Department of Physics

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Author: search.filters.author.Mishra, Madhukar

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    Emission properties of non-rotating neutron stars with magnetic field using modified TOV equations
    (Springer, 2024-07) Mishra, Madhukar; Sarkar, Tapomoy Guha
    Emission properties of the Astrophysical objects such as Neutron Stars are found using mass, pressure profile and thermal cooling rate. In this current work, we determine the cooling rate of spherically symmetric neutron star as a function of time and distance from the star’s centre using NSCool code. Here we first find the mass, pressure and baryon number density profile of the non-rotating neutron stars using modified Tolman-Oppenheimer-Volkoff (TOV) system of equations in the presence of intense magnetic field. We used here a constant value of magnetic field and a distance dependent magnetic field in TOV equations to obtain the profile. We employ three different equation of states to solve the TOV equations by assuming that the core of Neutron Stars is composed of a hadronic matter. By employing above profile, we obtain the cooling rate with and without magnetic field to examine the effect of magnetic field for three different equations of states. Observed temperature of a few Neutron Stars have also been plotted along with calculated values for comparison. Finally, emissivity of axions as a dark matter candidates has been calculated as a result of the nucleon Bremsstrahlung mechanism with and without magnetic field.
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    Profile and cooling rate of non-rotating magnetars using strange quark matter equation of states
    (Springer, 2024-07) Mishra, Madhukar
    Various astrophysical objects like Neutron Stars, Magnetars, Blackholes, etc. have been extensively studied in the last few decades in order to predict and analyze observations pertaining to such compact objects. Despite of multiple attempts, the exact nature of the matter located inside the core of the above compact objects is still an open problem in Astrophysics. In this work, we attempt to find the profile of spherically symmetric non-rotating Neutron Stars by assuming that the core of the Neutron Star is made up of strange quark matter. The calculation has also been carried out with a core consisting of non-strange quark matter for comparison. We also include the impact of the magnetic field on the profile of the Neutron Stars employing a modified Tolmann-Oppenheimer-Volkoff system of equations. Using the profile thus obtained, the Neutron Star cooling rate with time and as a function of the radius has also been calculated with and without magnetic field effects using NSCool code. Two approaches namely; a fixed value of the magnetic field and a more realistic distance-dependent magnetic field obtained by using a fitted eight-order polynomial have been used in the current calculation. Finally, we plot the Neutron cooling rate with and without magnetic fields by using the different equations of states (EOS) along with corresponding observed data for a few neutron Stars.
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    Cooling of neutron stars through emission of neutrinos and photons: effects of modified gravity and magnetic field using tov equations
    (2024-12) Mishra, Madhukar
    The existence of dark matter has long been extensively studied in the past few decades. In this study, we investigate the emission of neutrinos and photons from neutron stars (NSs) by employing the modified theory of gravity and the corresponding Tolman-Oppenheimer-Volkoff (TOV) system of equations. The extreme matter density and magnetic field inside the NSs provide a unique laboratory for studying fundamental physics, including the interplay between gravity and quantum field effects. The impact of a strong magnetic field has also been incorporated into the corresponding TOV equations. We here attempt to see how neutrinos and photons emissions from these compact objects are impacted by the modified TOV equations due to modified theory of gravity; f(R,T) gravity or scalar-tensor theory and strong magnetic fields. Our analysis focuses on how these modifications influence the structure, cooling, and photon/neutrino luminosities of NS. We computed the surface temperature of NSs for normal Einstein gravity and modified gravity theories with and without magnetic field for three EoSs; namely APR, FPS and SLY. On comparison of our predicted values of surface temperature with the observed surface temperature for three NSs, we find that modified gravity along with inside magnetic field-based predictions shows reasonable agreement with the corresponding observed values.
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    Conversion of Emitted Axionic Dark Matter to Photons for Non-Rotating Magnetized Neutron Stars
    (ARXIV, 2024-02) Sarkar, Tapomoy Guha; Mishra, Madhukar
    We attempt to find the impact of a modified Tolman Oppenheimer Volkoff (TOV) system of equations on the luminosities of direct photons, neutrinos and axions for a particular axion mass in the presence of a magnetic field. We employ two different equation of states (EoSs) namely APR and FPS to generate the profiles of mass and pressure for spherically symmetric and non-rotating Neutron stars (NSs). We then compute the axions and neutrino emission rates by employing the Cooper-pair-breaking and formation process (PBF) in the core using the NSCool code. We also examine the possibility of axion to photon conversion in the magnetosphere of NSs. Furthermore, we investigate the impact of the magnetic field on the actual observables, such as the energy spectrum of axions and axion-converted photon flux for three different NSs. Our comparative study indicates that axions energy spectrum and axion-converted photon flux changes significantly due to an intense magnetic field.
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    Thermal evolution and axion emission properties of strongly magnetized neutron stars
    (Springer, 2024-03) Sarkar, Tapomoy Guha; Mishra, Madhukar
    Emission properties of compact astrophysical objects such as Neutron stars (NSs) are associated with crucial astronomical observables. In the current work, we obtain the mass, pressure profiles of the non-rotating NSs using the modified Tolman Oppenheimer Volkoff (TOV) system of equations in the presence of intense magnetic field. We obtain the profiles by using a specific distance-dependent magnetic field in the modified TOV equations. We employ three different equations of states (EoS) to solve the TOV equations by assuming the core of NSs comprises a hadronic matter. Employing the above profiles, we determine the cooling rates of spherically symmetric NSs as a function of time with and without including the magnetic field using the NSCool code. We have also determined the cooling rates as a function of radius for three different NSs. Furthermore, we determine the luminosity of neutrinos, axions, and photons emitting from the NSs in the presence and absence of a magnetic field for an axion mass 16 meV and three different EoS. Our comparative study indicates that the cooling rate and luminosities of neutrinos, axions, and photons change significantly due to the impact of the strong magnetic field. We also find that due to the magnetic field, the axion mass bound increases slightly compared to without a magnetic field.
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    X-ray emission spectrum for axion-photon conversion in magnetospheres of strongly magnetized neutron stars
    (ARXIV, 2024-03) Sarkar, Tapomoy Guha; Mishra, Madhukar
    Detecting axionic dark matter (DM) could be possible in an X-ray spectrum from strongly magnetized neutron stars (NSs). We examine the possibility of axion-photon conversion in the magnetospheres of strongly magnetized NSs. In the current work, we investigate how the modified Tolman Oppenheimer Volkoff (TOV) system of equations (in the presence of a magnetic field) affects the energy spectrum of axions and axions-converted photon flux. We have considered the distance-dependent magnetic field in the modified TOV equations. We employ three different equations of states (EoSs) to solve these equations. We obtain the axions emission rate by including the Cooper-pair-breaking formation process (PBF) and Bremsstrahlung process in the core of NSs using the NSCool code. We primarily focus on three NSs: PSR B0531+21, PSR J0538+2817, and one Magnificient seven (M7) star RXJ 1856.5-3754. We further investigate the impact of the magnetic field on the actual observables, such as axion`s energy spectrum and axion-photon flux. We also compare our calculated axion-photon flux from all available archival data from PN+MOS+Chandra. Our predicted axion-photon flux values as a function of axion`s energy closely follow the experimentally archival data, which allows us to put bounds on the axion`s mass for the three different EoS.13
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    pQCD approach to charmonium regeneration in QGP at the LHC
    (Elsevier, 2016-03) Mishra, Madhukar
    We analyze the applicability of perturbative QCD (pQCD) approach to the issue of recombination at the Large Hadron Collider (LHC), and calculate the recombination cross section for recombination to form as a function of temperature. The charmonium wavefunction is obtained by employing a temperature dependent phenomenological potential between the pair. The temperature dependent formation time of charmonium is also employed in the current work. A set of coupled rate equations is established which incorporates color screening, gluonic dissociation, collisional damping and recombination of uncorrelated pair in the quark–gluon plasma (QGP) medium. The final suppression, thus determined as a function of centrality is compared with the ALICE experimental data at both mid and forward rapidity and CMS experimental data at mid rapidity obtained from the Large Hadron Collider (LHC) at center of mass energy .
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    psi(2S) enhancement in p–Pb collision as an indication of quark–gluon plasma formation at the Large
    (IOP, 2018-02) Mishra, Madhukar
    Proton–nucleus collisions serve as an important baseline for the understanding and interpretation of the nucleus–nucleus collisions. These collisions have been employed to characterize the cold nuclear matter effects at SPS and Relativistic Heavy-Ion Collider energies for the past several years, as it was thought that quark–gluon plasma (QGP) is not formed in such collisions. However, at the Large Hadron Collider (LHC), there seems a possibility that QGP is formed during proton–lead (p–Pb) collisions. In this work, we have derived an expression for gluon induced excitation of to , using pNRQCD, and show that the relative enhancement of vis-à-vis , especially at high pT, gives further indication that the QGP is indeed formed in p–Pb collisions at the most central collisions at LHC energy. and suppression effects seen at ALICE are also qualitatively explained.
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    Centrality and transverse momentum dependent suppression of and in p–Pb and Pb–Pb collisions at the CERN Large Hadron Collider
    (Springer, 2019-02) Mishra, Madhukar
    Deconfined QCD matter in heavy-ion collisions has been a topic of paramount interest for many years. Quarkonia suppression in heavy-ion collisions at the relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) experiments indicate the quark-gluon plasma (QGP) formation in such collisions. Recent experiments at LHC have given indications of hot matter effect in asymmetric p–Pb nuclear collisions. Here, we employ a theoretical model to investigate the bottomonium suppression in Pb–Pb at , 5.02 TeV, and in p–Pb at TeV center-of-mass energies under a QGP formation scenario. Our present formulation is based on an unified model consisting of suppression due to color screening, gluonic dissociation along with the collisional damping. Regeneration due to correlated pairs has also been taken into account in the current work. We obtain here the net bottomonium suppression in terms of survival probability under the combined effect of suppression plus regeneration in the deconfined QGP medium. We mainly concentrate here on the centrality, and transverse momentum, dependence of and states suppression in Pb–Pb and p–Pb collisions at mid-rapidity. We compare our model predictions for and suppression with the corresponding experimental data obtained at the LHC energies. We find that the experimental observations on and dependent suppression agree reasonably well with our model predictions
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    Bottomonium suppression in PbPb collisions at energies available at the CERN Large Hadron Collider
    (APS, 2021-09) Mishra, Madhukar
    High energy collisions are the laboratories within our reach to study strongly interacting matter under extreme temperatures. In the present study, we use a quarkonia suppression scheme to explain the bottomonium production at the two energies available at the CERN Large Hadron Collider. We employ echo-qgp to model the (3+1)-dimensional relativistic viscous hydrodynamic evolution of the medium. Bottomonia produced in the early stage dissociates due to color screening, gluonic dissociation, and collisional damping in addition to shadowing as an initial state effect. In the color screening mechanism, the temperature from hydrodynamics is used to find the screening radii at each centrality and rapidity. The shadowing effect utilizes the parton distribution functions obtained from the CT14 global analysis and shadowing factors from EPPS16. A lattice QCD based equation of state from the Wuppertal-Budapest Collaboration has been used. The experimental values of pion (π+) spectra were used to constrain the initial conditions of the dynamics. The bottomonium suppression is determined as a function of centrality, transverse momentum, and rapidity for Υ(1S) and Υ(2S) states at the LHC energies of 2.76 and 5.02TeV. We find a fairly good agreement between our theoretically calculated survival probability and the measured nuclear modification factor (RAA) at the two energies.