20,366 research outputs found
Non-linear clustering during the BEC dark matter phase transition
Spherical collapse of the Bose-Einstein Condensate (BEC) dark matter model is
studied in the Thomas Fermi approximation. The evolution of the overdensity of
the collapsed region and its expansion rate are calculated for two scenarios.
We consider the case of a sharp phase transition (which happens when the
critical temperature is reached) from the normal dark matter state to the
condensate one and the case of a smooth first order phase transition where
there is a continuous conversion of "normal" dark matter to the BEC phase. We
present numerical results for the physics of the collapse for a wide range of
the model's space parameter, i.e. the mass of the scalar particle
and the scattering length . We show the dependence of the transition
redshift on and . Since small scales collapse earlier and
eventually before the BEC phase transition the evolution of collapsing halos in
this limit is indeed the same in both the CDM and the BEC models. Differences
are expected to appear only on the largest astrophysical scales. However, we
argue that the BEC model is almost indistinguishable from the usual dark matter
scenario concerning the evolution of nonlinear perturbations above typical
clusters scales, i.e., . This provides an analytical
confirmation for recent results from cosmological numerical simulations [H.-Y.
Schive {\it et al.}, Nature Physics, {\bf10}, 496 (2014)].Comment: 11 pages. Final version to appear in EPJ
Polytropic equation of state and primordial quantum fluctuations
We study the primordial Universe in a cosmological model where inflation is
driven by a fluid with a polytropic equation of state . We calculate the dynamics of the scalar factor and build a
Universe with constant density at the origin. We also find the equivalent
scalar field that could create such equation of state and calculate the
corresponding slow-roll parameters. We calculate the scalar perturbations, the
scalar power spectrum and the spectral index.Comment: 16 pages, 4 figure
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