arXiv subjects

Subhendra Mohanty

Publications and source records attributed to Subhendra Mohanty.

At least 73 records · Page 4Linked to original sources

arXiv2015

Lorentz Invariance Violation and IceCube Neutrino Events

The IceCube neutrino spectrum shows a flux which falls of as $E^{-2}$ for sub PeV energies but there are no neutrino events observed above $\sim 3$ PeV. In particular the Glashow resonance expected at 6.3 PeV is not seen. We examine a Planck scale Lorentz violation as a mechanism for explaining the cutoff of observed neutrino energies around a few PeV. By choosing the one free parameter the cutoff in neutrino energy can be chosen to be between 2 and 6.3 PeV. We assume that neutrinos (antineutrinos) have a dispersion relation $E^2=p^2 - (ξ_3/M_{Pl})~p^3$, and find that both $π^+$ and $π^-$ decays are suppressed at neutrino energies of order of few PeV. We find that the $μ^-$ decay being a two-neutrino process is enhanced, whereas $μ^+$ decay is suppressed. The $K^+\rightarrow π^0 e^+ ν_e$ is also suppressed with a cutoff neutrino energy of same order of magnitude, whereas $K^-\rightarrow π^0 e^- \bar ν_e$ is enhanced. The $n \rightarrow p^+ e^- \bar ν_e$ decay is suppressed (while the $\bar n \rightarrow p^- e^+ ν_e$ is enhanced). This means that the $\bar ν_e$ expected from $n$ decay arising from $p+γ\rightarrow Δ\rightarrow π^+ n$ reaction will not be seen. This can explain the lack of Glashow resonance events at IceCube. If no Glashow resonance events are seen in the future then the Lorentz violation can be a viable explanation for the IceCube observations at PeV energies.

hep-ph↗

arXiv2015

Higgs instability and de Sitter radiation

If the Standard Model (SM) of elementary particle physics is assumed to hold good to arbitrarily high energies, then, for the best fit values of the parameters, the scalar potential of the Standard Model Higgs field turns negative at a high scale $μ_{\rm inst}$. If the physics beyond the SM is such that it does not modify this feature of the Higgs potential and if the Hubble parameter during inflation ($H_{\rm inf}$) is such that $H_{\rm inf} \gg μ_{\rm inst}$, then, quantum fluctuations of the SM Higgs during inflation make it extremely unlikely that after inflation it will be found in the metastable vacuum at the weak scale. In this work, we assume that (i) during inflation, the SM Higgs is in Bunch-Davies vacuum state, and, (ii) the question about the stability of the effective potential must be answered in the frame of the freely falling observer (just like in Minkowski spacetime), and then use the well known fact that the freely falling observer finds Bunch-Davies vacuum to be in thermal state to show that the probability to end up in the electroweak vacuum after inflation is reasonably high.

hep-ph↗

arXiv2015

No scale SUGRA SO(10) derived Starobinsky Model of Inflation

We show that a supersymmetric renormalizable theory based on gauge group SO(10) and Higgs system {\bf {10 $\oplus$ 210 $\oplus$ 126 $\oplus$ $\overline{\bf 126}$}} with no scale supergravity can lead to a Starobinsky kind of potential for inflation. Successful inflation is possible in the cases where the potential during inflation corresponds to $SU(3)_C \times SU(2)_L \times SU(2)_R \times U(1)_{B-L}$, $SU(5)\times U(1)$ and flipped $SU(5)\times U(1)$ intermediate symmetry with a suitable choice of superpotential parameters. The reheating in such a scenario can occur via non perturbative decay of inflaton i.e. through "preheating". After the end of reheating, when universe cools down, the finite temperature potential can have a minimum which corresponds to MSSM.

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arXiv2015

Detecting Dipolar Dark Matter in Beam Dump Experiments

We study interaction of low mass dark matter within beam dump experiments. In particular we study the dipolar dark matter model which assumes that the dark matter couples to Standard Model particles via its electric or magnetic dipole moment. We analyse the constraints on this model in the context of a particular beam dump experiment E613 conducted in the Fermilab. We find that dark matter mass in the range of $1-10$ GeV with a magnetic dipole moment between $(0.33-1.5)\times 10^{-7}μ_B$ and a electric dipole moment between $(0.5-3)\times 10^{-17}$ e-cm. We compare the bounds from other experimental data, such as helioseismological data and direct detection experiments.

hep-ph↗

arXiv2015

Power law Starobinsky model of inflation from no-scale SUGRA

We consider a power law $\frac{1}{M^2}R^β$ correction to Einstein gravity as a model of inflation. The interesting feature of this form of generalization is that small deviations from the Starobinsky limit $β=2$ can change the value of tensor to scalar ratio from $r \sim \mathcal{O}(10^{-3})$ to $r\sim \mathcal{O}(0.1)$. We find that in order to get large tensor perturbation $r\approx 0.1$ as indicated by BKP measurements, we require the value of $β\approx 1.83$ thereby breaking global Weyl symmetry. We show that the general $R^β$ model can be obtained from a SUGRA construction by adding a power law $(Φ+\bar Φ)^n$ term to the minimal no-scale SUGRA Kähler potential. We further show that this two parameter power law generalization of the Starobinsky model is equivalent to generalized non-minimal curvature coupled models with quantum corrected $Φ^{4}$- potentials i.e. models of the form $ξΦ^{a} R^{b} + λΦ^{4(1+γ)}$ and thus the power law Starobinsky model is the most economical parametrization of such models.

hep-ph↗

arXiv2015

Red and blue tilted tensor spectrum from Gibbons-Hawking temperature

The scale invariant scalar and tensor perturbations, which are predicted from inflation, are eigenmodes in the conformal coordinates. The 'out' observer in the de Sitter space observes a thermal spectrum with a Gibbons-Hawking temperature $H/2π$ of these 'Bunch-Davies' particles. The tensor power spectrum observed in experiments can have an imprint of the Gibbons-Hawking thermal distribution due to the mode mixing between 'in' state conformal coordinates and the coordinate frame of the observer. We find that the the Bunch-Davies modes appear as thermal modes to the asymptotic Minkowski observer in the future and the power spectrum of the gravitational waves is blue-tilted with a spectral index $n_T \sim 1$ even in the standard slow-roll inflation. On the other hand if the coordinate frame of the observer is taken to be static coordinates, the tensor spectrum is red-tilted with $n_T\sim -1$. A likelihood analysis shows and find the best fit values of the slow-roll parameters for both cases. We find that the blue-tilted tensor gives a better fit and reconciles the PLANCK upper bound on the tensor-to-scalar ratio, $r <0.11$ with BICEP2 measurement of $r=0.2$. This supports the idea of particle production due to the mode mixing between the initial Bunch-Davies vacuum modes and the asymptotic Minkowski vacuum of the post-inflation universe.

hep-ph↗

arXiv2014

Muon anomalous magnetic moment and positron excess at AMS-02 in a gauged horizontal symmetric model

We studied an extension of the standard model with a fourth generation of fermions to explain the discrepancy in the muon $(g-2)$ and explain the positron excess seen in the AMS-02 experiment. We introduce a gauged $SU(2)_{HV}$ horizontal symmetry between the muon and the 4th generation lepton families. The 4th generation right-handed neutrino is identified as the dark matter with mass $\sim 700$ GeV. The dark matter annihilates only to $(μ^+ μ^-)$ and $(ν^c_μ~ν_μ)$ states via $SU(2)_{HV}$ gauge boson. The $SU(2)_{HV}$ gauge boson with mass $\sim 1.4$ TeV gives an adequate contribution to the $(g-2)$ of muon and fulfill the experimental constraint from BNL measurement. The higgs production constraints from 4th generation fermions is evaded by extending the higgs sector.

hep-ph↗

arXiv2014

Non-universal gaugino mass GUT models in the light of dark matter and LHC constraints

We perform a comprehensive study of $SU(5)$, $SO(10)$ and $E(6)$ supersymmetric GUT models where the gaugino masses are generated through the F-term breaking vacuum expectation values of the non-singlet scalar fields. In these models the gauginos are non-universal at the GUT scale unlike in the mSUGRA scenario. We discuss the properties of the LSP which is stable and a viable candidate for cold dark matter. We look for the GUT scale parameter space that leads to the the lightest SM like Higgs mass in the range of 122-127 GeV compatible with the observations at ATLAS and CMS, the relic density in the allowed range of WMAP-PLANCK and compatible with other constraints from colliders and direct detection experiments. We scan universal scalar ($m_0^G$), trilinear coupling $A_0$ and $SU(3)_C$ gaugino mass ($M_3^G$) as the independent free parameters for these models. Based on the gaugino mass ratios at the GUT scale, we classify 25 SUSY GUT models and find that of these only 13 models satisfy the dark matter and collider constraints. Out of these 13 models there is only one model where there is a sizeable SUSY contribution to muon $(g-2)$.

hep-ph↗

arXiv2014

Higgs Inflation in f(Φ,R) Theory

We generalize the scalar-curvature coupling model ${ξΦ^2 R}$ of Higgs inflation to $ {ξΦ^a R^b} $ to study inflation. We compute the amplitude and spectral index of curvature perturbations generated during inflation and fix the parameters of the model by comparing these with the Planck$+$WP data. We find that if the scalar self coupling $λ$ is in the range $(10^{-5}-0.1)$, parameter $a$ in the range $(2.3 -3.6)$ and $b$ in the range $(0.77-0.22)$ at the Planck scale, one can have a viable inflation model even for $ξ\simeq 1$. The tensor to scalar ratio $r$ in this model is small and our model with scalar-curvature couplings is not ruled out by observational limits on $r$ unlike the pure $\fracλ{4} Φ^4$ theory. By requiring the curvature coupling parameter to be of order unity, we have evaded the problem of unitarity violation in scalar-graviton scatterings which plague the $ξΦ^2 R$ Higgs inflation models. We conclude that the Higgs field may still be a good candidate for being the inflaton in the early universe if one considers higher dimensional curvature coupling.

astro-ph.CO↗

arXiv2013

Leptophilic dark matter in gauged $L_μ-L_τ$ extension of MSSM

Positron excess upto energies $\sim$350 GeV has been observed by AMS-02 result and it is consistent with the positron excess observed by PAMELA upto 100 GeV. There is no observed excess of anti-protons over the expected CR background. We propose a leptophilic dark matter with an $U(1)_{L_μ-L_τ}$ gauge extension of MSSM. The dark matter is an admixture of the $L_μ-L_τ$ gaugino and fermionic partners of the extra $SU(2)$ singlet Higgs boson, which break the $L_μ-L_τ$ symmetry. We construct the SM$\otimes U(1)_{ L_μ-L_τ}$ SUSY model which provides the correct relic density of dark matter and is consistent with constrain on $Z'$ from LHC. The large dark matter annihilation cross-section into $μ^{+}μ^{-}$ and $τ^{+}τ^{-}$, needed to explain PAMELA and AMS-02 is achieved by Breit-Wigner resonance.

hep-ph↗

arXiv2013

Reconciling the Muon g-2 and Dark Matter Relic Density with the LHC Results in Nonuniversal Gaugino Mass Models

Relatively light electroweak superparticle masses are required to satisfy the bulk annihilation region of dark matter relic density and account for the observed excess of muon g-2, while TeV scale squark and gluino masses are required to account for the 125 GeV Higgs boson mass and the negative SUSY search results from LHC. These two sets of requirements can be reconciled in a simple nonuniversal gaugino mass model, which assumes SUSY breaking via a combination of two superfields belonging to the singlet and the 200-plet representations of the GUT group SU(5). The model can be probed via squark/gluon search with the present and future LHC data. In a more general nonuniversal gaugino mass model the squark and gluino masses can be raised to the edge of the discovery limit of LHC or beyond. This model can be probed, however, through the search for electroweak pair production of the relatively light sleptons and winos with the future LHC data.

hep-ph↗

arXiv2013

Pseudo-Dirac neutrinos via mirror-world and depletion of UHE neutrinos

We propose a possible particle physics explanation of the non-observation of muon neutrino events at IceCube coincident with GRB gamma ray at the rates predicted by the standard Bahcall-Waxman model, in terms of neutrino oscillations. Our model is based on assuming that (a) all neutrinos are pseudo-Dirac particles and (b) there exists a mirror world interacting gravitationally with the observed world. This scenario has three sterile neutrinos associated with each flavour of ordinary neutrinos. Very tiny mass splitting between these neutrinos is assumed to arise from lepton number violating dimension five operators suppressed by the Planck scale. We show that if a mass splitting of 10^(-15) eV^2 is induced between the four mass eigenstates of a given species, then its flux will be suppressed at IceCube energies by a factor of 4 which could be the explanation of the IceCube observation that the muon neutrino flux is lower than expected. Hierarchies in mass splitting among different flavours may result in different amount of suppression of each flavour and based on this, we predict a difference in the flavour ratios of the observed neutrinos which is significantly different compared to the standard prediction of nu_e:nu_mu:nu_tau=1:1:1 which could serve as a test for this model.

hep-ph↗

arXiv2013

130 GeV gamma ray line and enhanced Higgs di-photon rate from Triplet-Singlet extended MSSM

We propose an economic extension of minimal supersymmetric standard model with a SU(2) singlet and Y=0 triplet, which can explain (i) the 125 GeV Higgs boson without fine tuning, (ii) the 130 GeV $γ$-ray line seen at Fermi-LAT, (as well as a second photon line at 114 GeV)(iii) an enhanced Higgs di-photon decay rate seen by ATLAS, while being consistent with dark matter relic density and recent XENON 100 exclusion limits on spin-independent direct detection cross-section. We obtain the required cross-section of $10^{-27}cm^3s^{-1}$ for the 130 GeV $γ$-ray flux through the resonant annihilation of dark matter via pseudoscalar triplet Higgs of mass $\sim$260 GeV. The dark matter is predominantly bino-higgsino which has large couplings with photons (through higgsino) and gives correct relic density (through bino). We get the enhanced Higgs diphoton decay rate, $R_{γγ}\simeq 1.24$ dominantly contributed by the light chargino-loops, which can account for the reported excess seen in the $h\rightarrow γγ$ channel by ATLAS.

hep-ph↗

arXiv2013

130 GeV Gamma Ray Signal in NMSSM by Internal Bremsstrahlung

There is a possible γ-ray signal at 130 GeV coming from the Galactic Center as seen by Fermi-LAT experiment. We give a SUSY dark matter model to explain this γ-ray feature in NMSSM. We show that in NMSSM, one can have a benchmark set in which the γ-ray signal arises from final state γ's in the $χχ\to f \bar f γ$ annihilation of a 130 GeV bino dark matter requiring a boost factor of ~590 to fit the γ-ray signal. In addition, this benchmark set also gives the correct relic density, lightest Higgs mass of 125 GeV and is consistent with constraints on SUSY from LHC. This dark matter model evades the XENON100 constraint but is testable in a future XENON1T experiment.

hep-ph↗

arXiv2013

Relic density and PAMELA events in a heavy wino dark matter model with Sommerfeld effect

In a wino LSP scenario the annihilation cross section of winos gravitationally bound in galaxies can be boosted by a Sommerfeld enhancement factor which arises due to the ladder of exchanged W bosons between the initial states. The boost factor obtained can be in the range S ~ 10^4 if the mass is close to the resonance value of M ~ 4 TeV. In this paper we show that if one takes into account the Sommerfeld enhancement in the relic abundance calculation then the correct relic density is obtained for 4 TeV wino mass due to the enhanced annihilation after their kinetic decoupling. At the same time the Sommerfeld enhancement in the χχ--> W^+ W^- annihilation channel is sufficient to explain the positron flux seen in PAMELA data without significantly exceeding the observed antiproton signal. We also show that (e^- + e^+) and gamma ray signals are broadly compatible with the Fermi-LAT observations. In conclusion we show that a 4 TeV wino DM can explain the positron and antiproton fluxes observed by PAMELA and at the same time give a thermal relic abundance of CDM consistent with WMAP observations.

hep-ph↗

arXiv2013

Explanation for the low flux of high energy astrophysical muon-neutrinos

We consider the possibility that some exotic neutrino property is responsible for reducing the muon neutrino flux at high energies from distant neutrino sources; specifically, we consider (i) neutrino decay and (ii) neutrinos being pseudo-Dirac particles. This would provide a mechanism for the lack of high energy muons in the Icecube detector.

hep-ph↗

arXiv2012

Predictions of a Natural SUSY Dark Matter Model for Direct and Indirect Detection Experiments

The most natural region of cosmologically compatible dark matter relic density in terms of low fine-tuning in a minimal supersymmetric standard model with nonuniversal gaugino masses is the so called bulk annihilation region. We study this region in a simple and predictive SUSY-GUT model of nonuniversal gaugino masses, where the latter transform as a combination of singlet plus a nonsinglet representation of the GUT group SU(5). The model prediction for the direct dark matter detection rates is well below the present CDMS and XENON100 limits, but within the reach of a future 1Ton XENON experiment. The most interesting and robust model prediction is an indirect detection signal of hard positron events, which resembles closely the shape of the observed positron spectrum from the PAMELA experiment.

hep-ph↗

arXiv2012

Triplet-Singlet Extension of the MSSM with a 125 Gev Higgs and Dark Matter

We study the extension of Minimal Supersymmetric Standard Model by adding one singlet and one hypercharge zero SU(2) triplet chiral superfield. The triplet sector gives an additional contributions to the scalar masses and we find that the lightest CP-even Higgs boson can have a mass of 119-120 GeV at the tree level, and radiative correction raises the value to 125 GeV. In this model no significant contributions from stop loops is needed to get the required Higgs mass which alleviates the fine tuning problem of fixing the stop mass to a high precision at the GUT scale. In addition this model gives a neutralino dark matter of mass around 100 GeV which is a mixture of Higgsino and Triplino with a dark matter density consistent with WMAP observations. The spin-independent scattering cross-section with nucleons is 10^(-43) cm^2, which makes it consistent with the bounds from direct detection experiments like XENON100 and others.

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