A dynamical-systems analysis of f(R,ℛ) hybrid metric-Palatini gravity shows no global attractors in the cosmological phase space and only two classes of fixed-point scale factors, one of which predicts a jerk parameter near 4.47.
On the evolution of density perturbations in f(R) theories of gravity
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abstract
In the context of $f(R)$ theories of gravity, we study the evolution of scalar cosmological perturbations in the metric formalism. Using a completely general procedure, we find the exact fourth-order differential equation for the matter density perturbations in the longitudinal gauge. In the case of sub-Hubble modes, the expression reduces to a second-order equation which is compared with the standard (quasi-static) equation used in the literature. We show that for general $f(R)$ functions the quasi-static approximation is not justified. However, for those functions adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it provides a correct description for the evolution of perturbations.
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gr-qc 1years
2019 1verdicts
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Cosmological phase space of generalized hybrid metric-Palatini theories of gravity
A dynamical-systems analysis of f(R,ℛ) hybrid metric-Palatini gravity shows no global attractors in the cosmological phase space and only two classes of fixed-point scale factors, one of which predicts a jerk parameter near 4.47.