We investigate the relic abundance of asymmetric Dark Matter particles that were in thermal equilibrium in the early universe. The standard analytic calculation of the symmetric Dark Matter is generalized to the asymmetric case. We calculate the asymmetry required to explain the observed Dark Matter relic abundance as a function of the annihilation cross section. We show that introducing an asymmetry always reduces the indirect detection signal from WIMP annihilation, although it has a larger annihilation cross section than symmetric Dark Matter. This opens new possibilities for the construction of realistic models of MeV Dark Matter. * wrns@xju.edu.cn † drees@th.physik.uni-bonn.de ‡ xuelei@cosmology.bao.ac.cn * In other words, we define the "particle" to be the one with the larger density, if an asymmetry exists.
We investigate the relic density n χ of non-relativistic long-lived or stable particles χ in cosmological scenarios in which the temperature T is too low for χ to achieve full chemical equilibrium. The case with a heavier particle decaying into χ is also investigated. We derive approximate solutions for n χ (T ) which accurately reproduce numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the χ number density. However, it does give the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures.
We investigate the relic abundance of asymmetric Dark Matter particles in quintessence model with a kination phase. The analytic calculation of the asymmetric Dark Matter in the standard cosmological scenario is extended to the nonstandard cosmological scenario where we specifically discuss the quintessence model with a kination phase. We found that the enhancement of Hubble rate changes the relic density of particles and anti-particles. We use the present day Dark Matter abundance to constrain the Hubble rate in quintessence model with a kination phase for asymmetric Dark Matter. *
Using the Modules for Experiments in Stellar Astrophysics code, we investigate the influences of irradiation on ultra-compact X-ray binary (UCXB) evolution. Although the persistent UCXBs have short orbital periods which result in high irradiation flux, the irradiation hardly affects the evolution of persistent sources because the WDs in these binaries have large masses which lead to very low irradiation depth. The irradiation has a significant effect on the transient sources during outburst phase. At the beginning of the outburst, high X-ray luminosity produces high radiation flux, which results in the significant expansion of WD. Then, the irradiation triggers high masstransfer rates, which can last several days for the transient sources with WDs whose masses are larger than ∼ 0.015M ⊙ or several hundred years for these sources with WDs whose masses are less than ∼ 0.012M ⊙ . The observed three persistent UCXBs, XTE J0929-314, 4U 1916-05 and SWIFT J1756.9-2508, may belong to the latter.
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