We propose a dark-matter (DM) admixed density-dependent equation of state where the fermionic DM interacts with the nucleons via Higgs portal. Presence of DM can hardly influence the particle distribution inside neutron star (NS) but can significantly affect the structure as well as equation of state (EOS) of NS. Introduction of DM inside NS softens the equation of state. We explored the effect of variation of DM mass and DM Fermi momentum on the NS EOS. Moreover, DM-Higgs coupling is constrained using dark matter direct detection experiments. Then, we studied cooling of normal NSs using APR and DD2 EOSs and DM admixed NSs using dark-matter modified DD2 with varying DM mass and Fermi momentum. We have done our analysis by considering different NS masses. Also DM mass and DM Fermi momentum are varied for fixed NS mass and DM-Higgs coupling. We calculated the variations of luminosity and temperature of NS with time for all EOSs considered in our work and then compared our calculations with the observed astronomical cooling data of pulsars namely Cas A, RX J0822-43, 1E 1207-52, RX J0002+62, XMMU J17328, PSR B1706-44, Vela, PSR B2334+61, PSR B0656+14, Geminga, PSR B1055-52 and RX J0720.4-3125. It is found that APR EOS agrees well with the pulsar data for lighter and medium mass NSs but cooling is very fast for heavier NS. For DM admixed DD2 EOS, it is found that for all considered NS masses, all chosen DM masses and Fermi momenta agree well with the observational data of PSR B0656+14, Geminga, Vela, PSR B1706-44 and PSR B2334+61. Cooling becomes faster as compared to normal NSs in case of increasing DM mass and Fermi momenta. It is infered from the calculations that if low mass super cold NSs are observed in future that may support the fact that heavier WIMP can be present inside neutron stars.
We study the cascade of Hawking emission spectrum from the event horizon in presence of one loop back reaction effect in a black hole background. The spacetime is taken here is the modified Schwarzschild one. The analysis shows that it is possible to decrease the sparsity with the decrease in black hole mass. Moreover, at some particular value of mass one has a continuous radiation cascade. This result is completely new and quite different from the usual one. An estimation of the mass for continuous one is also found. We see that the value is of the Planck mass order. In this process it is observed that under a physical background, below a particular value of the mass the Hawking radiation must stop and we have a remnant. This was absent in the earlier analysis.
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 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 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 aLIGO.
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 eV, 10 −3 eV, 10 −2 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 B0656+14, Geminga and PSR B1055-52 and finally give an upper bound on axion mass limits m a ≤ 10 −3 eV which implies that the axion decay constant f a ≥ 0.6 × 10 10 GeV.A neutron star (NS) [1, 2] with a typical radius of 10-12 km and generally having a mass range of 1-2 solar mass (M ) is formed as an aftermath of a massive supernova explosion. A neutron star can be cooled principally by the emission of photons and neutrinos. It is also conjectured that the emission of axion from a neutron star may contribute to its cooling process in addition to photon and neutrino emissions. Axions [3,4] are pseudo Nambu-Goldstone bosons which are introduced to circumvent the strong CP problem [5] that refers to the presence of CP violation term in QCD Lagrangian [6] arising from the non-Abelian nature of QCD gauge symmetry. The Peccei-Quinn (PQ) solution [5] of strong CP problem results in the prediction of new particle namely axion. The axion which is a Goldstone boson that arises out of the PQ solution where an anomalous chiral symmetry U(1) A [7] is introduced and is spontaneously broken at the PQ energy scale, is an interesting candidate in addressing several aspects of cosmology and particle physics such as dark matter in the Universe. Since the axion have tiny couplings with photons, nucleons and electrons, they can be produced inside a neutron star through the nucleon-nucleon axion bremsstrahlung process N + N → N + N + a, where N is a nucleon (proton or neutron) and "a" denotes axion. As mentioned earlier, while the energy loss is considered to be mostly due to photon and neutrino emission, the emission of axion from the late stages of the star such as the supernova or neutron star can also contribute in considerable measure to the process of their cooling. Here we have considered that neutron star is the source of the axions. But axions can be emitted from the other astrophysical sources like the sun, white dwarf, supernova, red giant, globular clusters etc. ...
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. 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.