A Study Of Constraints On Dark Matter By Neutron Stars Probe

In chapter 1, we introduce the properties and characteristics, and the classifi-cation as well as the inner structure of the NS. Then, we compare the differences between the NS and the strange quark star, and discuss the constrains of obser-vations on the NS, including the maximum mass, mass-radius relation, thermal radiation, and limit rotation.The existence of dark matter in the universe is demonstrated via the observa-tions of galactic rotation curves, collisions in clusters of galaxies, gravitational lens effects, and the simulations of large scale structures in the universe. In chapter 2, we introduce three dark matter profiles of the Milky Way (NFW profile, Einasto profile, and Burkert profile), candidates of dark matter, and the status of detection (direct detection, indirect detection, and collider detection). Direct detection shows a strict upper limit of WIMP-nucleon scattering cross section, as the upgrading of underground detector and the improvement of cross section sensitivity.Weakly interacting massive particle (WIMP) is one of the most popular candi-dates of dark matter at present. In chapter 3, we study the effect of dark matter WIMP on the thermal evolution of NS (common NS and strange quark star). We consider the accretions of WIMPs onto the NS, the thermalization of WIMPs, and the annihilation and heating processes of WIMPs in the thermal evolution of the NS. The surface temperature plateau Tcq～ρdm1/4 common NS or strange quark star will appear at t≥106.5 yr, once the heating of dark matter annihilation equilibrates the cooling of surface photon emission. The minimum annihilation cross section of nonthermally produced WIMPs which is constrained by the thermal radiation of the NS ranges from 10-61 to 10-57 cm2. The surface temperature of the NS reaches a value of 3 x 105 K at 10-4 pc from the Galactic center for the NFW profile. However, the WIMP-nucleon cross section (elastic or inelastic) is as low as～10-45 cm2, which is 2 orders of magnitude lower than the current experimental limit. Hence, the NS can probe much smaller WIMP-nucleon cross section.Millicharged (MC) particle is now another concerned candidate of dark matter. MC particle is beyond the standard model of particle physics, it has electric charge e’= ee, where t is any real number and ε< 1. MC particle has an obvious impact on the standard picture of the Universe, including the expansion rate of the Universe, the baryon-to-photon ratio in the early universe, the anisotropy power spectrum of the cosmic microwave background, and the origin of seeds for galactic and cluster magnetic fields. At present, the constraints on the mass and the charge of MC particles are mainly from laboratory bounds, universe bounds, and stellar evolution bounds. In chapter 4, the limits on the mass and the charge of MC particles are shown via the extreme rotational period of the NS. We consider an extra slow-down torque due to the accretions of MC particles onto the NS based on magnetic dipole radiation and the G J current in the rotational period evolution of the NS. We have constrained the mass and the charge of MC particles, using the longest observed period 8.51 s of normal pulsars at 2.72 x 108 yr as the cutoff of the period evolution. For a canonical NS of M= 1.4 M0 and R= 10 km, we have shown an upper limit of MC particles, (1GeV/m) ×ε< 2.52 ×10-2/cos2θ which is compatible with experimental and observational bounds.