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f(R) Gravity and Chameleon Theories | | Philippe Brax
; Carsten van de Bruck
; Anne-Christine Davis
; Douglas J. Shaw
; | | Date: |
20 Jun 2008 | | Abstract: | We analyse f(R) modifications of Einstein’s gravity as dark energy models in
the light of their connection with chameleon theories. Formulated as
scalar-tensor theories, the f(R) theories imply the existence of a strong
coupling of the scalar field to matter. This would violate all experimental
gravitational tests on deviations from Newton’s law. Fortunately, the existence
of a matter dependent mass and a thin shell effect allows one to alleviate
these constraints. The thin shell condition also implies strong restrictions on
the cosmological dynamics of the f(R) theories. As a consequence, we find that
the equation of state of dark energy in the recent past is constrained to be
extremely close to -1. We also examine the potential effects of f(R) theories
in the context of the Eot-wash experiments. We show that the requirement of a
thin shell for the test bodies is not enough to guarantee a null result on
deviations from Newton’s law. The constraints which we deduce also forbid any
measurable deviation of the dark energy equation of state from -1. All in all,
we find that both cosmological and laboratory tests imply that f(R) models are
almost coincident with a Lambda-CDM model at the background level. | | Source: | arXiv, 0806.3415 | | Services: | Forum | Review | PDF | Favorites | |
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