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.

The relic abundance of asymmetric Dark Matter particles in the scalar-tensor model is analyzed in this article. We extend the numeric and analytic calculation of the relic density of the asymmetric Dark Matter in the standard cosmological scenario to the nonstandard cosmological scenario. We focus on the scalar-tensor model. Hubble expansion rate is changed in the nonstandard cosmological scenario. This leaves its imprint on the relic density of Dark Matter particles. In this article we investigate to what extent the asymmetric Dark Matter particle's relic density is changed in the scalar-tensor model.We use the observed present day Dark Matter abundance to find the constraints on the parameter space in this model. *

We investigate the relic density n χ of non-relativistic long-lived or stable particles χ in non-standard cosmological scenarios. We calculate the relic abundance starting from arbitrary initial temperatures of the radiationdominated epoch, and derive the lower bound on the initial temperature T 0 ≥ m χ /23, assuming that thermally produced χ particles account for the dark matter energy density in the universe; this bound holds for all χ annihilation cross sections. We also investigate cosmological scenarios with modified expansion rate. Even in this case an approximate formula similar to the standard one is capable of predicting the final relic abundance correctly. Choosing the χ annihilation cross section such that the observed cold dark matter abundance is reproduced in standard cosmology, we constrain possible modifications of the expansion rate at T ∼ m χ /20, well before Big Bang Nucleosynthesis.

We discuss the relic abundance of asymmetric Dark Matter particles in modified cosmological scenarios where the Hubble rate is changed with respect to the standard cosmological scenario. The modified Hubble rate leaves its imprint on the relic abundance of asymmetric Dark Matter particles if the asymmetric Dark Matter particles freeze-out in this era. For generality we parameterize the modification of the Hubble rate and then calculate the relic abundance of asymmetric Dark Matter particles and anti-particles.We found the abundances for the Dark Matter particles and anti-particles are enhanced in the modified cosmological models. The indirect detection signal is possible for the asymmetric Dark Matter particles due to the increased annihilation rate in the modified cosmological models. Applying Planck data, we find the constraints on the parameters of the modified cosmological models.

We propose an analytic treatment for computing the relic abundances of non-relativistic particles whose annihilation rate at chemical decoupling is increased by Sommerfeld enhancement. We find approximate rational functions that closely fit the thermal average of Sommerfeld-enhanced cross sections in the massless limit of force carriers for s-and p-wave annihilations. We demonstrate that, with the approximate thermally-averaged cross sections implemented, the standard analytic method for the final relic abundances provides accuracy to within 1% even for the case of Sommerfeld enhancement.