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R. N. Mohapatra

Publications and source records attributed to R. N. Mohapatra.

At least 217 records · Page 12Linked to original sources
arXiv1995

Intermediate Scales in SUSY SO(10), b-τunification and Hot Dark Matter Neutrinos

Considerations of massive neutrinos, baryogenesis as well as fermion mass textures in the grand unified theory framework provide strong motivations for supersymmetric(SUSY) SO(10) as the theory beyond the standard model. If one wants to simultaneously solve the strong CP problem via the Peccei-Quinn mechanism, the most natural way to implement it within the framework of the SUSY SO(10) model is to have an intermediate scale ($v_{BL}$) (corresponding to B-L symmetry breaking) around the invisible axion scale of about 10$^{11}$ - 10$^{12}$ GeV. Such a scale is also desirable if $ν_τ$ is to constitute the hot dark matter (HDM) of the universe. In this paper, we discuss examples of superstring inspired SUSY SO(10) models with intermediate scales that are consistent with the low energy precision measurements of the standard model gauge couplings. The hypothesis of $b-τ$ unification which is a successful prediction of many grand unified theories is then required of these models and the resulting prediction of $b$-quark mass is used as a measure of viability of these schemes. Detailed analysis of a model with a $v_{BL}\simeq 10^{11}$ GeV, which satisfies both the requirements of invisible axion and $ν_τ$ as HDM is presented and shown to lead to $m_b\simeq 4.9$ GeV in the one-loop approximation.

hep-ph↗
arXiv1995

Multi-Majoron Modes for Neutrinoless Double-Beta Decay

We construct two new classes of models for double beta decay, each of which leads to an electron spectrum which differs from the decays which are usually considered. One of the classes has a spectrum which has not been considered to date, and which is softer than the usual two-neutrino decay of the Standard Model. We construct illustrative models to show how other phenomenological bounds can be accommodated. We typically find that, although all other bounds can be satisfied, the predicted double-beta decay rate only in one class of these models is at best large enough to be just detectable in current experiments.

hep-ph↗
arXiv1994

Almost Degenerate Neutrinos with Maximal Mixing

If the upper limit on the effective (Majorana) neutrino mass from neutrinoless double beta decay experiments is confirmed to be much less than an electron-volt, then one way to reconcile it with the degenerate neutrino mass pattern suggested recently to explain the observed deficit of solar and atmospheric neutrinos as well as neutrinos as HDM is to postulate that there be maximal mixing among the three light (or two) neutrinos. This suggestion is advanced in this paper and is analysed.

hep-ph↗
arXiv1994

Mass Matrix Textures From Superstring Inspired SO(10) Models

We give a general prescription for deriving quark and lepton mass matrices with ``texture'' zeros in the framework of superstring inspired $SO(10)$ models. The key to our approach is a new way to naturally implement the doublet--triplet splitting which enables us to obtain symmetric quark and lepton mass matrices which have different structures in the up and the down quark sectors. We illustrate our method by deriving the Georgi--Jarlskog texture which has six predictions in the flavor sector, and then show how it generalizes to other symmetric texture models.

hep-ph↗
arXiv1994

Heavy Sterile Neutrinos and Neutrinoless Double Beta Decay

We investigate the possibility of producing neutrinoless double beta decay without having an electron neutrino with a mass in the vicinity of 1 eV. We do so by having a much lighter electron neutrino mix with a much heavier (m > 1 GeV) sterile neutrino. We study the constraints on the masses and mixings of such heavy sterile neutrinos from existing laboratory, astrophysical and cosmological information, and discuss the properties it would require in order to produce a detectable signal in current searches for neutrinoless double beta decay.

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arXiv1994

Implications of a Purely Right-Handed Bottom Quark Decay Coupling

We examine the implications of the hypothesis that the decays of the b-quark occur via pure right-handed couplings. We show that the existing lower limits on neutrinoless double beta decay imply that any gauge model realizing this idea must have either an $L_e-L_μ$ or $L_e-L_τ$ symmetry. We then show that constraints of cosmology together with observations from SN1987A imply that the right-handed neutrinos in this model must be heavier than about 100 MeV in general. In one special case with the $L_e-L_μ$ symmetry, the $ν_{τ_R}$ is heavier than 2 GeV so that this particular version of the model is already ruled out.

hep-ph↗
arXiv1994

Constraints on Massive Tau Neutrinos and their Cosmological Implications

We point out the following astrophysical consequences of a tau neutrino with mass in the MeV range: (i) if it has a small electric charge which will allow it to become a cold dark matter of the universe, then present limits on the 511 KeV gamma ray line rule out the possibility that it contributes an $Ω_{ν_τ}$ between .1 to 1 making it unsuitable as a cold dark matter candidate; (ii) if an electrically neutral MeV range $ν_τ$ decays to $ν_e + χ$ ( where $χ$ is a massless boson) , then its lifetime is bounded by SN1987A observations to be within a window $.05~~sec.\leq τ(ν_τ)~\leq 300~sec./(m_{ν_τ}~in~ MeV)$ a range which may be of interest from the point of view of structure formation. Encouraged by the overlap between the range allowed in (ii) above and that required for a proposed structure formation mechanism by Dodelson et al., we search for simple extensions of the standard model, where such masses and lifetimes may arise for natural values of parameters and show that the already existing singlet majoron and low scale left-right models have this property. We also comment on possible familon models for this decay.

hep-ph↗
arXiv1994

Automatically R-Conserving SUSY SO(10) Models and Mixed Light Higgs Doublets

In automatic R-parity conserving SO(10) models, the simplest way to accomodate realistic fermion masses is to demand that that the light Higgs doublets be linear combinations of the {10} and {126}-bar grand unified Higgs representations. We study the realization of this mixed light Higgs property consistent with doublet-triplet splitting in a minimal model and discuss its predictions for neutrino masses and implications for proton decay.

hep-ph↗
arXiv1994

Hints of Grand Unification in Neutrino Data

There are strong indications for neutrino masses and mixings in the data on solar neutrinos, the observed deficit of the muon neutrinos from the atmosphere as well as the discussions of the dark matter of the universe after COBE data. It is argued that the SO(10) grand unified has the right symmetry breaking properties as dictated by LEP data to accomodate the neutrino masses and mixings suggested by these experiments. Predictions for neutrino masses in two different versions of the model are discussed.

hep-ph↗
arXiv1994

Understanding the Standard Model

We explore to what extent the various assumptions behind the standard model as well as the observed quantization of electric charges of quarks and leptons can be understood using the Adler-Bell-Jackiw anomalies. The effect of including a non-zero neutrino mass on these considerations is also discussed.

hep-ph↗
arXiv1994

A Single Scale Theory for Cold and Hot Dark Matter

We show that a recently proposed extension of the MSSM can provide a scenario where both the cold and hot dark matter of the universe owe their origin to a single scale connected with the breakdown of the global B-L symmetry. The susy partner of the majoron and the light Majorana neutrinos are the cold and hot dark matter candidates respectively in this model and their desired relative abundances emerge when the scale of B-L symmetry breaking is in the TeV range.

hep-ph↗
arXiv1994

An SO(10)XS-4 Scenario for Naturally Degenerate Neutrinos

The simplest scenario for the three known light neutrinos that fits the solar and atmospheric neutrino deficit and a mixed dark matter (MDM) picture of the universe requires them to be highly degenerate with $m_ν \sim$ 1 - 2 eV. We propose an SO(10) grand unified model with an S$_{4}$-horizontal symmetry that leads naturally to such a scenario. An explicit numerical analysis of the quark and lepton sector of the model shows that it can lead to desired mass differences to fit all data only for the small angle non-adiabatic MSW solution to the solar neutrino puzzle.

hep-ph↗
arXiv1993

Natural Doublet-Triplet Splitting in Supersymmetric SO(10) Model

We construct a supersymmetric SO(10) model, where natural doublet-triplet splitting implemented via the Dimopoulos-Wilczek mechanism is stable under the addition of 126+\bar{126} Higgs superfields needed to generate the small neutrino masses via the see-saw mechanism and where both the charged fermion and neutrino masses arise from just one set of 10 and \bar{126} multiplets.

hep-ph↗
arXiv1993

Effects of $e^- e^+ ν_e$ 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 $ν_τ$ decaying into the visible channel $ν_τ\rightarrow e^+ e^- ν_e$, 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" $ν_τ$'s and spin allignment possibility in the supernova.

hep-ph↗
arXiv1993

Minimal SO(10) Grand Unification: Predictions for Proton Decay and Neutrino Masses and Mixings:

Prospects for SO(10) as a minimal grand unification group have recently been heightened by several considerations such as the MSW resolution of the solar neutrino puzzle, baryogenesis, possibility for understanding fermion masses etc. I review the present status of the minimal SO(10) models with special emphasis on the predictions for proton lifetime and predictions for neutrino masses for the non-supersymmetric case and discuss some preliminary results for the supersymmetric case. It was generally believed that minimal SO(10) models predict wrong mass relations between the charged fermions of the first and second generations; furthermore, while the smallness of the neutrino masses in these models arises from the see-saw mechanism, it used to be thought that detailed predictions for neutrino masses and mixings require further adhoc assumptions. In this talk, I report some recent work with K.S.Babu, where we discovered that the minimal SO(10) model, both with and without SUSY, has in it a built-in mechanism that not only corrects the bad mass relations between the charged fermions but at the same time allows a complete prediction for the masses and mixings in the neutrino sector. We define our minimal model as the one that consists of the smallest set of Higgs multiplets that are needed for gauge symmetry breaking. Our result is based on the hypothesis that the complex {\bf 10} of Higgs bosons has only a single coupling to the fermions. This hypothesis is guaranteed in supersymmetric models and in non-SUSY models that obey a softly broken Peccei-Quinn symmetry.

hep-ph↗
arXiv1993

Lepton Flavor Violation and the Tau Neutrino Mass

We point out that, in the left-right symmetric model of weak interaction, if $ν_τ$ mass is in the keV to MeV range, there is a strong correlation between rare decays such as $τ\rightarrow 3 μ, τ\rightarrow 3 e$ and the $ν_τ$ mass. In particular, we point out that a large range of $ν_τ$ masses are forbidden by the cosmological constraints on $m_{ν_τ}$ in combination with the present upper limits on these processes.

hep-ph↗
arXiv1993

Cosmological Constraint on the Scale of the Supersymmetric Singlet Majoron

In a SUSY theory with a spontaneously broken global symmetry, G, if the scale of SUSY breaking, $M_s$ is smaller than the scale $M_G$ of the global symmetry, the Nambu-Goldstone boson, $χ$ is accompanied by two massive superpartners ( a fermionic, $Ψ_χ$ and a scalar $σ_χ$) with mass of order $M_s$. Cosmological considerations imply stringent constraints on the couplings of $Ψ_χ$ and $σ_χ$. Application of these considerations to the supersymmetric singlet Majoron model leads to an upper limit on the scale $V_{BL}$ of global $U(1)_{B-L}$ symmetry to be less than $10^4 GeV$, for resonable values of parameters in the theory.

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