Cosmological constraints with the Effective Fluid approach for Modified Gravity. (arXiv:2012.05282v2 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Cardona_W/0/1/0/all/0/1">Wilmar Cardona</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Arjona_R/0/1/0/all/0/1">Rubén Arjona</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Estrada_A/0/1/0/all/0/1">Alejandro Estrada</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nesseris_S/0/1/0/all/0/1">Savvas Nesseris</a>
Cosmological constraints of Modified Gravity (MG) models are seldom carried
out rigorously. First, even though general MG models evolve differently (i.e.,
background and perturbations) to the standard cosmological model, it is usual
to assume a $Lambda$CDM background. This treatment is not correct and in the
era of precision cosmology could induce undesired biases in cosmological
parameters. Second, neutrino mass is usually held fixed in the analyses which
could obscure its relation to MG parameters. In a couple of previous papers we
showed that by using the Effective Fluid Approach we can accurately compute
observables in fairly general MG models. An appealing advantage of our approach
is that it allows a pretty easy implementation of this kinds of models in
Boltzmann solvers (i.e., less error–prone) while having a useful analytical
description of the effective fluid to understand the underlying physics. This
paper illustrates how an effective fluid approach can be used to carry out
proper analyses of cosmological constraints in MG models. We investigated three
MG models including the sum of neutrino masses as a varying parameter in our
Markov Chain Monte Carlo analyses. Two models (i.e., Designer $f(R)$ [DES-fR]
and Designer Horndeski [HDES]) have a background matching $Lambda$CDM, while
in a third model (i.e., Hu $&$ Sawicki $f(R)$ model [HS]) the background
differs from the standard model. In this way we estimate how relevant the
background is when constraining MG parameters along with neutrinos’ masses. We
implement the models in the popular Boltzmann solver CLASS and use recent,
available data (i.e., Planck 2018, CMB lensing, BAO, SNIa Pantheon compilation,
$H_0$ from SHOES, and RSD Gold-18 compilation) to compute tight cosmological
constraints in the MG parameters that account for deviation from the
$Lambda$CDM model. [abridged]
Cosmological constraints of Modified Gravity (MG) models are seldom carried
out rigorously. First, even though general MG models evolve differently (i.e.,
background and perturbations) to the standard cosmological model, it is usual
to assume a $Lambda$CDM background. This treatment is not correct and in the
era of precision cosmology could induce undesired biases in cosmological
parameters. Second, neutrino mass is usually held fixed in the analyses which
could obscure its relation to MG parameters. In a couple of previous papers we
showed that by using the Effective Fluid Approach we can accurately compute
observables in fairly general MG models. An appealing advantage of our approach
is that it allows a pretty easy implementation of this kinds of models in
Boltzmann solvers (i.e., less error–prone) while having a useful analytical
description of the effective fluid to understand the underlying physics. This
paper illustrates how an effective fluid approach can be used to carry out
proper analyses of cosmological constraints in MG models. We investigated three
MG models including the sum of neutrino masses as a varying parameter in our
Markov Chain Monte Carlo analyses. Two models (i.e., Designer $f(R)$ [DES-fR]
and Designer Horndeski [HDES]) have a background matching $Lambda$CDM, while
in a third model (i.e., Hu $&$ Sawicki $f(R)$ model [HS]) the background
differs from the standard model. In this way we estimate how relevant the
background is when constraining MG parameters along with neutrinos’ masses. We
implement the models in the popular Boltzmann solver CLASS and use recent,
available data (i.e., Planck 2018, CMB lensing, BAO, SNIa Pantheon compilation,
$H_0$ from SHOES, and RSD Gold-18 compilation) to compute tight cosmological
constraints in the MG parameters that account for deviation from the
$Lambda$CDM model. [abridged]
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