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Evolution of the phase-space density and the Jeans scale for dark matter derived from the Vlasov-Einstein equation | | Oliver F. Piattella
; Davi C. Rodrigues
; Júlio C. Fabris
; José A. de Freitas Pacheco
; | | Date: |
15 Jun 2013 | | Abstract: | Solutions of Vlasov-Einstein equation for collisionless particles
(representing dark matter) are discussed in the context of a flat Friedmann
universe. It is shown that, after decoupling from the primordial plasma, the
dark matter phase-space density indicator Q remains constant during the
expansion of the universe, prior to structure formation. This well known result
is valid for non-relativistic particles and is not "observer dependent" as in
solutions derived from the Vlasov-Poisson system. In the linear regime, the
inclusion of velocity dispersion effects permits to define the physical Jeans
length for collisionless matter as a function of the primordial phase-space
density indicator Q, i.e., lambda_J = (5pi/G)^(1/2) Q^(-1/3) rho^(-1/6). The
comoving Jeans wavenumber at matter-radiation equality is smaller by a factor
of 2-3 than the comoving wavenumber due to free streaming, contributing to the
cut-off of the density fluctuation power spectrum at the lowest scales. The
physical differences between these two scales are discussed. For dark matter
particles of mass equal to 200 GeV, the derived Jeans mass is 4.3 x 10^(-6)
solar masses. | | Source: | arXiv, 1306.3578 | | Services: | Forum | Review | PDF | Favorites | |
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