857 research outputs found
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 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
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