Effect of Neutrinos on Angular Momentum of Dark Matter Halo

Massive neutrinos are expected to affect the large-scale structure formation,including the major component of solid substances,dark matter halos.How halos are influenced by neutrinos is vital and interesting,and angular momentum(AM)as a significant feature provides a statistical perspective for this issue.Exploring halos from TianNu N-body cosmological simulation with the co-evolving neutrino particles,we obtain some concrete conclusions.First,by comparing the same halos with and without neutrinos,in contrast to the neutrino-free case,over 89.71%of halos have smaller halo moduli,over 71.06%have smaller particle-mass-reduced(PMR)AM moduli,and over 95.44%change their orientations of less than 0°.65.Moreover,the relative variation of PMR modulus is more visible for low-mass halos.Second,to explore the PMR moduli of halos in dense or sparse areas,we divide the whole box into big cubes,and search for halos within a small spherical cell in a single cube.From the two-level divisions,we discover that in denser cubes,the variation of PMR moduli with massive neutrinos decreases more significantly.This distinction suggests that neutrinos exert heavier influence on halos'moduli in compact regions.With massive neutrinos,most halos(86.60%)have lower masses than without neutrinos.

Probing dynamics of dark energy with latest observations

We examine the validity of the ACDM model and probe the dynamics of dark energy with the latest astronomical observations. Using the Ore（z） diagnosis, we find that various kinds of observational data are in tension within the ACDM framework. We then allow for dynamics of dark energy and investigate the constraint on dark energy parameters. We find that for two different kinds of parametri- sations of the equation of state parameter w, a combination of current data mildly favours an evolving w, although the significance is not sufficient for it to be supported by Bayesian evidence. A forecast of the DESI survey shows that the dynamics of dark energy could be detected at the 7σ confidence level and would be decisively supported by Bayesian evidence, if the best-fit model of w derived from current data is the true model.

Probing the dark side of the Universe with weak gravitational lensing effects

Arising from gravitational deflections of light rays by large-scale struc- tures in the Universe, weak-lensing effects have been recognized as one of the most important probes in cosmological studies. In this paper, we review the main progress in weak-lensing analyses, and discuss the challenges in future investigations aiming to understand the dark side of the Universe with unprecedented precisions.

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.

The moment generating function of pairwise velocity in the context of redshift space distortion

We study the connections between the pairwise velocity moment generating function G(k_(‖),r)and redshift space distortion(RSD)modeling.Here k_(‖)is the Fourier wavevector parallel to the line of sight,and r is the pair separation vector.We demonstrate its usage by two examples.(1)Besides the known relations between G and the RSD power spectrum(and the correlation function),we propose a new RSD statistics Ps(k_(‖),r_(丄))whose connection to G is convenient to evaluate numerically.(2)We then develop a fast method to numerically evaluate G,and apply it to a high resolution N-body simulation.We find that G(ln G)shows complicated dependence on k_(‖)beyond the linear and quadratic dependencies.This not only shows inaccuracy in some existing models and identifies sources of inaccuracy but also provides possible ways of improving the RSD modeling.Consequently,more comprehensive investigations on G are needed to fully explore the usage of G in RSD modeling.

Influence of baryons on the spatial distribution of matter:higher order correlation functions

Physical processes involving baryons could leave a non-negligible imprint on the distribution of cosmic matter.A series of simulated data sets at high resolution with identical initial conditions are employed for count-in-cell analysis,including one N-body pure dark matter run,one with only adiabatic gas and one with dissipative processes.Variances and higher order cumulants Sn of dark matter and gas are estimated.It is found that physical processes with baryons mainly affect distributions of dark matter at scales less than 1 h-1 Mpc.In comparison with the pure dark matter run,adiabatic processes alone strengthen the variance of dark matter by～10%at a scale of 0.1 h-1 Mpc,while the Sn parameters of dark matter only mildly deviate by a few percent.The dissipative gas run does not differ much from the adiabatic run in terms of variance for dark matter,but renders significantly different Sn parameters describing the dark matter,bringing about a more than 10%enhancement to S3 at 0.1 h-1 Mpc and z=0 and being even larger at a higher redshift.Distribution patterns of gas in two hydrodynamical simulations are quite different.Variance of gas at z=0 decreases by～30%in the adiabatic simulation but by～60%in the nonadiabatic simulation at 0.1 h-1 Mpc.The attenuation is weaker at larger scales but is still obvious at～10 h-1 Mpc.Sn parameters of gas are biased upward at scales 〈～4 h-1 Mpc,and dissipative processes show an～84%promotion at z=0 to S3 at 0.1 h-1 Mpc in contrast with the～7%change in the adiabatic run.The segregation in clustering between gas and dark matter could have dramatic implications on modeling distributions of galaxies and relevant cosmological applications demanding fine details of matter distribution in a strongly nonlinear regime.