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Article
Report number arXiv:1005.2051
Title Spherical Collapse in Chameleon Models
Author(s) Brax, Ph ; Rosenfeld, R ; Steer, D A
Publication 2010
Imprint 13 May 2010
Note Comments: matches printed version
Comments: matches printed version
In: JCAP 08 (2010) 033
DOI 10.1088/1475-7516/2010/08/033
Subject category Astrophysics and Astronomy
Abstract 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 depends on the initial comoving size of the inhomogeneity.
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