Chameleon stars supported by a cosmological scalar field

Abstract

Starting from the assumption that the present accelerated expansion of the Universe is driven by a chameleon scalar field, the function describing a direct coupling between the matter content of the Universe and the scalar field is derived from cosmological considerations. In progressing from cosmology towards astrophysical scales, this function is used to estimate the influence that such nonminimal coupling may have on the properties of usual (polytropic) stars whose matter can interact directly with the cosmological chameleon. It is shown that in order to obtain sizes and masses of compact configurations supported by the chameleon scalar field comparable to those of usual stars, it is necessary to assume that the pressure of the matter content of the Universe is substantially different from zero. The question of a possible manifestation of the effects of the nonminimal coupling in laboratory experiments is also discussed.

14 pages, 1 figure, minor corrections to content, appendix and references added, version published in PRD

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