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arXiv · 2212.13825

The effective Equation of State in Palatini $f(R)$ cosmology

S. Camera·S. Capozziello·L. Fatibene·A. Orizzonte
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Abstract

We investigate how the cosmological Equation of State can be used for scrutinizing extended theories of gravity, in particular, the Palatini $f(R)$ gravity. Specifically, the approach consists, at first, in investigating the effective Equation of State produced by a given model. Then, the inverse problem can also be considered in view of determining which models are compatible with a given effective Equation of State. We consider and solve some cases and show that, for example, power-law models are (the only models) capable of transforming barotropic Equations of State into effective barotropic ones. Moreover, the form of Equation of State is preserved (only) for $f(R)=R$, as expected. In this perspective, modified Equations of State are a feature capable of distinguishing Extended Gravity with respect to General Relativity. We also investigate quadratic and non-homogeneous effective Equations of State showing, in particular, that they contain the Starobinsky model and other ones.

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S. Camera, S. Capozziello, L. Fatibene, A. Orizzonte. 2022-12-28. The effective Equation of State in Palatini $f(R)$ cosmology. https://doi.org/10.1140/epjp%2Fs13360-023-03676-0

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