SÉMINAIRE DU GRECO
"Velocity Dispersion Effects in the Linear Growth of Cosmic Structures" |
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Oliver Piattella |
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We discuss solutions of Vlasov-Einstein equation for collisionless particles (representing dark matter) on a flat Friedmann background Universe. Taking into account the dark matter velocity dispersion, we show that, after decoupling from the primordial plasma, the dark matter phase-space indicator $Q = \rho/(\sigma_{1D}^2)^{3/2}$ remains constant during the expansion of the universe, prior to structure formation. At the linear perturbations level we show that the velocity dispersion gives rise to an extra term, in the evolution equation for the density contrast, which behaves as a sort of effective pressure perturbation, thereby permitting to define a physical Jeans length for collisionless matter as a function of the primordial phase-space indicator $Q$, i.e $a\lambda_J = (5\pi/3G)^{1/2}Q^{-1/3}\rho_{dm}^{-1/6}$. |
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lundi 6 mai 2013 - 11:00 Salle des séminaires François Arago, Institut d'Astrophysique de Paris |
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