Search

The strength of the HI signal originating from a distant galaxy at a cosmological distance is several orders of magnitude lower than the foreground and background noise and hence it is difficult to observe this signal at a given radio telescope. However, a few recent studies reported the detection of that signal at the radio band suggests the strength of this signal is somehow magnified. In this analysis, we study the prospects of detecting this signal at different frequency bands of the uGMRT where this signal is supposed to be amplified through the strong gravitational lensing by an isolated neutron star located in a cosmological distance. Our study shows the effects of the lensing parameters on the observables of that amplified signal and discusses its variation with the frequency bands considered here. We present a method to estimate the position and size of an isolated neutron star using the signal-to-noise ratio of that signal supposed to be detected at different frequency bands of the uGMRT. We discuss the scope of multi-messenger astronomy in the era of HI observation where the estimated lensing parameters can be cross-validated using the pulsar detection at the X-ray band from the same location in the sky. Our analysis is equally applicable to any radio telescope with given specifications., Comment: 16 Pages, 4 figures, comments and suggestions are welcome

We investigate an interacting quintessence dark energy - dark matter scenario and its impact on structure formation by analyzing the evolution of scalar perturbations. The interaction is introduced by incorporating a non-zero source term into the continuity equations of the two sectors (with opposite signs), modeled as $\bar{Q}_0 \equiv \alpha\bar{\rho}_{\rm m}(H + \kappa\dot{\phi})$. The coupling parameter $\alpha$ and the parameter $\lambda$ involved in quintessence potential $V(\phi) = V_0e^{-\lambda\kappa\phi}$, play crucial roles in governing the dynamics of evolution examined within the present framework. The cosmic evolution, within this context, is depicted as a first-order autonomous system of equations involving appropriately chosen dynamical variables. We analyzed the associated stability characteristics and growth rate of perturbations and obtained domains in the ($\alpha-\lambda$) parameter space for which fixed points can exhibit stable and non-phantom accelerating solutions. Depending on its magnitude, the coupling parameter $\alpha$ has the potential to change the characteristics of certain critical points, altering them from attractors to repellers. This model effectively captures the evolutionary features of the universe across its various phases at both the background and perturbation levels. The issue of cosmic coincidence can also be addressed within the framework of this model. We also observed that for a moderate strength of coupling, the growth rate of matter perturbation extends into the distant future., Comment: 23 pages, 2 tables and 6 figures

Determination of neutrino mass ordering and precision measurement of neutrino oscillation parameters are the foremost goals of the JUNO experiment. Here, we explore the effects of scalar non-standard interactions (sNSI) on the electron neutrino survival probability measured by JUNO. sNSI appears as a correction to the neutrino mass term in the Hamiltonian. We have considered the simplest scenario where there is only one NSI ($\eta_{ee}$) present in the theory. Our results show that sNSI can have significant effect on neutrino oscillation probabilities at the medium- and long-baseline reactor experiments. We fit KamLAND data assuming non-zero sNSI in theory and find that {\it estimates of $\Delta m^2_{21}$ and $\theta_{12}$ from KamLAND deviate significantly from their standard best-fit values} if one assumes sNSI in the theory. $\eta_{ee} \in [-1.0, 1.0]$ is allowed by KamLAND. JUNO cannot constrain sNSI but it can robustly measure $\Delta m^2_{21}$ and $\theta_{12}$ even when they differ widely from their current best-fit values. {\it Our works highlight the necessity of global analysis of constraints on sNSI and standard two-flavour oscillation parameters before arduous three-flavour questions such as neutrino mass ordering or CP violation in their presence is attempted., Comment: 25 pages, 6 figures. In the previous version, density subtraction was not done and robustness of standard oscillation parameters was assumed. In this version, we first constrain the solar oscillation parameters using KamLAND data and then reassess the potential of JUNO towards neutrino oscillation measurements in the presence of scalar NSI. Our results and conclusion have changed

The self-interacting dark matter can affect various cosmological processes. Such interactions can be number conserving (\emph{e.g.} $2 \rightarrow 2$) or number violating (\emph{e.g.} $3 \rightarrow 2,\,4 \rightarrow 2$ etc.). The latter processes where three (or more) dark matter particles undergo self-annihilation/scattering to produce less number of dark matter is termed as ``Cannibalism'' process. In this work, the self-interaction of dark matter and the strength of such interactions are investigated in the light of experimental results of the global 21-cm spectrum of neural hydrogen from the era of cosmic dawn. From the present work, it appears that $2\rightarrow 2$ process is much more dominant over the $3\rightarrow 2$ process. It is also found that such interactions affect the dark matter-baryon elastic scattering cross-section. The study also indicates the presence of multi component dark matter of different mass range in the Universe., Comment: 19 pages, 5 figures

The Weakly Interacting Massive Particles (WIMPs) so far remain one of the most popular candidates for dark matter. If captured gravitationally inside the core of the Sun, these WIMPs may produce high energy neutrinos as the end product in case they undergo self annihilations at the solar core. In this work, we address the detectability of such neutrinos at the proposed KM3NeT detector. Upper bounds of the detection rate for such neutrinos at KM3NeT are computed for the case of a generic dark matter scenario and also when specific models for particle dark matter are chosen. In this work, upper bounds of muon event rates for different annihilating dark matter masses are computed for each of the cases of dark matter annihilation channels (e.g. $b\bar{b}~, W^+W^-, Z\bar{Z} $ etc). These upper bounds are also computed by considering the dark matter scattering cross-section using upper bounds obtained from PandaX-4T direct dark matter search experiment., Comment: New appendix and results are added; matches the published version

The evaporation of Primordial Black Hole (PBH) via Hawking radiation influences the evolution of Inter Galactic Medium by heating up the latter and consequently affects the 21cm signal originated from the neutral Hydrogen atoms. In this work, we have considered EDGES observational data of 21cm line corresponding to cosmic dawn era to constrain the mass and the abundance of PBHs. In this context, two different PBH mass distributions namely, power law and lognormal mass distributions are considered to estimate the effects of PBH evaporation on the 21cm brightness temperature $T_{21}$. In addition to these two mass distributions, different monochromatic masses are also considered. The impacts of Dark Matter - baryon interactions on $T_{21}$ are also considered in this work along with the influences of PBH evaporation. Furthermore, adopting different monochromatic masses for PBHs, an attempt has been made to formulate a distribution for PBH masses by associating a probability weightage of the $T_{21}$ values (at $z \sim 17.2$), within the range given by EDGES experiment, with the calculated $T_{21}$ values for each of the PBH mass values. The distribution best suited for the present purpose is found to be a combination of an error function and Owen function. Allowed contours in the parameter space of (initial PBH mass-dark matter mass) are obtained., Comment: 17 pages, 9 figures

The evaporations of Primordial Black Holes (PBH) (via Hawking radiation) can produce electrons/positrons ($e^-/e^+$) in the Galactic Centre (GC) region which under the influence of the magnetic field of Centre region can emit synchrotron radiation. These $e^-/e^+$ can also induce Inverse Compton radiation due to the scattering with ambient photons. In this work three different PBH mass distributions namely, monochromatic, power law and lognormal distributions are considered to calculate such radiation fluxes. On the other hand, annihilation or decay of dark matter in the Galactic Centre region can also yield $e^-/e^+$ as the end product which again may emit synchrotron radiation in the Galactic magnetic field and also induce Inverse Compton scattering. In this work a comparative study is made for these radiation fluxes from both PBH evaporations and from dark matter origins and their detectabilities are addressed in various ongoing and other telescopes as well as in upcoming telescopes such as SKA. Moreover, constraints on the model parameters are obtained from these experimental predictions. The variations of these radiation fluxes with the distance from the Galactic Centre are also computed and it is found that such variations could be a useful probe to determine the mass of PBH or the mass of dark matter., Comment: 33 pages, 17 figures

The primordial heavy or superheavy dark matter that could be created during the reheating or preheating stage of the Universe can undergo QCD cascade decay process to produce leptons or $\gamma$ as end products. Although these could be rare decays, the energy involved in such decay process can influence 21-cm signal of hyperfine transition of neutral hydrogen during the reionization era. We explore in this work, possible multimessenger signals of such heavy dark matter decays. One of which could be the source of ultra high energy neutrino (of $\sim$ PeV energy regime) signals at IceCube detector whereas the other signal attributes to the cooling/heating of the baryons by the exchange of energy involved in this decay process and its consequent influence on 21-cm signal. The effect of evaporation of primordial black holes and baryon scattering with light cold dark matter are also included in relation to the evolution of the 21-cm signal temperature and their influence are also discussed., Comment: 23 pages, 4 figures

We study the fluctuations in the brightness temperature of 21-cm signal $\delta T_{21}$ at the dark ages ($z\sim100$) with a dark matter candidate in Inter Doublet Model (IDM). We then explore the effects of different fractions of IDM dark matter on $\delta T_{21}$ signal. The IDM dark matter masses are chosen in few tens of GeV region as well as in the high mass region beyond 500 GeV. It has been observed that the $\delta T_{21}$ signal is more sensitive in the dark matter mass range of $70 - 80$ GeV. A lower bound on annihilation cross-section for this dark matter is also obtained analyzing the $\delta T_{21}$ signal. This is found to lie within the range $6.5 \times 10^{-29} \,\, \rm{cm^3 / sec} \leq \langle\sigma v\rangle \leq 4.88\times 10^{-26}\,\, \rm{cm^ 3 / sec}$ for the IDM dark matter mass range $10 \, {\rm GeV} \leq m_{\chi}\leq 990 \,{\rm GeV} $., Comment: 13 pages, 9 figures, 1 table, comments and suggestions are welcome

We consider a simple extension of Standard Model by adding two complex singlet scalars with a $\rm{U}\left(1\right)$ symmetry. A discrete $\mathcal{Z}_2 \times \mathcal{Z}^{\prime}_2$ symmetry is imposed in the model and the added scalars acquire a non zero vacuum expectation value (VEV) when the imposed symmetry is broken spontaneously. The real (CP even) parts of the complex scalars mix with the SM Higgs and give three physical mass eigenstates. One of these physical mass eigenstates is attributed to the SM like Higgs boson with mass 125.09 GeV. In the present scenario, domain walls are formed in the early Universe due to the breaking of discrete $\mathcal{Z}_2 \times \mathcal{Z}^{\prime}_2$ symmetry. In order to ensure the unstability of the domain wall this discrete symmetry is also explicitly broken by adding a bias potential to the Lagrangian. The unstable annihilating domain walls produce a significant amount of gravitational waves (GWs). In addition, we also explore the possibility of the production of GW emission from the strong first-order phase transition. We calculate the intensities and frequencies of each of such gravitational waves originating from two different phenomena of the early Universe namely annihilating domain walls and strong first-order phase transition. Finally, we investigate the observational signatures from these GWs at the future GW detectors such as ALIA, BBO, DECIGO, LISA, TianQin, Taiji, aLIGO, aLIGO+ and pulsar timing arrays such as SKA, IPTA, EPTA, PPTA, NANOGrav11 and NANOGrav12.5., Comment: 30 pages, 3 figures and 5 tables

The EDGES experiment has observed an excess trough ($-500^{+200}_{-500}$ mK) in the brightness temperature $T_{21}$ of the 21cm absorption line of neutral Hydrogen atom (HI) from the era of cosmic dawn ($z \simeq 17.2$). We consider possible interaction of Dark Matter and Dark Energy fluid along with the cooling off of the baryon matter by its collision with Dark Matter to explain the observed excess trough of $T_{21}$. We make use of three different Dark Matter-Dark Energy (DM-DE) interaction models to taste the viability of those models in explaining the EDGES results. The evolution of Hubble parameter is modified by DM-DE interactions and this is also addressed in this work. This in turn influences the optical depth of HI 21cm as well as the baryon temperature and thus effects the $T_{21}$ brightness temperature. In addition we also find that the DM-DE interaction enables us to explore Dark Matter with varied mass regimes and their viabilities in terms of satisfying the EDGES result., Comment: 19 pages, 10 figures

We revisit dark matter annihilation as an explanation of the positron excess reported recently by the AMS-02 satellite-borne experiment. To this end, we propose a particle dark matter model by considering a Two Higgs Doublet Model (2HDM) extended with an additional singlet boson and a singlet fermion. The additional (light) boson mixes with the pseudoscalar inherent in the 2HDM, and the singlet fermion, which is the dark matter candidate, annihilates via this bosonic portal. The dark matter candidate is made leptophilic by choosing the lepton-specific 2HDM and a suitable high value of $\tan\beta$. We identify the model parameter space which explains the muon g-2 anomaly while evading the experimental constraints. After establishing the viability of the singlet fermion to be a dark matter candidate, we calculate the positron excess produced from its annihilation to the light bosons which primarily decay to muons. Incorporating the Sommerfeld effect caused by the light mediator and an appropriate boost factor, we find that our proposed model can satisfactorily explain the positron fraction excess as well as the positron spectrum data reported by AMS-02 experiment., Comment: 19 pages, 6 figures, 2 tables, Title modified, Text changed, Figures modified

Violation of equivalence principle predicts that neutrinos of different flavor couple differently with gravity. Such a scenario can give rise to gravity induced flavor oscillations in addition to the usual mass flavor neutrino oscillations during the neutrino propagation. Even if the equivalence principle is indeed violated, their measure will be extremely small. We explore the possibility to probe the violation of equivalence principle (VEP) for the case of long baseline (LBL) neutrinos in a 4-flavor neutrino framework (3 active + 1 sterile) where both mass and gravity induced oscillations are considered. To this end, we have explicitly calculated the oscillation probability in 4-flavor framework that includes in addition to the mass-flavor mixing in matter, the gravity-flavor mixing also. The energy eigenvalues are then obtained by diagonalizing such a 4-flavor mixing matrix. The formalism is then employed to estimate the wrong and right sign muon yields at a far detector for neutrinos produced in a neutrino factory and travel through the Earth matter. These results are compared with the similar estimations when the usual three active neutrinos are considered., Comment: 27 pages LaTeX, 6 figures

The recent results of IceCube Neutrino Observatory include an excess of PeV neutrino events which appear to follow a broken power law different from the other lower energy neutrinos detected by IceCube. The possible astrophysical source of these neutrinos is still unknown. One possible source of such neutrinos could be the decay of non-thermal, long-living heavy mass Dark Matter, whose mass should be $> 10^{6} \rm {GeV}$ and could have produced at the very early Universe. They can undergo cascading decay via both hadronic and leptonic channels to finally produce such high energy neutrinos. This possibility has been explored in this work by studying the decay flux of these Dark Matter candidates. The mass and lifetime of such Dark Matter particles have been obtained by performing a $\chi^2$ fit with the PeV neutrino data of IceCube. We finally estimate the baryon asymmetry produced in the Universe due to such Dark Matter decay., Comment: 25 pages, 7 figures

The mass to luminosity ratio of the dwarf satellite galaxies in the Milky Way suggests that these dwarf galaxies may contain substantial dark matter. The dark matter at the dense region such as within or at the vicinity of the centres of these dwarf galaxies may undergo the process of self annihilation and produce $\gamma$-rays as the end product. The satellite borne $\gamma$-ray telescope such as Fermi-LAT reported the detection of $\gamma$-rays from around 45 Dwarf Spheroidals (dSphs) of Milky Way. In this work, we consider particle dark matter models described in the literature and after studying their phenomenologies, we calculate the $\gamma$-ray fluxes from the self annihilation of the dark matter within the framework of these models in case of each of these 45 dSphs. we then compare the computed results with the observational upper bounds for $\gamma$-ray flux reported by Fermi-LAT and Dark Energy Survey (DES) for each of the 45 dSphs. The fluxes are calculated by adopting different dark matter density profiles. We then extend similar analysis for the observational upper bounds given by Fermi-LAT for the continuum $\gamma$-ray fluxes originating from extragalactic sources.

Considering the ultrahigh energy (UHE) neutrino events reported by IceCube in the PeV regime to have originated from the decay of superheavy dark matter, the IceCube UHE neutrino events are analysed and the best fit values of the two parameters namely the mass of the superheavy dark matter and its decay lifetime are obtained. The theoretical astrophysical flux is also included in theanalysis. We find that while the neutrino events in the energy range $\sim$ 60 TeV-$\sim$ 120 TeV appears to have astrophysical origin, the events in the energy range $\sim 1.2 \times 10^5$ GeV - $\sim 5 \times 10^7$ GeV can be well described from the superheavy dark matter decay hypothesis. We also find that although hadronic decay channel of the superheavy dark matter can well explain the events in the energy range $\sim 1.2 \times 10^5$ GeV - $\sim 5 \times 10^6$ GeV, the higher energy regime higher than this range can be addressed only when the leptonic decay channel is considered., Comment: 23 pages LaTeX, 12 eps figures

We consider a dark energy scenario driven by a scalar field $\phi$ with a pseudo Nambu Goldstone boson (pNGB) type potential $V(\phi)=\mu^4 \left( 1+ {\rm cos}(\phi/f) \right)$. The pNGB originates out of breaking of spontaneous symmetry at a scale $f$ close to Planck mass $M_{\rm{pl}}$. We consider two cases namely the quintessence dark energy and the other, where the standard pNGB action is modified by the terms related to Slotheon cosmology. We demonstrate that for this pNGB potential, high-$f$ problem is better addressed when interaction between dark matter and dark energy is taken into account and that Slotheon dark energy scenario works even better over quintessence in this respect. To this end, a mass limit for dark matter is also estimated., Comment: 20 pages, 12 figures

Recent detection of the neutrino events IceCube-170922A, 13 muon-neutrino events observed in 2014-2015 and IceCube-141209A by IceCube observatory from the Blazars, namely TXS 0506+056, PKS 0502+049/TXS 0506+056 and GB6 J1040+0617 respectively in the state of enhanced gamma-ray emission, indicates the acceleration of cosmic rays in the blazar jets. The photo-meson ($p\gamma$) interaction cannot explain the IceCube observations of 13 neutrino events. The non-detection of broadline emission in the optical spectra of the IceCube blazars, however, question the hadronuclear (pp) interaction interpretation through relativistic jet meets with high density cloud. In this work, we investigate the proton blazar model in which the non-relativistic protons that come into existence under the charge neutrality condition of the blazar jet can offer sufficient target matter for $pp$ interaction with shock-accelerated protons, to describe the observed high-energy gamma-rays and neutrino signal from the said blazars. Our findings suggest that the model can explain consistently the observed electromagnetic spectrum in combination with appropriate number of neutrino events from the corresponding blazars., Comment: 12 pages, four figures. arXiv admin note: text overlap with arXiv:1908.11849

We consider a particle dark matter model by extending the scalar sector of the Standard Model by an additional SU(2) scalar doublet which is made "inert" (and stable) by imposing a discrete $Z_2$ symmetry under which the additional scalar doublet is odd (and the SM is even) and it does not develop any vacuum expectation value (VEV). The lightest inert particle (LIP) of this inert doublet model (IDM) can be a viable candidate for Dark Matter. The IDM model is further extended by an additional singlet scalar which is also even under $Z_2$ and develop a VEV on spontaneous symmetry breaking. This additional scalar singlet mixes with SM Higgs and on diagonalisation of the mass matrix two CP even scalar eigenstates are obtained one of which is attributed to the physical Higgs (with mass 125.09 GeV). The LIP is the dark matter candidate in the extended model. For such a particle dark matter model we explore the first-order electroweak phase transition and the consequent production of Gravitational Waves (GW) at that epoch of the early Universe and calculate the intensities and frequencies for such waves. We then investigate the detection possibilities of such GWs at the future spaceborne primordial GW detectors such as eLISA, BBO, ALIA, DECIGO, U-DECIGO and ground-based detector aLIGO., Comment: 28 pages, 6 figures and 2 tables

Considering that the ultrahigh energy (UHE) upgoing muon neutrino events around the PeV energy region observed by the IceCube are due to the decay of super heavy dark matter to neutrinos, we constrain the mass of the decaying dark matter and its decay lifetime using the IceCube analysis of these neutrinos in the PeV region. The theoretical fluxes are computed by adpoting the procedure given in the reference [1,2], where the DGLAP numerical evolutions of QCD cascades as well as electroweak corrections are included for evolving the decay process of the super heavy dark matter. Our results indicate that to explain the IceCube events around PeV region the decaying dark matter mass $m_\chi$ would be $ \sim 5 \times 10^{7}$ GeV with the decay lifetime $\tau \sim 7 \times 10^{28}$ sec., Comment: 12 pages LaTeX, 5 eps figures

We explore in this work whether Slotheon model of Dark Energy obeys the Swampland criteria of string theory. Since de Sitter vacuum is very difficult to construct in string theory the cosmological constant as an explanation of Dark Energy is almost ruled out in string theory since it involves a scalar potential $V$ with positive local minimum that ends up to a stable (or meta stable) de Sitter (ds) vacuum. In quintessence model however if the derivative of the scalar potential $V$ ($\nabla V$) is small and $\frac{|\nabla V|}{V} \sim {\cal {O}}(1)$ then in this situation the potential $V$ can be positive but the scalar field may not be at the minimum. For a consistent quantum theory of gravity the theory should not have any ds or meta stable ds vacua. In this regard the Swampland criterion is proposed which any low energy theory should obey to be consistent with quantum theory of gravity. This criterion is written as $|\nabla V|/V > c \sim {\cal {O}}(1)$. In this work we consider a scalar field model for Dark Energy namely the Slotheon Dark Energy model inspired by the theories of extra dimensions and show that this Dark Energy model agrees better with the Swampland criteria than the quintessence Dark Energy model., Comment: 15 pages LaTeX, 5 figures

Within the framework of modified gravity model namely Slotheon model, inspired by the theory of extra dimensions, we explore the behaviour of Dark Energy and the perturbations thereof. The Dark Energy and matter perturbations equations are then derived and solved numerically by defining certain dimensionless variables and properly chosen initial conditions. The results are compared with those for standard quintessence model and $\Lambda$CDM model. The matter power spectrum is obtained and also compared with that for $\Lambda$CDM model. It appears that Dark Energy in Slotheon model is more akin to that for $\Lambda$CDM model than the standard quintessence model., Comment: 20 pages LaTeX, 6 figures

The gravitational waves (GWs) has been a topic of interest for its versatile capabilities of probing several aspects of cosmology and early Universe. Gravitational lensing enhances further the extent of this sort of waves and upgrade our understanding to a next level. Besides several similarities with optical waves, GWs are capable of passing through optically opaque celestial objects like stars, exoplanets unlike light waves and manifest a different kind of lensing effect. In this work we have explored the lensing action of compact objects on gravitational waves using numerical means. After modeling the internal mass distribution of the compact objects by TOV equations and tracing wavefronts using geodesic equations, we have found that the GWs are indeed lensed in a manner analogous to the optical lensing of light in presence of a thick optical lens by producing spherical aberration in the focused waves. The distance to the best focused point shows significant dependence with the mass and radius of the lensing star and unlike gravitational lensing, the region inside and outside compact objects responds differently to the incoming waves., Comment: Total 10 pages, 6 figures

We propose a fermionic dark matter model by extending Standard Model with a Dirac fermion and a real pseudoscalar. The fermion dark matter particle interacts with the Standard Model sector via the Higgs portal through a dimension five interaction term as also through a pseudoscalar interaction term. The parameter space of the model is then constrained by using the vacuum stability and perturbativity condition as also with the LHC constraints. They are finally constrained by the PLANCK results for dark matter relic densities. The direct detection limits are then ensured to have satisfied by the model. We then explore within the framework of the model, the possible signatures of synchrotron radiation from the annihilations of dark matter in the Galactic Centre region when the end product is $e^+e^-$. We consider the observational data from the radio telescopes namely SKA, GMRT and Jodrell Bank telescopes and compare our calculated synchrotron flux density with them and also with the results predicted by these experiments. We predict that if the low frequency radio telescopes like GMRT, SKA operate at the peak frequencies obtained from our calculations should get a better r.m.s sensitivity., Comment: 35 pages, 8 figures

Gravitational waves from binary black hole pairs have emerged as an important observational tool in current times. The energy of the BH - BH binary pair is radiated in the form of gravitational waves and to compensate for that energy, kinetic energy of the system decreases gradually. Consequently the mutual separation of the objects decreases with time and tends to merge. The whole process may require a very long time comparable or longer than the age of the universe, specially in the case of low mass mergers. We have examined the case in which a massive object compared to the individual masses comprising the binary pair is present nearby such a system. We have found that in this case the merging process takes place much rapidly than that of the conventional BH-BH merging process. Scenarios with both an Intermediate Mass Black Hole (IBMH) ($10^{5}\:M_{\odot}$) as well as a Super Massive Black Hole (SMBH) have been studied and the latter has been found to provide a much higher overall rate for the BH-BH merger process., Comment: 17 Pages, 12 figures

Neutron stars generally cools off by the emission of gamma rays and neutrinos. But axions can also be produced inside a neutron star by the process of nucleon-nucleon axion bremsstrahlung. The escape of these axions adds to the cooling process of neutron star. We explore the nature of cooling of neutron stars including the axion emission and compare our result with the scenario when the neutron star is cooled by only the emission of gamma rays and neutrinos. In our calculations we consider both the degenerate and non-degenerate limits for such axion energy loss rate and the resulting variation of luminosity with time and variation of surface temperature with time of the neutron star. In short the thermal evolution of a neutron star is studied with three neutron star masses (1.0, 1.4, 1.8 solar masses) and by including the effect of axion emission for different axion masses ($m_{a}=10^{-5}\rm{eV}, 10^{-3}\rm{eV}, 10^{-2}\rm{eV}$) and compared with the same when the axion emission is not considered. We compared theoretical cooling curve with the observational data of three pulsars PSR B056+14, Geminga and PSR B1055-52 and finally give an upper bound on axion mass limits $m_{a}\leq10^{-3}$ eV which implies that the axion decay constant $f_{a}\geq0.6\times10^{10}\hspace{1mm}\rm{GeV}$., Comment: 17 pages, 10 Figures, minor changes

We consider a four flavour scenario for the neutrinos where an extra sterile neutrino is introduced with the three families of active neutrinos and study the deviation from three flavour scenario in the ultra high energy (UHE) regime. We calculate the possible muon and shower yields at a 1 Km$^2$ detector such as ICECUBE for these neutrinos from distant UHE sources namely Gamma Ray Bursts (GRBs) etc. Similar estimations for muon and shower yields are also obtained for three flavour case. Comparing the two results we find considerable differences of the yields for these two cases. This can be useful for probing the existence of a fourth sterile component using UHE neutrino flux., Comment: 23 pages LaTeX, 5 eps figures, minor changes and corrected typos

We explore the idea of an alternative candidate for particle dark matter namely Feebly Interacting Massive Particle (FIMP) in the framework of a two component singlet scalar model. Singlet scalar dark matter has already been demonstrated to be a viable candidate for WIMP (Weakly Interacting Massive Particle) dark matter in literature. In the FIMP scenario, dark matter particles are slowly produced via "thermal frreze-in" mechanism in the early Universe and are never abundant enough to reach thermal equilibrium or to undergo pair annihilation inside the Universe's plasma due to their extremely small couplings. We demonstrate that for smaller couplings too, required for freeze-in process, a two component scalar dark matter model considered here could well be a viable candidate for FIMP. In this scenario, the Standard Model of particle physics is extended by two gauge singlet real scalars whose stability is protected by an unbroken $Z_{2}\times {Z'}_{2}$ symmetry and they are assumed to acquire no VEV after Spontaneous Symmetry Breaking. We explore the viable mass regions in the present two scalar DM model that is in accordance with the FIMP scenario. We also explore the upper limits of masses of the two components from the consideration of their self interactions., Comment: 31 pages LaTeX, 20 eps figures

We explore a two component dark matter model with a fermion and a scalar. In this scenario the Standard Model (SM) is extended by a fermion, a scalar and an additional pseudo scalar. The fermionic component is assumed to have a global ${\rm U(1)}_{\rm DM}$ and interacts with the pseudo scalar via Yukawa interaction while a $\mathbb{Z}_2$ symmetry is imposed on the other component -- the scalar. These ensure the stability of both the dark matter components. Although the Lagrangian of the present model is CP conserving, however the CP symmetry breaks spontaneously when the pseudo scalar acquires a vacuum expectation value (VEV). The scalar component of the dark matter in the present model also develops a VEV on spontaneous breaking of the $\mathbb{Z}_2$ symmetry. Thus the various interactions of the dark sector and the SM sector are progressed through the mixing of the SM like Higgs boson, the pseudo scalar Higgs like boson and the singlet scalar boson. We show that the observed gamma ray excess from the Galactic Centre, self-interaction of dark matter from colliding clusters as well as the 3.55 keV X-ray line from Perseus, Andromeda etc. can be simultaneously explained in the present two component dark matter model., Comment: 35 pages, 5 figures

Recent data from Reticulum II (RetII) require the energy range of the FermiLAT $\gamma$-excess to be $\sim$ $2-10$ GeV. We adjust our unified nonthermal Dark Matter (DM) model to accommodate this. We have two extra scalars beyond the Standard Model to also explain 3.55 keV X-ray line. Now the mass of the heavier of them has to be increased to lie around 250 GeV, while that of the lighter one remains at 7.1 keV. This requires a new seed mechanism for the $\gamma$-excess and new Boltzmann equations for the generation of the DM relic density. All concerned data for RetII and the X-ray line can now be fitted well and consistency with other indirect limits attained., Comment: 8 eps figures, 1 Table, 7 pages. The paper has been completely rewritten with additional references and discussions of indirect constraints from AMS-02 and ANTARES data. Basic results remain unchanged. Version accepted for publication in Europhysics Letters

We propose the existence of a hidden or dark sector besides the standard model (SM) of particle physics, whose members (both fermionic and bosonic) obey a local SU(2)$_{\rm H}$ gauge symmetry while behaving like a singlet under the SM gauge group. However, the fermiomic fields of the dark sector also possess another global U(1)$_{\rm H}$ symmetry which remains unbroken. The local SU(2)$_{\rm H}$ invariance of the dark sector is broken spontaneously when a scalar field in this sector acquires a vacuum expectation value (VEV) and thereby generating masses to the dark gauge bosons and dark fermions charged under the SU(2)$_{\rm H}$. The lightest fermion in this dark SU(2)$_{\rm H}$ sector can be a potential dark matter candidate. We first examine the viability of the model and constrain the model parameter space by theoretical constraints such as vacuum stability and by the experimental constraints such as PLANCK limit on relic density, LHC data, limits on spin independent scattering cross-section from dark matter direct search experiments etc. We then investigate the gamma rays from the pair annihilation of the proposed dark matter candidate at the Galactic Centre region. We also extend our calculations of gamma rays flux for the case of dwarf galaxies and compare the signatures of gamma rays obtained from these astrophysical sites., Comment: 33 pages, 16 figures, title changed, major revision

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles., Comment: 139 pages, Physics White Paper of the ICAL (INO) Collaboration, Contents identical with the version published in Pramana - J. Physics

In this thorough study we focus on the indirect detection of Dark Matter (DM) through the confrontation of unexplained galactic and extragalactic $\gamma$-ray signatures for a low mass DM model. For this, we consider a simple Higgs-portal DM model, namely, the inert Higgs doublet model (IHDM) where the Standard Model is extended with an additional complex SU(2)$_L$ doublet scalar. The stability of the DM candidate in this model, i.e., the lightest neutral scalar component of the extra doublet, is ensured by imposing discrete $\mathbb{Z}_2$ symmetry. The reduced-$\chi^2$ analysis with the theoretical, experimental and observational constraints suggests the best-fit value of DM mass in this model to be $\sim$ 63.5 GeV. We analyse the anomalous GeV $\gamma$-ray excess from Galactic Centre in light of the best-fit IHDM parameters. We further check the consistency of the best-fit IHDM parameters with the Fermi-LAT obtained limits on photon flux for 18 Milky Way dwarf spheroidal satellite galaxies (dSphs) known to be mostly dominated by DM. Also since the $\gamma$-ray signal from DM annihilation is assumed to be embedded within the extragalactic $\gamma$-ray background (EGB), the theoretical calculations of photon flux for the best-fit parameter point in the IHDM framework are compared with the Fermi-LAT results for diffuse and isotropic EGB for different extragalactic and astrophysical background parametrisations. We show that the low mass DM in IHDM framework can satisfactorily confront all the observed continuum $\gamma$-ray fluxes originated from galactic as well as extragalactic sources. The extensive analysis performed in this work is valid for any Higgs-portal model with DM mass in the ballpark of that considered in this work., Comment: 40 Pages, 21 eps Figures, 4 Tables; published in The Astrophysical Journal Supplement Series

A two component model of nonthermal dark matter is formulated to simultaneously explain the Fermi-LAT results indicating a $\gamma$-ray excess observed from our Galactic Centre in the 1-3 GeV energy range and the detection of an X-ray line at 3.55 keV from extragalactic sources. Two additional Standard Model singlet scalar fields $S_2$ and $S_3$ are introduced. These fields couple among themselves and with the Standard Model Higgs doublet $H$. The interaction terms among the scalar fields, namely $H$, $S_2$ and $S_3$, are constrained by the application of a discrete $\mathbb{Z}_2\times \mathbb{Z}^\prime_2$ symmetry which breaks softly to a remnant $\mathbb{Z}^{\prime \prime}_2$ symmetry. This residual discrete symmetry is then spontaneously broken through an MeV order vacuum expectation value $u$ of the singlet scalar field $S_3$. The resultant physical scalar spectrum has the Standard Model like Higgs as $\chi_{{}_{{}_1}}$ with $M_{\chi_{{}_{{}_1}}}\sim 125$ GeV, a moderately heavy scalar $\chi_{{}_{{}_2}}$ with $50 \,\,{\rm GeV} \leq M_{\chi_{{}_{{}_2}}}\leq 80\,\,{\rm GeV}$ and a light $\chi_{{}_{{}_3}}$ with $M_{\chi_{{}_{{}_3}}} \sim 7$ keV. There is only tiny mixing between $\chi_{{}_{{}_1}}$ and $\chi_{{}_{{}_2}}$ as well as between $\chi_{{}_{{}_1}}$ and $\chi_{{}_{{}_3}}$. The lack of importance of domain wall formation in the present scenario from the spontaneous breaking of the discrete symmetry ${\mathbb{Z}_2^{\prime\prime}}$, provided $u\leq 10$ MeV, is pointed out. We find that our proposed two component dark matter model is able to explain successfully both the above mentioned phenomena $-$ the Fermi-LAT observed $\gamma$-ray excess (from the $\chi_{{}_{{}_2}} \rightarrow {\rm b} \bar{\rm b}$ decay mode) and the observation of the X-ray line (from the decay channel $\chi_{{}_{{}_3}}\rightarrow\gamma \gamma$) by the XMM-Newton observatory., Comment: 11 eps Figures, 2 Tables, 32 Pages. Minor addition in Abstract. Inclusion in Section 1 of discussion of earlier attempts to explain the concerned phenomena by astrophysical processes. Extension of discussion in Section 6 to the case of a steeper dark matter density profile. Results unchanged. Version accepted for publication in JHEP

If the three types of active neutrinos possess different maximum attainable velocities and the neutrino eigenstates in the velocity basis are different from those in the flavour (and mass) basis then this will induce a flavour oscillation in addition to the normal mass flavour oscillation. Here we study such an oscillation scenario in three neutrino framework including also the matter effect and apply our results to demonstrate its consequences for long baseline neutrinos. We also predict the possible signatures in terms of yields in a possible long baseline neutrino experiment., Comment: 20 pages, 5 figures, Accepted in Modern Physics Letters A

Recent study of gamma rays originating from the region of galactic centre has confirmed an anomalous $\gamma$-ray excess within the energy range 1-3 GeV. This can be explained as the consequence of pair annihilation of a 31-40 GeV dark matter into $b \bar b$ with thermal annihilation cross-section $\sigma v \sim 1.4-2.0 \times 10^{-26}~\rm{cm^3/s}$. In this work we revisit the Inert Doublet Model (IDM) in order to explain this gamma ray excess. Taking the lightest inert particle (LIP) as a stable DM candidate we show that a 31-40 GeV dark matter derived from IDM will fail to satisfy experimental limits on dark matter direct detection cross-section obtained from ongoing direct detection experiments and is also inconsistent with LHC findings. We show that a singlet extended inert doublet model can easily explain the reported $\gamma$-ray excess which is as well in agreement with Higgs search results at LHC and other observed results like DM relic density and direct detection constraints., Comment: 17 pages, 4 figures

In this work we consider a model for particle dark matter where an extra inert Higgs doublet and an additional scalar singlet is added to the Standard Model (SM) Lagrangian. The dark matter candidate is obtained from only the inert doublet. The stability of this one component dark matter is ensured by imposing a $Z_2$ symmetry on this additional inert doublet. The additional singlet scalar has a vacuum expectation value (VEV) and mixes with the Standard Model Higgs doublet resulting in two CP even scalars $h_1$ and $h_2$. We treat one of these scalars, $h_1$, to be consistent with the SM Higgs like boson of mass around 125 GeV reported by the LHC experiment. These two CP even scalars affect the annihilation cross-section of this inert doublet dark matter resulting in a larger dark matter mass region that satisfies the observed relic density. We also investigate the $h_1 \rightarrow \gamma\gamma$ and $h_1 \rightarrow \gamma Z$ processes and compared these with LHC results. This is also used to constrain the dark matter parameter space in the present model. We find that the dark matter candidate in the mass region $\frac {m_1} {2} < m_H < m_W$ GeV ($m_1 = 125$ GeV, mass of $h_1$) satisfies the recent bound from LUX direct detection experiment., Comment: 21 Pages, 5 Figures, 1 Table

We promote the idea of multi-component Dark Matter (DM) to explain results from both direct and indirect detection experiments. In these models as contribution of each DM candidate to relic abundance is summed up to meet WMAP/Planck measurements of $\Omega_{\rm DM}$, these candidates have larger annihilation cross-sections compared to the single-component DM models. This results in larger $\gamma$-ray flux in indirect detection experiments of DM. We illustrate this fact by introducing an extra scalar to the popular single real scalar DM model. We also present detailed calculations for the vacuum stability bounds, perturbative unitarity and triviality constraints on this model. As direct detection experimental results still show some conflict, we kept our options open, discussing different scenarios with different DM mass zones. In the framework of our model we make an interesting observation: The existing direct detection experiments like CDMS II, CoGeNT, CRESST II, XENON 100 or LUX together with the observation of excess low energy $\gamma$-ray from Galactic Centre and Fermi Bubble by FGST already have the capability to distinguish between different DM halo profiles., Comment: 43 Pages, 14 Figures and 5 Tables; text and reference modified

We explore a fermionic dark matter model with a possible extension of Standard Model (SM) of particle physics into two Higgs doublet model. Higgs doublets couple to the singlet fermionic dark matter (FDM) through a non renormalisable coupling providing a new physics scale. We explore the viability of such dark matter candidate and constrain the model parameter space by collider serach, relic density of DM, direct detection measurements of DM-nucleon scattreing cross-section and with the experimentally obtained results from indirect search of dark matter., Comment: 22 pages, 17 new png figures, Title changed, new references added, major revision

In this paper, we examine the cosmological viability of a slow moving galileon field in a potential. The Lagrangian $\cal{L}$ $ =-\frac{1}{2}g^{\mu\nu}\pi_{;\mu}\pi_{;\nu} +\frac{G^{\mu\nu}}{2M^2}\pi_{;\mu}\pi_{;\nu}$ respects the galileon symmetry in curved space time. We carry out detailed investigations of the underlying dynamics of this Lagrangian with Einstein-Hilbert term and a potential. We demonstrate that the model can give rise to a viable ghost free late time acceleration of universe. Furthermore we study the cosmological perturbation of the model and see that the model gives different BBN constraints at early times. We also carry out the observational analysis of the model and use observational data from growth, Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO) and Cosmic Microwave Background (CMB) to constrain the parameters of the theory., Comment: 7 pages, 7 figures

Recently there has been a hint of a gamma-ray line at 130 GeV originated from the galactic centre after the analysis of the Fermi-LAT satellite data. Being monochromatic in nature, it rules out the possibility of having its astrophysical origin and there has been a speculation that this line could be originated from dark matter annihilation. In this work, we propose a two component dark matter scenario where an extension of the Standard model by an inert Higgs doublet and a gauge singlet scalar concocted with $\rm {Z_2 \times Z^{\prime}_2}$ symmetry, is considered. We find that our scenario can not only explain the 130 GeV gamma-ray line through dark matter annihilation but also produce the correct dark matter relic density. We have used the Standard Model Higgs mass around 125 GeV as intimated by the LHC data.., Comment: 35 pages, 15 figures, 6 tables, Accepted for publication in JCAP

We propose a two parameter generalization for the dark energy equation of state (EOS) $w_X$ for thawing dark energy models which includes PNGB, CPL and Algebraic thawing models as limiting cases and confront our model with the latest observational data namely SNe Ia, OHD, CMB, BOSS data. Our analysis reveals that the phantom type of thawing dark energy is favoured upto $2 \sigma$ confidence level. These results also show that thawing dark energy EOS is not unique from observational point of view. Though different thawing dark energy models are not distinguishable from each other from best-fit values (upto $2\sigma$ C.L.s) of matter density parameter ($\Omega_m^0$) and hubble parameter ($H_0$) at present epoch, best-fit plots of linear growth of matter perturbation ($f$) and average deceleration parameter ($q_{\rm av}$); the difference indeed reflects in best-fit variations of thawing dark energy EOS, model-independent geometrical diagnostics like the statefinder pair $\{r,s\}$ and $Om3$ parameter. We are thus led to the conclusion that unlike the standard observables ($\Omega_m^0$, $H_0$, $f$, $q_{\rm av}$), the model-independent parameters ($r,s,Om3$) and the variations of EOS (in terms of $w_X-w_X'$ plots) serve as model discriminators for thawing dark energy models., Comment: 13 pages LaTeX, 14 postscript figures. Accepted for publication in MNRAS

We consider the lightest supersymmetric particle (LSP), neutralino in minimal anomaly mediated supersymmetry breaking model (mAMSB) to be a possible candidate for weakly interacting massive particles (WIMP) or cold dark matter and investigate its direct and indirect detections. The theoretically allowed supersymmetric parametric space for such a model along with the recent bounds from LHC is constrained by the WMAP results for relic densities. The spin independent and spin dependent scattering cross sections for dark matter off nucleon are thus constrained from the WMAP results. They are found to be within the allowed regions of different ongoing direct detection experiments. The annihilation of such dark matter candidates at the galactic centre produce different standard model particles such as gamma rays, neutrinos etc. In this work, we calculate the possible fluxes of these $\gamma$-rays and neutrinos coming from the direction of the galactic centre (and its neighbourhood) at terrestrial or satellite borne detectors. The calcutated $\gamma$-ray flux is compared with the observational results of HESS experiment. The neutrino flux of different flavours from the galactic centre and at different locations away from the galactic centre produced by WIMP annihilation in this model are also obtained for four types of galactic dark matter halo profiles. The detection prospects of such $\nu_\mu$ coming from the direction of the galactic centre at the ANTARES under sea detector are discussed in terms of muon signal yield from these muon neutrinos. Both the gamma and neutrino signals are estimated for four different dark matter halo profiles., Comment: 34 pages LaTeX, 36 postscript figures; Text and figures modified, new figures added; version published in J. Phys. G

From the analysis of Supernova Ia data alongwith Observational Hubble Data (OHD) and Baryon Acoustic Oscillation (BAO) data, we attempt to find out the nature of a scalar potential that may be responsible for the Dark Energy of the universe. We demonstrate that in order to explain the varying dark energy equation of state ($\omega_X(z)$) as obtained in a model independent way from the analyses of observational data, we need to invoke a quintom scalar field having a "quintessence" part for $\omega_X(z) > -1$ and a "phantom" part for $\omega_X(z) < -1$. We consider a Gaussian type potential for these scalar fields and compare the dark energy equation of state derived from such potential with the one computed from the data analysis., Comment: 13 pages, 5 eps figures