Unraveling the effective fluid approach for f(R) models in the subhorizon approximation

Rubén Arjona, Wilmar Cardona, and Savvas Nesseris
Phys. Rev. D 99, 043516 – Published 12 February 2019

Abstract

We provide explicit formulas for the effective fluid approach of f(R) theories, such as the HuandSawicki and designer models. Using the latter and simple modifications to the class code, which we call EFCLASS, in conjunction with very accurate analytic approximations for the background evolution, we obtain competitive results in a much simpler and less error-prone approach. We also derive the initial conditions in matter domination, and we find they differ from those already found in the literature for a constant w model. A clear example is the designer model that behaves as ΛCDM in the background but has nonetheless dark energy perturbations. We then use the aforementioned models to derive constraints from the latest cosmological data, including supernovae, BAO, CMB, H(z) and growth-rate data, and find they are statistically consistent to the ΛCDM model. Finally, we show that the viscosity parameter cvis2 in realistic models is not constant as commonly assumed but rather evolves significantly over several orders of magnitude, something which could affect forecasts of upcoming surveys.

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  • Received 14 November 2018

DOI:https://doi.org/10.1103/PhysRevD.99.043516

© 2019 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Rubén Arjona*, Wilmar Cardona, and Savvas Nesseris

  • Instituto de Física Teórica UAM-CSIC, Universidad Autonóma de Madrid, Cantoblanco, 28049 Madrid, Spain

  • *ruben.arjona@estudiante.uam.es
  • wilmar.cardona@uam.es
  • savvas.nesseris@csic.es

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Issue

Vol. 99, Iss. 4 — 15 February 2019

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