Right-handed Majorana Neutrino Mass Research Articles

Explicit SO(10) supersymmetric grand unified model for the higgs and yukawa sectors

A complete set of fermion and Higgs superfields is introduced with well-defined SO(10) properties and U(1)xZ2xZ2 family charges from which the Higgs and Yukawa superpotentials are constructed. The structures derived for the four Dirac fermion and right-handed Majorana neutrino mass matrices coincide with those previously obtained from an effective operator approach. Ten mass matrix input parameters accurately yield the twenty masses and mixings of the quarks and leptons with the bimaximal atmospheric and solar neutrino vacuum solutions favored in this simplest version.

NEUTRINO MASSES AND MIXINGS IN SO(10)M

Assuming a Zee-like matrix for the right-handed neutrino Majorana masses in the seesaw mechanism, one gets maximal mixing for vacuum solar oscillations, a very small value for Ue3 and an approximate degeneracy for the two lower neutrino masses. The scale of right-handed neutrino Majorana masses is in good agreement with the value expected in an SO (10)M model with Pati–Salam SU (4)× SU (2)× SU (2) intermediate symmetry.

Neutrino masses and mixings in SO(10)

Assuming a Zee-like matrix for the right-handed neutrino Majorana masses in the see-saw mechanism, one gets maximal mixing for vacuum solar oscillations, a very small value for $U_{e3}$ and an approximate degeneracy for the two lower neutrino masses. The scale of right-handed neutrino Majorana masses is in good agreement with the value expected in a SO(10) model with Pati-Salam $SU(4)\ts SU(2)\ts SU(2)$ intermediate symmetry.

Four light neutrinos in the singular seesaw mechanism with Abelian flavor symmetry

The four light neutrino scenario, which explains the atmosphere, solar and LSND neutrino experiments, is studied in the framework of the seesaw mechanism. By taking both the Dirac and Majorana mass matrices of neutrinos to be singular, the four neutrino mass spectrum consisting of two almost degenerate pairs separated by a mass gap $\ensuremath{\sim}1 \mathrm{eV}$ is naturally generated. Moreover, the right-handed neutrino Majorana mass can be at the $\ensuremath{\sim}{10}^{14} \mathrm{GeV}\mathrm{}$ scale unlike in the usual singular seesaw mechanism. Abelian flavor symmetry is used to produce the required neutrino mass pattern. A specific example of the flavor charge assignment is provided to show that maximal mixings between the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{-}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ and ${\ensuremath{\nu}}_{e}\ensuremath{-}{\ensuremath{\nu}}_{s}$ are respectively attributed to the atmosphere and solar neutrino anomalies while small mixing between two pairs to the LSND results. The implications to the other fermion masses are also discussed.

Large Majorana Mass from the Anomalous U(1) Gauge Symmetry

We show a new and simple model which induces large Majorana masses of right-handed neutrinos. It is based on U(1)_X anomalous gauge symmetry, which is cancelled by the Green-Schwarz mechanism. These Majorana masses can solve the solar neutrino problem by the vacuum oscillation mechanism. The superpotential of this model is scale invariant. The field contents are simple extensions of the MSSM, which have four standard gauge singlet fields, two extra vector-like fields, and right-handed neutrinos in addition to the MSSM.

Quadruple Yukawa unification in the minimal supersymmetric standard model

Predictions for m 1, tan β, m ν τ are calculated for quadruple third family t- b- τ- ν t Yukawa unified models in the MSSM. The renormalisation group equations for the 3 families of the MSSM, including the right-handed neutrino, are presented. For right-handed tau neutrino Majorana masses that are bigger than 10 11 GeV, the tau neutrino mass is consistent with present cosmological bounds. The m t , tan β predictions are approximately equivalent to those in triple third family Yukawa unified models.

How Can We Obtain a Large Majorana-Mass in Calabi-Yau Models?

In a certain type of Calabi-Yau superstring models it is clarified that the symmetry breaking occurs by stages at two large intermediate energy scales and that two large intermediate scales induce large Majorana-masses of right-handed neutrinos. Peculiar structure of the effective nonrenormalizable interactions is crucial in the models. In this scheme Majorana-masses possibly amount to O(109 ∼10 GeV) and see-saw mechanism is at work for neutrinos. Based on this scheme we propose a viable model which explains the smallness of masses for three kinds of neutrino νe, νµ and ντ. Special forms of the nonrenormalizable interactions can be understood as a consequence of an appropriate discrete symmetry of the compactified manifold.

How Can We Obtain a Large Majorana-Mass in Calabi-Yau Models?

In a certain type of Calabi-Yau superstring models it is clarified that the symmetry breaking occurs by stages at two large intermediate energy scales and that two large intermediate scales induce large Majorana-masses of right-handed neutrinos. Peculiar structure of the effective nonrenormalizable interactions is crucial in the models. In this scheme Majorana-masses possibly amount to $O(10^{9 \sim 10}\gev)$ and see-saw mechanism is at work for neutrinos. Based on this scheme we propose a viable model which explains the smallness of masses for three kind of neutrinos $\nu _e, \nu _{\mu} \ {\rm and}\ \nu _{\tau}$. Special forms of the nonrenormalizable interactions can be understood as a consequence of an appropriate discrete symmetry of the compactified manifold.

NEUTRINO OSCILLATION AND LEPTON MASS MATRIX

We apply the empirical quark mass matrices to the lepton sector and study the solar neutrino problem and the atmospheric vμ deficit problem simultaneously. We show that their consistent explanation is possible on the basis of these matrices. The lepton sector mass matrices need the phase structure which is different from the ones of the quark sector. However, even if the phase structure of the mass matrices is identical in both sectors, an interesting suppression mechanism of sin 2 2θ12 which is related to the solar neutrino problem can be induced from the right-handed neutrino Majorana mass matrix. We discuss such a possibility through the concrete examples.

Seesaw enhancement of lepton mixing.

The see-saw mechanism of neutrino mass generation may enhance lepton mixing up to maximal even if the Dirac mass matrices of leptons have structure similar to that in the quark sector. Two sets of conditions for such an enhancement are found. The first one includes the see-saw generation of heavy Majorana masses for right-handed neutrinos and a universality of Yukawa couplings which can follow from the unification of neutrinos with new superheavy neutral leptons. The second set is related to lepton number symmetry of the Yukawa interactions in the Dirac basis of neutrinos. Models which realize these conditions have strong hierarchy or strong degeneration of Majorana masses of the right-handed neutrinos.

Phenomenology of superstring-inspired SO(10) grand-unified-theory model with intermediate scale.

We examine in detail a superstring-inspired SO(10) grand-unified-theory model in which the mixing of Weinberg-Salam Higgs fields and large Majorana masses for right-handed neutrinos are generated by the higher-dimensional terms in the superpotential at the intermediate-scale symmetry breaking. Fixing the Higgs-field mixing strength $\ensuremath{\mu}$ as 1 TeV and assuming the usual soft terms of broken $N=1$ supergravity, we study the radiative symmetry breakings at the intermediate scale ${M}_{I}$ and the scale ${M}_{W}$. Conditions and constraints for the symmetry breakings severely restrict the allowed range of the supergravity parameters and give bounds on the top-quark mass ${m}_{t}$. We have obtained ${m}_{t}\ensuremath{\le}141$ GeV if the identity $B=A\ensuremath{-}1$ is assumed. The low-energy particle spectra are analyzed. All squarks and sleptons are predicted to have masses in the TeV region. Some of the gaugino-related supersymmetric particles can be light, and lower bounds for these sparticle masses are given. One neutral Higgs boson is light and the other Higgs bosons are all very massive (g a few TeV).

Limits on left-right mixing in weak interactions

The possible occurrence of large Majorana masses for right-handed neutrinos vitiates previous limits on the mixing between left- and right-handed gauge bosons in symmetrical models of weak interactions. New limits are obtained, resting either on deep inelastic inclusive antineutrino scattering, or on ΔI = 3 2 contributions to nonleptonic decays.

Nucleon Decay in Supergrand Unification

Grand unifications of electroweak and strong interactions have been realized originally by the SU(5) u and more elegantly by the SO (10) model. 21 The SO (10) models are left-right symmetric and therefore aesthetically more appealing than the original SU(5) model. However, they are essentially single-family theories and the generation structure is only put in by hand. The further step toward a complete unification is required to construct a larger gauge group G including the family degrees of freedom, such that G~G0 xG1 with G 0 being S0(10) and G1 so-called horizontal symmetry. 31 In such supergrand unified theories, a 126 Higgs scalar of SO (10) with a suitable horizontal quantum number produces huge Majorana masses of right-handed neutrinos. A mass matrix of neutral leptons is given by41