) light neutrino mass spectrum are derived in the case of decoupling of the heaviest right-handed Majorana neutrino. It is shown that taking into account the contribution to Y B due to the CP-violating phases in the neutrino mixing matrix U can change drastically the predictions for Y B , obtained assuming that only “high energy” CP-violation from the R-matrix is operative in leptogenesis. In the case of the IH spectrum, in particular, there exist significant regions in the corresponding parameter space where the purely “high energy” contribution in Y B plays a subdominant role in the production of baryon asymmetry compatible with the observations.

On the “Low” and “High” Energy CP Violation in Leptogenesis

The CP violation necessary for the generation of the baryon asymmetry of the Universe YB in the “flavoured” leptogenesis scenario, based on the simplest type I see-saw model of ν -mass generation, can arise from the “low energy” neutrino mixing matrix U and/or from the “high energy” part of neutrino Yukawa couplings. The latter can mediate CP-violating phenomena only at some high energy scale. We review briefly some of the results on the the interplay between the contributions in Y B due to these two sources of CP violation in thermal leptogenesis with three heavy right-handed Majorana neutrinos having hierarchical mass spectrum.

A case of subdominant/suppressed “high energy” contribution to the baryon asymmetry of the Universe in flavoured leptogenesis

The CP-violation necessary for the generation of the baryon asymmetry of the Universe YB in the “flavoured” leptogenesis scenario can arise from the “low energy” PMNS neutrino mixing matrix U and/or from the “high energy” part of neutrino Yukawa couplings, which can mediate CP-violating phenomena only at some high energy scale. The possible interplay between these two types of CP-violation is analysed. The type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. We show that in the case of inverted hierarchical light neutrino mass spectrum, there exist regions in the corresponding leptogenesis parameter space where the relevant “high energy” phases have large CP-violating values, but the purely “high energy” contribution in YB plays a subdominant role in the production of baryon asymmetry compatible with the observations. In some of these regions the purely “high energy” contribution in YB is so strongly suppressed that one can have successful leptogenesis only if the requisite CP-violation is provided by the Majorana phase(s) in the neutrino mixing matrix.

Probing the reheating temperature at colliders and with primordial nucleosynthesis

Considering gravitino dark matter scenarios with a long-lived charged slepton, we show that collider measurements of the slepton mass and its lifetime can probe not only the gravitino mass but also the post-inflationary reheating temperature TR. In a model independent way, we derive upper limits on TR and discuss them in light of the constraints from the primordial catalysis of 6Li through bound-state effects. In the collider-friendly region of slepton masses below 1 TeV, the obtained conservative estimate of the maximum reheating temperature is about TR=3×109 GeV for the limiting case of a small gluino–slepton mass splitting and about TR=108 GeV for the case that is typical for universal soft supersymmetry breaking parameters at the scale of grand unification. We find that a determination of the gluino–slepton mass ratio at the Large Hadron Collider will test the possibility of TR>109 GeV and thereby the viability of thermal leptogenesis with hierarchical heavy right-handed Majorana neutrinos.

THE MINIMAL TYPE-II SEESAW MODEL AND FLAVOR-DEPENDENT LEPTOGENESIS

Current experimental data allow the zero value for one neutrino mass, either m1 = 0 or m3 = 0. This observation implies that a realistic neutrino mass texture can be established by starting from the limit (a) m1 = m2 = 0 and m3 ≠ 0 or (b) m1 = m2 ≠ 0 and m3 = 0. In both cases, we may introduce a particular perturbation which ensures the resultant neutrino mixing matrix to be the tri-bimaximal mixing pattern or its viable variations. We find that it is natural to incorporate this kind of neutrino mass matrix in the minimal Type-II seesaw model with only one heavy right-handed Majorana neutrino N. We show that it is possible to account for the cosmological baryon number asymmetry in the m3 = 0 case via thermal leptogenesis, in which the CP-violating asymmetry of N decays is attributed to the electron flavor.

Massive and massless neutrinos on unbalanced seesaws**Supported by National Natural Science Foundation of China (10425522)

The observation of neutrino oscillations requires new physics beyond the standard model (SM). A SM-like gauge theory with p lepton families can be extended by introducing q heavy right-handed Majorana neutrinos but preserving its SU(2)L×U(1)Y gauge symmetry. The overall neutrino mass matrix M turns out to be a symmetric (p+q)×(p+q) matrix. Given p>q, the rank of M is in general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The existence of (p-q) massless left-handed Majorana neutrinos is an exact consequence of the model, independent of the usual approximation made in deriving the Type-I seesaw relation between the effective p×p light Majorana neutrino mass matrix Mν and the q×q heavy Majorana neutrino mass matrix MR. In other words, the numbers of massive left- and right-handed neutrinos are fairly matched. A good example to illustrate this ``seesaw fair play rule'' is the minimal seesaw model with p=3 and q=2, in which one massless neutrino sits on the unbalanced seesaw.

Effects of lightest neutrino mass in leptogenesis

The effects of the lightest neutrino mass in “flavoured” leptogenesis are investigated in the case when the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana phases in the neutrino mixing matrix U. The type I see-saw scenario with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The “orthogonal” parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. Results for light neutrino mass spectrum with normal and inverted ordering (hierarchy) are obtained. It is shown, in particular, that if the matrix R is real and CP-conserving and the lightest neutrino mass m 3 in the case of inverted hierarchical spectrum lies the interval 5 × 10 −4 eV ≲ m 3 ≲ 7 × 10 −3 eV , the predicted baryon asymmetry can be larger by a factor of ∼100 than the asymmetry corresponding to negligible m 3 ≅ 0 . As consequence, we can have successful thermal leptogenesis for 5 × 10 −6 eV ≲ m 3 ≲ 5 × 10 −2 eV even if R is real and the only source of CP-violation in leptogenesis is the Majorana and/or Dirac phase(s) in U.

Deviations from tribimaximal neutrino mixing in the type-II seesaw model and leptogenesis

Current experimental data allow the zero value for one neutrino mass, either m(1)=0 or m(3)=0. This observation implies that a realistic neutrino mass texture can be established by starting from the limit (a) m(1)=m(2)=0 and m(3)not equal 0 or (b) m(1)=m(2)not equal 0 and m(3)=0. In both cases, we may introduce a particular perturbation which ensures the resultant neutrino mixing matrix to be the tribimaximal mixing pattern or its viable variations with all entries being formed from small integers and their square roots. We find that it is natural to incorporate this kind of neutrino mass matrix in the minimal type-II seesaw model with only one heavy right-handed Majorana neutrino N in addition to the SU(2)(L) Higgs triplet Delta(L). We show that it is possible to account for the cosmological baryon number asymmetry in the m(3)=0 case via thermal leptogenesis, in which the one-loop vertex correction to N decays is mediated by Delta(L) and the CP-violating asymmetry of N decays is attributed to the electron flavor.

GENERALIZED FUKUGITA–TANIMOTO–YANAGIDA NEUTRINO MASS ANSATZ

We generalize the Fukugita–Tanimoto–Yanagida ansatz by allowing the masses of three heavy right-handed Majorana neutrinos, Mi (i = 1,2,3), to be partially non-degenerate and search for the parameter space which can be consistent with the current neutrino oscillation data, for three non-degenerate mass cases (A) M3 = M2 ≠ M1, (B) M2 = M1 ≠ M3 and (C) M1 = M3 ≠ M2. We also examine the effect of the deviation from the complete mass degeneracy in each case. Finally, we obtain the numerical constraints on three light neutrino masses, three neutrino mixing angles and three CP-violating phases, together with the predictions for the Jarlskog invariant of CP violation and the effective masses of the tritium beta decay and the neutrinoless double-beta decay.

Duality in left-right symmetric seesaw

A reconstruction of the mass matrix of heavy right-handed Majorana neutrinos is performed in the framework of the left-right symmetric type I+II seesaw mechanism. An intriguing pairwise duality relation between different solutions is shown to exist.

NEUTRINO MASSES, LEPTON FLAVOR MIXING AND LEPTOGENESIS IN THE MINIMAL SEESAW MODEL

We present a review of neutrino phenomenology in the minimal seesaw model (MSM), an economical and intriguing extension of the Standard Model with only two heavy right-handed Majorana neutrinos. Given current neutrino oscillation data, the MSM can predict the neutrino mass spectrum and constrain the effective masses of the tritium beta decay and the neutrinoless double-beta decay. We outline five distinct schemes to parameterize the neutrino Yukawa-coupling matrix of the MSM. The lepton flavor mixing and baryogenesis via leptogenesis are investigated in some detail by taking account of possible texture zeros of the Dirac neutrino mass matrix. We derive an upper bound on the CP-violating asymmetry in the decay of the lighter right-handed Majorana neutrino. The effects of the renormalization-group evolution on the neutrino mixing parameters are analyzed, and the correlation between the CP-violating phenomena at low and high energies is highlighted. We show that the observed matter-antimatter asymmetry of the Universe can naturally be interpreted through the resonant leptogenesis mechanism at the TeV scale. The lepton-flavor-violating rare decays, such as μ→e+γ, are also discussed in the supersymmetric extension of the MSM.

Lepton flavor violating decays as probes of neutrino mass spectra and heavy Majorana neutrino masses

We investigate the lepton flavor violating (LFV) rare decays in the supersymmetric minimal seesaw model in which the Frampton-Glashow-Yanagida ansatz is incorporated. The branching ratio of mu -> e gamma is calculated in terms of the snowmass points and slopes (SPS). We find that the inverted mass hierarchy is disfavored by all SPS points. In addition, once the ratio of BR(tau ->mu gamma) to BR(mu -> e gamma) is measured, one may distinguish the normal and inverted neutrino mass hierarchies, and confirm the masses of heavy right-handed Majorana neutrinos by means of the LFV processes and the thermal leptogenesis mechanism. It is worthwhile to stress that this conclusion is independent of the supersymmetric parameters.

Detection of heavy Majorana neutrinos and right-handed bosons

The SU c (3) ⊗ SU L (2) ⊗ SU R (2) ⊗ U(1) left-right (LR) symmetric model explains the origin of the parity violation in weak interactions and predicts the existence of additional gauge bosons W R and Z′. In addition, heavy right-handed Majorana neutrino states N arise naturally within the LR symmetric model. The states N could be partners of light neutrino states, related to their nonzero masses through the seesaw mechanism. This makes the searches for W R , Z′, and N interesting and important. In the framework of the minimal LR model, we study the possibility to observe signals from N and W R production in pp collisions after three years of running at low LHC luminosity. We show that their decay signals can be identified with a small background, especially in the case of same-sign leptons in the final state. For the integral LHC luminosity of L t = 30 fb−1, the 5σ discovery of W R boson and heavy Majorana neutrinos N e with masses \(M_{W_R } \) up to 4 TeV and \(M_{N_e } \) up to 2.4 TeV, respectively, is found to be possible.

Seesaw mechanism, Majorana CP-violation, μ→eγ decay, leptogenesis and (ββ)0ν-decay

We discuss the lepton flavour violating μ decays, μ→e+γ, etc and thermal leptogenesis in the minimal supersymmetric standard model with flavour universal soft supersymmetry breaking at the cutoff scale and seesaw mechanism with heavy right-handed Majorana neutrinos with hierarchical spectrum of masses, M1≪M2≪M3. For a typical value of the heaviest right-handed Majorana neutrino mass, M3≳5×1013 GeV, and supersymmetry particle masses in the few 100 GeV range, the predicted μ→e+γ decay rate exceeds by few order of magnitude the present experimental upper limit. This problem is avoided if the matrix of neutrino Yukawa couplings has a specific form. The latter leads to a correlation between the baryon asymmetry of the Universe predicted by leptogenesis, BR(μ→e+γ) and the effective Majorana mass in neutrinoless double beta decay.