Dynamics of Linear Perturbations in the hybrid metric-Palatini gravity

Abstract

In this work we focus on the evolution of the linear perturbations in the novel hybrid metric-Palatini theory achieved by adding a $f(\mathcal{R})$ function to the gravitational action. Working in the Jordan frame, we derive the full set of linearized evolution equations for the perturbed potentials and present them in the Newtonian and synchronous gauges. We also derive the Poisson equation, and perform the evolution of the lensing potential, ${\Phi }_{+}$, for a model with a background evolution indistinguishable from $\Lambda$CDM. In order to do so, we introduce a designer approach that allows to retrieve a family of functions $f(\mathcal{R})$ for which the effective equation of state is exactly $w_{\text{eff}}=-1$. We conclude, for this particular model, that the main deviations from standard General Relativity and the Cosmological Constant model arise in the distant past, with an oscillatory signature in the ratio between the Newtonian potentials, $\Phi$ and $\Psi$.

arXiv comment11 pages, 3 figures. Version 3 with minor changes to match version accepted by PRD

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• New class of hybrid metric-Palatini scalar-tensor theories of gravity
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• Constraints on decaying early modified gravity from cosmological observations
• Sudden singularities in generalized hybrid metric-Palatini cosmologies
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• Black Hole Perturbations and Quasinormal Modes in Hybrid Metric-Palatini Gravity
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• Novel electrically charged wormhole, black hole and black bounce exact solutions in hybrid metric-Palatini gravity
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