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      Fermionic Light Dark Matter particles and the New Physics of Neutron Stars

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          Abstract

          Dark Matter constitutes most of the matter in the presently accepted cosmological model for our Universe. The extreme conditions of ordinary baryonic matter, namely high density and compactness, in Neutron Stars make these objects suitable to gravitationally accrete such a massive component provided interaction strength between both, luminous and dark sectors, at current experimental level of sensitivity. We consider several different DM phenomenological models from the myriad of those presently allowed. In this contribution we review astrophysical aspects of interest in the interplay of ordinary matter and a fermionic light Dark Matter component. We focus in the interior nuclear medium in the core and external layers, i.e. the crust, discussing the impact of a novel dark sector in relevant stellar quantities for (heat) energy transport such as thermal conductivity or emissivities.

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          Cooling neutron star in the Cassiopeia~A supernova remnant: Evidence for superfluidity in the core

          According to recent results of Ho & Heinke (2009) and Heinke & Ho (2010), the Cassiopeia A supernova remnant contains a young neutron star which has carbon atmosphere and shows noticeable decline of the effective surface temperature. We report a new (November 2010) Chandra observation which confirms the previously reported decline rate. The decline is naturally explained if neutrons have recently become superfluid (in triplet-state) in the NS core, producing a splash of neutrino emission due to Cooper pair formation (CPF) process that currently accelerates the cooling. This scenario puts stringent constraints on poorly known properties of NS cores: on density dependence of the temperature \(T_\mathrm{cn}(\rho)\) for the onset of neutron superfluidity [\(T_\mathrm{cn}(\rho)\) should have a wide peak with maximum \(\approx (7-9)\times 10^8\) K], on the reduction factor \(q\) of CPF process by collective effects in superfluid matter (\(q > 0.4\)), and on the intensity of neutrino emission before the onset of neutron superfluidity (30--100 times weaker than the standard modified Urca process). This is serious evidence for nucleon superfluidity in NS cores that comes from observations of cooling NSs.
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            Thermal emission of neutron stars with internal heaters

            Using 1D and 2D cooling codes we study thermal emission from neutron stars with steady state internal heaters of various intensities and geometries (blobs or spherical layers) located at different depths in the crust. The generated heat tends to propagate radially, from the heater down to the stellar core and up to the surface; it is also emitted by neutrinos. In local regions near the heater the results are well described with the 1D code. The heater's region projects onto the stellar surface forming a hot spot. There are two heat propagation regimes. In the first, conduction outflow regime (realized at heat rates \(H_0 \lesssim 10^{20}\) erg cm\(^{-3}\) s\(^{-1}\) or temperatures \(T_\mathrm{h} \lesssim 10^9\) K in the heater) the thermal surface emission of the star depends on the heater's power and neutrino emission in the stellar core. In the second, neutrino outflow regime (\(H_0 \gtrsim 10^{20}\) erg cm\(^{-3}\) s\(^{-1}\) or \(T_\mathrm{h} \gtrsim 10^9\) K) the surface thermal emission becomes independent of heater's power and the physics of the core. The largest (a few per cent) fraction of heat power is carried to the surface if the heater is in the outer crust and the heat regime is intermediate. The results can be used for modeling young cooling neutron stars (prior to the end of internal thermal relaxation), neutron stars in X-ray transients, magnetars and high-\(B\) pulsars, as well as merging neutron stars.
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              Author and article information

              Journal
              18 October 2017
              Article
              10.1017/pasa.2017.38
              1710.06866
              fa48eeda-9727-4892-910b-0658614ad23f

              http://arxiv.org/licenses/nonexclusive-distrib/1.0/

              History
              Custom metadata
              Publications of the Astronomical Society of Australia (PASA), Vol. 34, e043, 11 pages (2017)
              12 pages, 7 figures, 1 table. Review contribution
              astro-ph.HE hep-ph nucl-th

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