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Journal of Cosmology and Astroparticle Physics 08 (2010) 033
Spherical collapse in chameleon models
P. Brax, R. Rosenfeld, D.A. Steer1

We study the gravitational collapse of an overdensity of nonrelativistic matter under the action of gravity and a chameleon scalar field. We show that the spherical collapse model is modified by the presence of a chameleon field. In particular, we find that even though the chameleon effects can be potentially large at small scales, for a large enough initial size of the inhomogeneity the collapsing region possesses a thin shell that shields the modification of gravity induced by the chameleon field, recovering the standard gravity results. We analyse the behaviour of a collapsing shell in a cosmological setting in the presence of a thin shell and find that, in contrast to the usual case, the critical density for collapse in principle depends on the initial comoving size of the inhomogeneity.
1 :  APC - UMR 7164 - AstroParticule et Cosmologie
Physique/Physique des Hautes Energies - Théorie
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