Papers by Umananda Dev Goswami
A three dimensional structure of a solar wind effect on the intensity variation of cosmic rays ha... more A three dimensional structure of a solar wind effect on the intensity variation of cosmic rays has been investigated by using the regression analysis method in this paper. The solar wind effect discussed here is represented by the regression coefficients between the intensity variation of cosmic rays and the solar wind velocity. The data of cosmic ray intensity used in the analysis have been measured by the multi directional muon telescope (GRAPES3) at Ooty in southern India during the period from 2000 to 2007. The data of solar wind velocity have been referred to the ACE level 2 data set. In order to examine the three dimensional structure of the solar wind effect, we have classified the data of the cosmic ray intensity into 12 directional components. From this analysis, we have clearly confirmed the existence of the solar wind effect on the intensity vari- ation of cosmic rays and the regression coefficients around ¡ 0:001%=(km=s) have been obtained. By the analysis with the data ...
galprop.stanford.edu
The huge cosmic ray background and extremely low signal primarily limit the sensitivity of the EA... more The huge cosmic ray background and extremely low signal primarily limit the sensitivity of the EAS experiments for UHE γ-ray astronomy. However the GRAPES-3 high density EAS array has a unique advantage for UHE γ-ray astronomy as it uses muon detection for cosmic ray back ground rejection using a large area (560m 2 ) compact tracking muon detector. To increase background rejection efficiency further, it was decided to increase the muon detector area to 1120m 2 by constructing another muon detector similar to the existing one. Here we present the results of the Monte Carlo simulation study of the rejection efficiency and sensitivity detection of CRAB nebula with the expanded muon detector. The simulation results show that the CRAB nebula can be seen unambiguously in 1 year with the expanded muon detector.
We present here a new approach for signature ol Higgs Ixwon prcKiuclion in ultra high energy cosm... more We present here a new approach for signature ol Higgs Ixwon prcKiuclion in ultra high energy cosmic ray (UHE('R) interactions using ihc thermoficid theory The idea is the decay of Higgs bosons that are produced through bubble formation due to vacuum excitation in an UHE(R collision with air nuclei. We develop a model of hadronic interaction based on the GENC^L code of the UA5 experiment of TERN and ('ORSIKA code (Karlsruhe report), incorporating a fraction of energy transfei to bubble formation by phase transition due to vacuum excitation and subsequent multiparticle prtxluction via conversion of Higgs boson to heavy fermion pairs Such events are expected to have high multiplicity and excess muons Wc compare the muon multiplicity distribution with and without this effect for different fractions of energy transfer to vacuum It has been found that ihc Higgs boson production mechanism has significant effect starting from-lO'^cV
Isotropic gamma ray flux is expected as a result of interactions of ultra high energy cosmic rays... more Isotropic gamma ray flux is expected as a result of interactions of ultra high energy cosmic rays (E > 10 19 eV) with the cosmic microwave background radiation and/or the annihilation/decay of topological defects. On the other hand, diffuse gamma ray flux from the galactic plane is expected as a result of interactions of cosmic rays with the interstellar matter. Thus these gamma rays are one of the possible probes to study cosmic rays and their source distribution. We search for diffuse gamma rays with the GRAPES-3 air shower array. It is a high-density array of 1 m 2 area plastic scintillation detectors and the large area (560 m 2) shielded muon detectors, and it is located at Ooty in the southern India. High statistics with such large area muon detectors help us to distinguish gamma ray showers with hadron showers. Based on the observations from March 2000 to July 2004 we obtained a new upper limit of the ratio of isotropic gamma rays to cosmic rays in the energy range of 20 – ...
alpha.sci.osaka-cu.ac.jp, 2009
A.Oshima∗, SRDugad∗, T.Fujii, UDGoswami∗, SKGupta∗, Y.Hayashi, N.Ito, P.Jagadeesan∗, A.Jain∗, ... more A.Oshima∗, SRDugad∗, T.Fujii, UDGoswami∗, SKGupta∗, Y.Hayashi, N.Ito, P.Jagadeesan∗, A.Jain∗, S.Karthikeyan∗, S.Kawakami, H.Kojima, T.Matsuyama, M.Minamino, H.Miyauchi, PKMohanty∗, SDMorris∗, PKNayak∗, T.Nonaka, S.Ogio, ...
arXiv (Cornell University), Jan 24, 2011
A model of induced gravity with Higgs potential is analysed for the FLRW cosmology. Conditions of... more A model of induced gravity with Higgs potential is analysed for the FLRW cosmology. Conditions of acceleration and signatures for the primeval universe along with the inflation are discussed. It is shown that the scalar-field excitations act quintessentially within effective pressure terms for a negative deceleration parameter. The violation of energy conditions and primeval acceleration appears naturally in the present model in view of the notions for inflationary universe with the avoidance of the Big Bang singularity.
Physics of the Dark Universe, Aug 1, 2023
In this work we investigate a Schwarzschild-type black hole that is corrected by the Generalized ... more In this work we investigate a Schwarzschild-type black hole that is corrected by the Generalized Uncertainty Principle (GUP) and possesses topological defects within the framework of Bumblebee gravity. Our focus is on the thermodynamic characteristics of the black hole, such as temperature, entropy and heat capacity, which vary as functions of the horizon radius, and also on shadow as an optical feature. Our investigation reveals significant changes in the thermodynamic behavior of the black hole due to violations of Lorentz symmetry, GUP corrections, and the presence of monopoles. However, the shadow of the black hole is unaffected by violations of Lorentz symmetry. In addition, we provide a limit on the parameters of Lorentz symmetry violation and topological defects based on a classical test involving the precession of planetary orbits and the advancement of perihelion in the solar system.
Physics of the Dark Universe, Dec 1, 2022
We study the gravitational wave echoes from the static and spherically symmetric compact stars in... more We study the gravitational wave echoes from the static and spherically symmetric compact stars in f (R, T) gravity metric formalism. In this study, to describe the matter of compact stars we use the MIT Bag model and the color-flavor-locked (CFL) equations of state (EoSs). Solving the hydrostatic equilibrium equations i.e., the modified TOV equations in this gravity, we obtain different stellar models. The mass-radius profiles for such stellar configurations are eventually discussed. The stability of these configurations are then analysed using different model parameters. From the solutions of TOV equations, we check the compactness of such objects. It is found that similar to the unrealistic EoS, i.e. the stiffer form of the MIT Bag model, under some considerations the realistic interacting quark matter CFL EoS can give stellar structures which are compact enough to possess a photon sphere outside the stellar boundary and hence can echo GWs. The obtained echo frequencies are found to lie in the range of 39-55 kHz. Moreover, we show that for different parametrizations of the gravity theory, the structure of stars and also the echo frequencies differ significantly. Further, we constrain the pairing constant value β from the perspective of emission of echo frequencies. It shows that for the stiffer MIT Bag model β ≥ −2.474 and for the CFL phase with massless quark condition β ≥ −0.873, whereas for the massive case β ≥ −0.813.
Journal of Cosmology and Astroparticle Physics, Jun 1, 2022
We have obtained the Generalized Uncertainty Principle (GUP) corrected de Sitter and anti-de Sitt... more We have obtained the Generalized Uncertainty Principle (GUP) corrected de Sitter and anti-de Sitter black hole solutions in bumblebee gravity with a topological defect. We have calculated the scalar, electromagnetic and gravitational quasinormal modes for the both vanishing and non-vanishing effective cosmological constant using Padé averaged sixth order WKB approximation method. Apart from this, the time evolutions for all three perturbations are studied, and quasinormal modes are calculated using the time domain profile. We found that the first order and second order GUP parameters α and β, respectively have opposite impacts on the quasinormal modes. The study also finds that the presence of a global monopole can decrease the quasinormal frequencies and the decay rate significantly. On the other hand, Lorentz symmetry violation has noticeable impacts on the quasinormal frequencies and the decay rate. We have studied the greybody factors, power spectrum and sparsity of the black hole with the vanishing effective cosmological constant for all the three perturbations. The presence of Lorentz symmetry breaking and the GUP parameter α decrease, while other GUP parameter β and the presence of global monopole increase the probability of Hawking radiation to reach the spatial infinity. The presence of Lorentz violation can make the black holes less sparse, while the presence of a global monopole can increase the sparsity of the black holes. Moreover, we have seen that the black hole area quantization rule is modified by the presence of Lorentz symmetry breaking.
arXiv (Cornell University), Nov 5, 2022
Galactic rotation curve is a powerful indicator of the state of the gravitational field within a ... more Galactic rotation curve is a powerful indicator of the state of the gravitational field within a galaxy. Flatness of these curves implies the linear increase of mass to have constant velocity with the radial distance. In this paper, we focus on the possibility of explaining the flatness of observed rotation curves of spiral galaxies without postulating the existence of dark matter in the framework of f (R, T) gravity where the gravitational Lagrangian is written by an arbitrary function of R, the Ricci scalar and of T , the trace of stress-energy tensor Tµν. We derive the gravitational field equations in this gravity theory for the static spherically symmetric spacetime and solve the equations for metric coefficients using a specific model that has minimal coupling between matter and geometry. The orbital motion of a massive test particle moving in a stable circular orbit is considered and the behaviour of tangential velocity in the halo region with the help of the considered model is studied. The linear variation with distance of the interaction mass generated due to matter-geometry coupling successfully explains the galactic dynamics without the existence of dark matter at large distances from the galactic core.
arXiv (Cornell University), May 16, 2023
We investigate the impact of the axionic coupling parameter on the bending angle of light and the... more We investigate the impact of the axionic coupling parameter on the bending angle of light and the shadow cast by slowly rotating black holes in Chern-Simons modified gravity. We utilize the Ishihara et al. method to derive the deflection angle of light for an observer and source located at finite distances from a lens object in an asymptotically flat spacetime, using the Gauss-Bonnet theorem. The deflection angle exhibits an increasing trend up to a certain point, followed by a decrease as a function of the impact parameter, with the presence of the axion matter field causing the observed increase. Additionally, we calculate the Einstein ring radius as a direct application of the weak deflection angle. We also investigate the effect of the axion matter field on the time delay of light and analyze its impact on the shadow cast by slowly rotating black holes. Our findings reveal a significant effect of the axionic coupling parameter on the black hole's shadow.
arXiv (Cornell University), Mar 10, 2023
Astroparticle Physics, Jul 1, 2018
We have studied the distribution patterns of lateral density, arrival time and angular position o... more We have studied the distribution patterns of lateral density, arrival time and angular position of Cherenkov photons generated in Extensive Air Showers (EASs) initiated by γ-ray, proton and iron primaries incident with various energies and at various zenith angles. This study is the extension of our earlier work [1] to cover a wide energy range of ground based γ-ray astronomy with a wide range of zenith angles (≤ 40 •) of primary particles, as well as the extension to study the angular distribution patterns of Cherenkov photons in EASs. This type of study is important for distinguishing the γ-ray initiated showers from the hadronic showers in the ground based γ-ray astronomy, where Atmospheric Cherenkov Technique (ACT) is being used. Importantly, such study gives an insight on the nature of γ-ray and hadronic showers in general. In this work, the CORSIKA 6.990 simulation code is used for generation of EASs. Similarly to the case of Ref.[1], this study also revealed that, the lateral density and arrival time distributions of Cherenkov photons vary almost in accordance with the functions: ρ ch (r) = ρ0 e −βr and t ch (r) = t0e Γ/r λ respectively by taking different values of the parameters of functions for the type, energy and zenith angle of the primary particle. The distribution of Cherenkov photon's angular positions with respect to shower axis shows distinctive features depending on the primary type, its energy and the zenith angle. As a whole this distribution pattern for the iron primary is noticeably different from those for γ-ray and proton primaries. The value of the angular position at which the maximum number of Cherenkov photons are concentrated, increases with increase in energy of vertically incident primary, but for inclined primary it lies within a small value (≤ 1 •) for almost all energies and primary types. No significant difference in the results obtained by using the high energy hadronic interaction models, viz., QGSJETII and EPOS has been observed.
European Physical Journal C, Dec 1, 2020
In this paper, we have introduced a new f (R) gravity model as an attempt to have a model with mo... more In this paper, we have introduced a new f (R) gravity model as an attempt to have a model with more parametric control, so that the model can be used to explain the existing problems as well as to explore new directions in physics of gravity, by properly constraining it with recent observational data. Here basic aim is to study the properties of Gravitational Waves (GWs) in this new model. In f (R) gravity metric formalism, the model shows the existence of scalar degree of freedom as like other f (R) gravity models. Due to this reason, there is a scalar mode of polarization of GWs present in the theory. This polarization mode exists in a mixed state, of which one is transverse massless breathing mode with non-vanishing trace and the other is massive longitudinal mode. The longitudinal mode being massive, travels at speed less than the usual tensor modes found in General Relativity (GR). Moreover, for a better understanding of the model, we have studied the potential and mass of scalar graviton in both Jordan frame and Einstein frame. This model can pass the solar system tests and can explain primordial and present dark energy. Also, we have put constraints on the model. It is found that the correlation function for the third mode of polarization under certain mass scale predicted by the model agrees well with the recent data of Pulsar Timing Arrays. It seems that this new model would be useful in dealing with different existing issues in the areas of astrophysics and cosmology.
Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021), Jul 30, 2021
Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021), Aug 1, 2021
The GRAPES-3 extensive air shower (EAS) array located at Ooty is equipped with 400 plastic scinti... more The GRAPES-3 extensive air shower (EAS) array located at Ooty is equipped with 400 plastic scintillator detectors spread over an area of 25,000 m 2 and a muon telescope of area 560 m 2 built with 3,712 proportional counters. One of its principal objectives is to measure the primary cosmic ray energy spectrum in the TeV-PeV energy region. The response of the photo-multiplier tubes (PMTs) used in the plastic scintillator detectors becomes nonlinear at densities > 50 particles-m −2 in large EAS. We describe a technique to correct for the nonlinearity of these PMTs, thereby extending the dynamic range of the detectors for observed particle densities up to ∼5000 particlesm −2. The details of the technique will be presented.
Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021), Jul 30, 2021
Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021), Jul 30, 2021
Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021), Jul 29, 2021
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Papers by Umananda Dev Goswami