arXiv subjects

R. N. Mohapatra

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

At least 199 records · Page 11Linked to original sources

arXiv1997

New Messenger Sector for Gauge Mediated Supersymmetry Breaking

We propose a new class of gauge mediated supersymmetry breaking models where the standard model gauge group is embedded into the gauge group $SU(2)_L\times U(1)_{I_{3R}}\times U(1)_{B-L}$ [or $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$] at the supersymmetry breaking scale $Λ_S$. The messenger sector in these models can consist of color singlet but $U(1)_{I_{3R}}$ and $U(1)_{B-L}$ nonsinglet fields. The distinguishing feature of these models are (i)exact R-parity conservation, (ii) nonvanishing neutrino masses and (iii) a unified hidden and messenger sector potential. The simplest version of these models predicts the existence of light gluinos which can however be made heavier by a simple modification of the supersymmetry breaking sector.

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arXiv1997

Explaining the HERA Anomaly Without Giving Up R-parity Conservation

We point out that in extended supersymmetric models such as supersymmetric left-right models, it is possible to have leptoquarks that explain the HERA high $Q^2$ anomaly without giving up R-parity conservation. The leptoquarks belong to vectorlike $(2, 2, \pm{4/3}, 3 or 3^*) $ representations of $SU(2)_L\times SU(2)_R\times U(1)_{B-L}\times SU(3)_c$ (denoted $G_{2213}$). Unlike the R-parity violating scenario, the leptoquarks are accompanied by new superpartners,the leptoquarkino which leads to many intersting signatures in other collider experiments. At Tevatron, pair productions of the leptoquarkino will give rise to dilepton signals very distinct from the top productions. These models can lead to unification of gauge coupling constants at a scale of around $10^{10}$ GeV implying that grand unification group is not of the usual SU(5) or SO(10) types but rather an automatically R-parity conserving $SU(5)\times SU(5)$ GUT model recently proposed by one of the authors (R. N. M.) which leads to a stable proton.

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arXiv1997

Neutrino Mass Textures and the Nature of New Physics Implied by Present Neutrino Data

If all indications for neutrino oscillations observed in the solar, atmospheric neutrino data as well as in the LSND experiments are borne out by the ongoing and future experiments, then they severely constrain the neutrino mass texture. In particular, the need for an ultralight sterile neutrino is hard to avoid. Such ultralight neutrinos have profound implications not only for physics beyond the standard model but also perhaps for physics beyond the conventional grand unification. We discuss a scenario involving a parallel universe that interacts with the familiar universe only via gravitational interactions, where the ultralightness of the sterile neutrino follows from the same physics that explains the near masslessness of the familiar neutrinos.

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arXiv1996

New Astrophysical Constraints on the Mass of the Superlight Gravitino

In some supergravity models, the superlight gravitino is accompanied by a light weakly coupled scalar (S) and pseudo-scalar (P) particle. The coupling of these particles to matter is inversely proportional to the product of the gravitino mass and the Planck mass. As a result, their emission from the stars and supernovae via the photon electron scattering reaction for certain ranges of the gravitino mass can become the dominant energy loss mechanism in contradiction with observations thereby ruling out those mass values for the gravitino. For scalar and/or pseudo-scalar masses between 10 MeV and a keV, the SN1987A observations exclude the gravitino mass range from 0.03 eV to 30 eV whereas if the S/P masses are less than a keV, constraints of stellar energy loss can exclude the gravitino masses ranging from $3\times 10^{-6}$ eV to 50 eV for the photino mass of 100 GeV. We also find that for S/P mass less than an MeV, Big Bang Nucleosynthesis constraints imply a gravitino mass larger than one eV. These are the most stringent bounds to date on the gravitino mass in this class of models.

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arXiv1996

Supersymmetric models with anomalous U(1) mediated supersymmetry breaking

We construct realistic supergravity models where supersymmetry breaking arises from the D-terms of an anomalous U(1) gauge symmetry broken at the Planck scale. Effective action for these theories at sub-Planck energies (including higher dimensional terms in the superpotential) are severely restricted by the U(1) symmetry and by the assumption that they arise from an underlying renormalizable theory at a higher scale. Phenomenological consequences of these models are studied. They are found to have the attractive feature that the gaugino masses, the A and B terms and the mass splittings between the like-charged squarks of the first two generations compared to their average masses can all be naturally suppressed. As a result, the electric dipole moment of the neutron as well as the flavor changing neutral current effects are predicted to be naturally small. These models also predict the value of the $μ$-term to be naturally small and have the potential to qualitatively explain the observed mass hierarchy among quarks and leptons. We then discuss examples of high scale renormalizable theories that can justify the choice of the the effective action from naturalness point of view.

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arXiv1996

Astrophysical bounds on superlight gravitinos

We derive the allowed mass range for the superlight gravitino present in a large class of supersymmetric models from the observed luminosity from Supernova 1987A. We find that for photino masses of order 100 GeV, the mass range $2.6\times 10^{-6} eV \leq m_{\tilde{g}} \leq 2.2\times 10^{-8} eV$ for the gravitino $\tilde{g}$ is excluded by SN1987A observations. Unlike the bounds on $m_{\tilde{g}}$ from nucleosynthesis, the bounds in the present paper do not depend critically on the uncertainties of the observational input.

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arXiv1996

Anomalous $U(1)$ Mediated SUSY Breaking, Fermion Masses and Natural Suppression of FCNC and CP Violating Effects

We construct realistic supergravity models where supersymmetry breaking arises from the $D$-terms of an anomalous $U(1)$ gauge symmetry broken at the Planck scale. The model has the attractive feature that the gaugino masses, the $A$ and $B$ terms and the mass splittings between the like-charged squarks of the first two generations compared to their average masses are all suppressed. As a result, the electric dipole moment of the neutron as well as the flavor changing neutral current effects are predicted to be naturally small. These models predict naturally the expected value of the $μ$-term and also have the potential to qualitatively explain the observed mass hierarchy among quarks and leptons.

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arXiv1996

Higgs Boson Mass in Models with Gauge-Mediated Supersymmetry Breaking

We present the predictions for the mass $M_h$ of the lightest Higgs boson in models with gauge-mediated supersymmetry breaking as a function of the SUSY-breaking scale. We include all radiative corrections up to two loops and point out that if the CDF e+ e- two-photon event is interpreted in terms of these models, then the lightest Higgs boson should be lighter than 110 GeV.

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arXiv1996

Magnitude of R-parity violation in String Inspired GUTs

The nature of R-parity violating interactions in two classes of string inspired supersymmetric grand unified theories (SISUSY GUT), based on the gauge groups $SO(10)$ (and its subgroup $SU(2)_L\times SU(2)_R\times SU(4)_c\equiv G_{224}$) as well as $[SU(3)]^3$, are discussed and their strengths are related to the ratio of symmetry breaking scales present in the model. We first argue that for the R-parity violating couplings $λ_{R\!\!\!/}$ to be suppressed to the desired level, the $B-L$ local symmetry must break at an intermediate scale $M_{B-L}$ since $λ_{R\!\!\!/} =M_{B-L}/M_{GUT}$. We then construct scenarios where such intermediate scales arise being consistent with gauge coupling unification in a two-loop renormalization group study. In the resulting $SO(10)$ models, higher-dimensional-operator-induced R-parity violating couplings are potentially large (except in one case), and are therefore inconsistent with limits on the proton life time unless the couplings associated with the higher dimensional terms are fine tuned to very small values. However, the $[SU(3)]^3$ and $G_{224}$ models can be consistent if a certain class of quark-lepton coupling in the superpotential is forbidden by a discrete summetry (unrelated to R-parity). An interesting prediction of these models is neutron-anti-neutron oscillation with observable strength.

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arXiv1996

New Supernova Constraints on Sterile Neutrino Production

We consider the possibility that a light sterile-neutrino species $ν_S$ can be produced by $ν_e$ scattering during the cooling of a proto-neutron star. If we parameterize the sterile neutrino production cross-section by a parameter $A$ as $σ(ν_e X\rightarrow ν_S X) = A σ(ν_e X\rightarrow ν_e X)$, where $X$ is an electron, neutron or proton, we show that $A$ is constrained by limits to the conversion of $ν_e$ to $ν_S$ in the region between the sterile-neutrino trapping region and the electron-neutrino trapping region. This consideration excludes values of $A$ in the range between $10^{-4} \la A \la 10^{-1}$.

hep-ph↗

arXiv1996

Neutron-anti-neutron oscillation as a test of grand unification

We discuss the predictions for neutron-anti-neutron oscillation in various supersymmetric and non-supersymmetric grand unified theories. It is pointed out that in a new class of superstring inspired grand unified theories of $E_6$-type that satisfy gauge coupling unification, breakdown of B-L symmetry occurs at an intermediate scale leading in turn to $ΔB=1$ type R-parity violating interactions naturally suppressed to the level of $10^{-5}$ to $10^{-7}$. This inturn implies an $N-\bar{N}$ transition time of order $10^{10}$ to $10^{11}$ sec. which may be observable in the next generation of experiments. This model also satisfies the conditions needed for generating the cosmological baryon asymmetry of the right order of magnitude for a restricted range of the parameter space.

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arXiv1996

Structures in the Mirror Universe

The idea of the universe with a mirror sector having all particles and forces identical to those in the familiar sector has been proposed in the context of neutrino physics as well as superstring theories. Assuming that all the quark and charged lepton masses in the mirror universe are scaled by a common factor, $ζ$, as is required in one interpretation of the neutrino data, we investigate domains of the parameter $ζ$ where physical conditions are favorable for cooling in the age of the universe that can lead to the formation of compact structures given the initial condition $Ω_B =Ω_{\tilde{B}}$ ($\tilde{B}$ denoting the mirror baryon). In particular we ask whether there is a region in $ζ$-space for which primordial Jeans mass mirror clouds cannot cool in the present age of the universe. We find that for most of the area of interest in the parameter space, atomic hyperfine structure cooling is effective in a time period short compared to the age of the universe but long compared to the free fall time for globular-sized objects expected on the basis of simple Jeans length analysis.

astro-ph↗

arXiv1996

$SU(5)\times SU(5)$ Unification, Seesaw Mechanism and R-Conservation

A new supersymmetric grand unified model based on the gauge group $SU(5)\times SU(5)$ is discussed. The model has the feature that the conventional seesaw mechanism for neutrino masses is implemented using the $(15, 1)+(1,\bar{15)}$ representation. This multiplet may have a better chance of arising from level two compactification of superstring theories than the the ${bf \bar{126}}$ representation used in the SO(10) model. The model also naturally suppresses all R-parity violating interactions.

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arXiv1995

Asymmetric Inflationary Reheating and the Nature of Mirror Universe

The existence of a shadow world (or mirror universe) with matter and forces identical to that of the visible world but interacting with the latter only via gravity can be motivated by superstring theories as well as by recent attempts to understand the nature of a sterile neutrino needed if all known neutrino data are to be consistent with each other. A simple way to reconcile the constraints of big bang nucleosynthesis in such a theory is to postulate that the reheating temperature after inflation in the mirror universe is lower than that in the visible one. We have constructed explicit models that realize this proposal and have shown that the asymmetric reheating can be related to a difference of the electroweak symmetry breaking scales in the two sectors, which is needed for a solution of the neutrino puzzles in this picture. Cosmological implications of the mirror matter are also discussed.

hep-ph↗

arXiv1995

Upper bound on the $W_R$ mass in automatically R-conserving SUSY models

We show that in automatically R-conserving minimal SUSY left-right symmetric models there is a theoretical upper limit on the mass of the right-handed $W_R$ boson given by $M_{W_R}\leq g M_{SUSY}/f$, where $M_{SUSY}$ is the scale of supersymmetry breaking, g is the weak gauge coupling and $f$ is the Yukawa coupling responsible for generating the right-handed neutrino masses. If $M_{W_R}$ violates the above limit, the ground state of the theory breaks electromagnetism. The only way to avoid this bound while keeping the theory automatically R-conserving is to expand the theory to include very specific kinds of additional multiplets and demanding unnatural finetuning of their couplings.

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arXiv1995

New vector-scalar contributions to neutrinoless double beta decay and constraints on R-parity violation

We show that in minimal supersymmetric standard model (MSSM) with R-parity breaking as well as in the left-right symmetric model, there are new observable contributions to neutrinoless double beta decay arising from hitherto overlooked diagrams involving the exchange of one W boson and one scalar boson. In particular, in the case of MSSM, the present experimental bounds on neutrinoless double beta decay lifetime improves the limits on certain R-parity violating couplings by about two orders of magnitude. It is shown that similar diagrams also lead to enhanced rates for $μ^-\rightarrow e^+$ conversion in nuclei, which are in the range accessible to ongoing experiments.

hep-ph↗

arXiv1995

Reconciling Present Neutrino Puzzles: Sterile Neutrinos as Mirror Neutrinos

We suggest that recent neutrino puzzles that are the solar and atmospheric neutrino deficits as well as the possible neutrino oscillations reported by the LSND experiment and the possibility of massive neutrinos providing the hot component of the cosmological dark matter, can all be naturally explained by assuming existence of a mirror world described by an ``electroweak'' gauge symmetry $[SU(2)\times U(1)]'$, with the breaking scale larger by about factor of 30 than the scale of the standard $SU(2)\times U(1)$ model. An interesting aspect of this model is that the sterile neutrinos arise from the hidden mirror sector of the theory and thus their lightness is more natural than in the usual neutrino mass scenarios. The needed pattern of the neutrino mass matrix in this model is obtained by assuming a conserved ZKM-type global lepton number $\bar L=L_e+L_μ-L_τ$, which is violated by Planck scale effects. One implication of our proposal is that bulk of the dark matter in the universe is a warm dark matter consisting of few KeV mass particles rather than the 100 GeV range particles of the currently popular cold dark matter scenarios.

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arXiv1995

An Inverted Mass Hierarchy for Hot Dark Matter and the Solar Neutrino Problem.

The cosmological model in which 20% of the dark matter is shared by two nearly equal mass neutrinos fits the structure of the universe on all scales. This has been motivated a $ν_μ$-$ν_τ$ oscillation explanation of the deficit of atmospheric muon neutrinos. If the observed ratio of atmospheric $nu_μ$ to $ν_e$ has an alternative explanation, the cosmological model can be retained if the deficit of solar neutrinos is explained by $ν_e$-$ν_τ$ oscillation. In this case an inverted mass hierarchy is required with $m_{ν_μ}\ll m_{ν_e} \simeq m_{ν_τ}\approx 2.4$ eV. We show that if there exists an $L_e- L_τ$ symmetry in nature, both the near mass degeneracy of \nue\ and \nut\ as well as the consistency of the above values for neutrino masses with the negative results for neutrinoless double beta decay search experiments are easily understood. We show that this symmetry implemented in the context of a high-scale left-right symmetric theory with the see-saw mechanism can lead to a simple theoretical understanding of the desired form of the mass matrix.

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