Adding Dark Matter to the Standard Model

Detailed and redundant measurements of dark matter properties have recently become available. To describe the observations we consider scalar, vector and sterile neutrino dark matter models. A model with vector dark matter is consistent with all current observations.

Pairwise Velocity Statistics of Dark Halos

We have accurately evaluated the halo pairwise velocity dispersion and the halo mean streaming velocity in the LCDM model (the fiat ω0 = 0.3 model) using a set of high-resolution N-body simulations. Based on the simulation results, we have developed a model for the pairwise velocity dispersion of halos. Our model agrees with the simulation results over all scales we studied. We have also tested the model of Sheth et al. for the mean streaming motion of halos derived from the pair-conservation equation. We found that their model reproduces the simulation data very well on large scale, but under-predicts the streaming motion on scales r < 10 h-1 Mpc. We have introduced an empirical relation to improve their model. These improved models are useful for predicting the redshift correlation functions and the redshift power spectrum of galaxies if the halo occupation number model, e.g. the cluster weighted model, is given for the galaxies.

Effective field theory approach to lepto-philic self-conjugate dark matter

We study self-conjugate dark matter(DM)particles interacting primarily with Standard Model(SM)leptons in an effective field theoretical framework.We consider SM gauge-invariant effective contact interactions between Majorana fermion,real scalar and real vector DM with leptons by evaluating the Wilson coefficients appropriate for interaction terms up to dimension 8,and obtain constraints on the parameters of the theory from the observed relic density,indirect detection observations and from the DM-electron scattering cross-sections in direct detection experiments.Low energy LEP data has been used to study sensitivity in the pair production of low mass(≤80 GeV)DM particles.Pair production of DM particles of mass≥50 GeV in association with mono-photons at the proposed ILC has rich potential to probe such effective operators.

Constraints on dark matter annihilation and decay from the isotropic gamma-ray background

We study the constraints on dark matter（DM） annihilation/decay from the Fermi-LAT Isotropic Gamma-Ray Background（IGRB） observation.We consider the contributions from both extragalactic and galactic DM components.For DM annihilation,the evolution of extragalactic DM halos is taken into account.We find that the IGRB annihilation constraints under some DM subhalo models can be comparable to those derived from the observations of dwarf spheroidal galaxies and CMB.We also use the IGRB results to constrain the parameter regions accounting for the latest AMS-02 electron-positron anomaly.We find that the majority of DM annihilation/decay channels are strongly disfavored by the latest Fermi-LAT IGRB observation;only DM decays to μ^＋μ^-and 4μ channels may be valid.

Contradiction between strong lensing statistics and a feedback solution to the cusp/core problem

Standard cosmology has many successes on large scales, but faces some fundamental difficulties on small, galactic scales. One such difficulty is the cusp/core problem. High resolution observations of the rotation curves for dark matter domi- nated low surface brightness （LSB） galaxies imply that galactic dark matter halos have a density profile with a flat central core, whereas N-body structure formation simula- tions predict a divergent （cuspy） density profile at the center. It has been proposed that this problem can be resolved by stellar feedback driving turbulent gas motion that erases the initial cusp. However, strong gravitational lensing prefers a cuspy density profile for galactic halos. In this paper, we use the most recent high resolution observations of the rotation curves of LSB galaxies to fit the core size as a function of halo mass, and compare the resultant lensing probability to the observational results for the well defined combined sample of the Cosmic Lens All-Sky Survey （CLASS） and Jodrell Bank/Very Large Array Astrometric Survey （JVAS）. The lensing probabilities based on such density profiles are too low to match the observed lensing in CLASS/JVAS. High baryon densities in the galaxies that dominate the lensing statis- tics can reconcile this discrepancy, but only if they steepen the mass profile rather than making it more shallow. This places contradictory demands upon the effects of baryons on the central mass profiles of galaxies.

A Remark on Using Gravitational Lensing Probability as a Probe of the Central Regions of CDM Halos

We calculate the gravitational lensing probabilities by cold dark matter (CDM) halos with different density profiles, and compare them with current observations from the Cosmic Lens All-Sky Survey (CLASS) and the Jodrell-Bank VLA Astrometric Survey (JVAS). We find that the lensing probability is dramatically sensitive to the clumping of the dark matter, or quantitatively, the concentration parameter. We also find that our predicted lensing probabilities in most cases show inconsistency with the observations. It is argued that high lensing probability may not be an effective tool for probing the statistical properties of inner structures of dark matter halos.