Early modified gravity in light of the $H_0$ tension and LSS data. (arXiv:2011.12934v1 [astro-ph.CO])

<a href="http://arxiv.org/find/astro-ph/1/au:+Braglia_M/0/1/0/all/0/1">Matteo Braglia</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ballardini_M/0/1/0/all/0/1">Mario Ballardini</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Finelli_F/0/1/0/all/0/1">Fabio Finelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koyama_K/0/1/0/all/0/1">Kazuya Koyama</a>

We present a model of Early Modified Gravity (EMG) consisting in a scalar

field $sigma$ with a non-minimal coupling to the Ricci curvature of the type

$M^2_{rm pl}+xi sigma^2$ plus a cosmological constant and a small effective

mass and demonstrate its ability to alleviate the $H_0$ tension while providing

a good fit to Cosmic Microwave Background (CMB) anisotropies and Baryon

Acoustic Oscillations (BAO) data. In this model the scalar field, frozen deep

in the radiation era, grows around the redshift of matter-radiation equality

because of the coupling to non-relativistic matter. The small effective mass,

which we consider here as induced by a quartic potential, then damps the scalar

field into coherent oscillations around its minimum at $sigma=0$, leading to a

weaker gravitational strength at early times and naturally recovering the

consistency with laboratory and Solar System tests of gravity. We analyze the

capability of EMG with positive $xi$ to fit current cosmological observations

and compare our results to the case without an effective mass and to the

popular early dark energy models with $xi=0$. We show that EMG with a quartic

coupling of the order of $lambdasimmathcal{O}({rm eV}^4/M_{rm pl}^4)$ can

substantially alleviate the $H_0$ tension also when the full shape of the

matter power spectrum is included in the fit in addition to CMB and Supernovae

(SN) data.

We present a model of Early Modified Gravity (EMG) consisting in a scalar

field $sigma$ with a non-minimal coupling to the Ricci curvature of the type

$M^2_{rm pl}+xi sigma^2$ plus a cosmological constant and a small effective

mass and demonstrate its ability to alleviate the $H_0$ tension while providing

a good fit to Cosmic Microwave Background (CMB) anisotropies and Baryon

Acoustic Oscillations (BAO) data. In this model the scalar field, frozen deep

in the radiation era, grows around the redshift of matter-radiation equality

because of the coupling to non-relativistic matter. The small effective mass,

which we consider here as induced by a quartic potential, then damps the scalar

field into coherent oscillations around its minimum at $sigma=0$, leading to a

weaker gravitational strength at early times and naturally recovering the

consistency with laboratory and Solar System tests of gravity. We analyze the

capability of EMG with positive $xi$ to fit current cosmological observations

and compare our results to the case without an effective mass and to the

popular early dark energy models with $xi=0$. We show that EMG with a quartic

coupling of the order of $lambdasimmathcal{O}({rm eV}^4/M_{rm pl}^4)$ can

substantially alleviate the $H_0$ tension also when the full shape of the

matter power spectrum is included in the fit in addition to CMB and Supernovae

(SN) data.

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