• Kamakshya Prasad Modak

      Articles written in Pramana – Journal of Physics

    • A two-component dark matter model with real singlet scalars confronting GeV 𝛾-ray excess from galactic centre and Fermi bubble

      Debasish Majumdar Kamakshya Prasad Modak Subhendu Rakshit

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      We propose a two-component dark matter (DM) model, each component of which is a real singlet scalar, to explain results from both direct and indirect detection experiments. We put the constraints on the model parameters from theoretical bounds, PLANCK relic density results and direct DM experiments. The 𝛾-ray flux is computed from DM annihilation in this framework and is then compared with the Fermi-LAT observations from galactic centre region and Fermi bubble.

    • Neutron star cooling via axion emission by nucleon–nucleon axion bremsstrahlung


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      Neutron stars generally cool 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 the 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 and 1.8 solar masses) and by including the effect of axion emission for different axion masses ($m_{a} = 10^{−5}, 10^{−3}$ and $10^{−2} eV$) 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 gave an upper bound on axion mass limits $m_{a} \leq 10^{−3}$ eV which implies that the axion decay constant $f_{a} \geq 0.6×10^{10}$ GeV.

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