Testing Hu–Sawickif(R) gravity with the effective field theory approach

Abstract

We show how to fully map a specific model of modified gravity into the Einstein-Boltzmann solver EFTCAMB. This approach consists in few steps and allows to obtain the cosmological phenomenology of a model with minimal effort. We discuss all these steps, from the solution of the dynamical equations for the cosmological background of the model to the use of the mapping relations to cast the model into the effective field theory language and use the latter to solve for perturbations. We choose the Hu-Sawicki f (R) model of gravity as our working example. After solving the background and performing the mapping, we interface the algorithm with EFTCAMB and take advantage of the effective field theory framework to integrate the full dynamics of linear perturbations, returning all quantities needed to accurately compare the model with observations. We discuss some observational signatures of this model, focusing on the linear growth of cosmic structures. In particular we present the behavior of f σ 8 and E G that, unlike the ΛCDM scenario, are generally scale dependent in addition to redshift dependent. Finally, we study the observational implications of the model by comparing its cosmological predictions to the Planck 2015 data, including CMB lensing, the WiggleZ galaxy survey and the CFHTLenS weak lensing survey measurements. We find that while WiggleZ data favor a non-vanishing value of the Hu-Sawicki model parameter, log 10 (−f 0 R ), and consequently a large value of σ 8 , CFHTLenS drags the estimate of log 10 (−f 0 R ) back to the ΛCDM limit.

An extended action for the effective field theory of dark energy: a stability analysis and a complete guide to the mapping at the basis of EFTCAMB

“…The public version of EFTCAMB already contains the designer f (R) models [40,75,76], while the specific Hu-Sawicki model is currently being implemented through the full mapping procedure [77].…”

Do we have any hope of detecting scattering between dark energy and baryons through cosmology?

“…These have focused on the DE equation of state (EoS) w x and its time evolution, or on models of modified gravity that can account for DE, by studying imprints on the background evolution and on the late-time growth of structure (see e.g. Ishak et al 2006;Mena et al 2006;De Felice et al 2008;Giannantonio et al 2010;Lombriser et al 2012;Martinelli et al 2012;Hu et al 2016;Nunes et al 2017a,b;Renk et al 2017;Peirone et al 2018;Vagnozzi et al 2018;Du et al 2019;Yang et al 2019a), and finally on the propagation of astrophysical gravitational waves (see e.g. Creminelli & Vernizzi 2017;Sakstein & Jain 2017;Ezquiaga & Zumalacárregui 2017;Boran et al 2018;Baker et al 2017;Visinelli et al 2018;Crisostomi & Koyama 2018;Langlois et al 2018;Ezquiaga & Zumalacárregui 2018;.…”

On the stability conditions for theories of modified gravity in the presence of matter fields

“…The EFT approach provides a model independent framework to study linear order cosmological perturbations in theories of gravity which exhibit an additional scalar DoF, while at the same time it parametrizes in an efficient way existing models, since most of them can be directly mapped into this language [16,22,23,35,41]. Subsequently, the EFT approach has been implemented into the Einstein Boltzmann solver, CAMB/CosmoMC [42][43][44], creating EFTCAMB/EFTCosmoMC [19,20,[45][46][47][48] (http://www.eftcamb.org/), providing a perfect tool to test gravity models through comparison with observational data. EFTCAMB comes with a built-in module to explore the viability space of the underlying theory of gravity, which then can be used as priors.…”