MG11 
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Cosmological viability of f(R)-gravity as an ideal fluid and its compatibility with a matter dominated phase

We show that f(R)-gravity can, in general, give rise to cosmological viable models compatible with a matter-dominated epoch evolving into a late accelerated phase. We discuss the various representations of f(R)-gravity as an ideal fluid or a scalar-tensor gravity theory, taking into account conformal transformations. We point out that mathematical equivalence does not correspond, in several cases, to the physical equivalence of Jordan frame and Einstein frame. Finally, we show that wide classes of f(R)-gravity models, including matter and accelerated phases, can be phenomenologically reconstructed by means of observational data. In principle, any popular quintessence models could be "reframed" as an f(R)-gravity model.

Dark Energy and Dark Matter as Curvature Effects

Higher order theories of gravity have recently attracted a lot of interest as alternative candidates to explain the observed cosmic acceleration, the flatness of the rotation curves of spiral galaxies and other relevant astrophysical phenomena. Very likely, what we call “dark matter” and “dark energy” are nothing else but signals of the breakdown of General Relativity at large scales. Furthermore, PPN-paramete,s deduced from Solar System experiments do not exclude, a priori, the possibility that such theories could give small observable effects also at these scales. We review these results giving the basic ingredients of such an approach.