Brax, Ph.Rosenfeld, Rogério [UNESP]Steer, D. A.2013-09-302014-05-202013-09-302014-05-202010-08-01Journal of Cosmology and Astroparticle Physics. Bristol: Iop Publishing Ltd, n. 8, p. 26, 2010.1475-7516http://hdl.handle.net/11449/24339We 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.26engmodified gravitydark energy theoryArtigo10.1088/1475-7516/2010/08/033WOS:000283575000007Acesso restrito