Non-Baryonic Dark Matter in Cosmology

This paper is a broad-band review of the current status of non-baryonic dark matter research. I start with a historical overview of the evidences of dark matter existence, then I discuss how dark matter is distributed from small scale to large scale, and I then verge the attention to dark matter nature: dark matter candidates and their detection. I finally discuss some of the limits of the $\Lambda$CDM model, with particular emphasis on the small scale problems of the paradigm.Comment: 62 pages; 58 figure

Numerical tests of dynamical friction in gravitational inhomogeneous systems

In this paper, I test by numerical simulations the results of Del Popolo & Gambera (1998),dealing with the extension of Chandrasekhar and von Neumann's analysis of the statistics of the gravitational field to systems in which particles (e.g., stars, galaxies) are inhomogeneously distributed. The paper is an extension of that of Ahmad & Cohen (1974), in which the authors tested some results of the stochastic theory of dynamical friction developed by Chandrasekhar & von Neumann (1943) in the case of homogeneous gravitational systems. It is also a continuation of the work developed in Del Popolo (1996a,b), which extended the results of Ahmad & Cohen (1973), (dealing with the study of the probability distribution of the stochastic force in homogeneous gravitational systems) to inhomogeneous gravitational systems. Similarly to what was done by Ahmad & Cohen (1974) in the case of homogeneous systems, I test, by means of the evolution of an inhomogeneous system of particles, that the theoretical rate of force fluctuation d F/dt describes correctly the experimental one, I find that the stochastic force distribution obtained for the evolved system is in good agreement with the Del Popolo & Gambera (1998) theory. Moreover, in an inhomogeneous background the friction force is actually enhanced relative to the homogeneous case.Comment: 12 pages; 2 encapsulated figures. Aatronomy and Astrophysics, in prin

Profiles of dark-matter haloes at high redshift

I study the evolution of haloes density profiles as a function of time in the SCDM and LCDM cosmologies. Following Del Popolo et al. (1999), I calculate the concentration parameter c=r_v/a and study its time evolution. For a given halo mass, I find that c(z) ~1/(1+z) both in the LCDM and SCDM cosmology, in agreement with Bullock et al. (1999) analytic model and N-body simulations. In both models, a(z) is roughly constant. The present model predicts a stronger evolution of c(z) with respect to Navarro et al. (1997) model. Finally I show some consequences of the result on galaxy modelling.Comment: 14 pages, 3 encapsulated figures. Accepted by MNRA