Modified gravity versus shear viscosity: Imprints on the scalar matter perturbations

@article{Barbosa2018ModifiedGV,
  title={Modified gravity versus shear viscosity: Imprints on the scalar matter perturbations},
  author={Camila S. Barbosa and Hermano Velten and J'ulio C'esar Fabris and Rudnei O. Ramos},
  journal={Physical Review D},
  year={2018}
}
Cosmological scalar perturbation theory studied in the Newtonian gauge depends on two potentials $\Phi$ and $\Psi$. In General Relativity (GR) they must coincide ($\Phi=\Psi$) in the absence of anisotropic stresses sourced by the energy momentum tensor. On the other hand, it is widely accepted in the literature that potential deviations from GR can be parameterized by $\Phi\neq \Psi$. The latter feature is therefore present in both GR cosmologies equipped with shear viscous fluids or modified… 
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