Can Conformally Invariant Modified Gravity Solve The Hubble Tension?. (arXiv:2011.13853v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Abadi_T/0/1/0/all/0/1">Tal Abadi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kovetz_E/0/1/0/all/0/1">Ely D. Kovetz</a>
The discrepancy between early-Universe and direct measurements of the Hubble
constant, known as the Hubble tension, recently became a pressing subject in
high precision cosmology. As a result, a large variety of theoretical models
have been proposed to relieve this tension. In this work we analyze a
conformally-invariant modified gravity (CIMG) model of an evolving
gravitational constant due to the coupling of a scalar field to the Ricci
scalar, which is theoretically advantageous as it has only one free parameter
and its influence is concentrated around matter-radiation equality, as required
for solutions to the Hubble tension based on increasing the sound horizon at
recombination. Inspired by similar recent analyses of so-called
early-dark-energy models, we constrain the CIMG model using a combination of
early and late-Universe cosmological datasets. In addition to the Planck 2018
cosmic microwave background (CMB) anisotropies and weak lensing measurements,
baryon acoustic oscillations and the Supernova H0 for the Equation of State
datasets, we also use large-scale structure (LSS) datasets such as the Dark
Energy Survey year 1 and the full-shape power spectrum likelihood from the
Baryon Oscillation Spectroscopic Survey, including its recent analysis using
effective field theory, to check the effect of the CIMG model on the (milder)
S8 tension between the CMB and LSS. We find that the CIMG model can slightly
relax the Hubble tension, with H0 = 69.6 +- 1.6 km/s/Mpc at 95% CL, while
barely affecting the S8 tension. However, current data does not exhibit strong
preference for CIMG over the standard cosmological model. Lastly, we show that
the planned CMB-S4 experiment will have the sensitivity required to distinguish
between the CIMG model and the more general class of models involving an
evolving gravitational constant.
The discrepancy between early-Universe and direct measurements of the Hubble
constant, known as the Hubble tension, recently became a pressing subject in
high precision cosmology. As a result, a large variety of theoretical models
have been proposed to relieve this tension. In this work we analyze a
conformally-invariant modified gravity (CIMG) model of an evolving
gravitational constant due to the coupling of a scalar field to the Ricci
scalar, which is theoretically advantageous as it has only one free parameter
and its influence is concentrated around matter-radiation equality, as required
for solutions to the Hubble tension based on increasing the sound horizon at
recombination. Inspired by similar recent analyses of so-called
early-dark-energy models, we constrain the CIMG model using a combination of
early and late-Universe cosmological datasets. In addition to the Planck 2018
cosmic microwave background (CMB) anisotropies and weak lensing measurements,
baryon acoustic oscillations and the Supernova H0 for the Equation of State
datasets, we also use large-scale structure (LSS) datasets such as the Dark
Energy Survey year 1 and the full-shape power spectrum likelihood from the
Baryon Oscillation Spectroscopic Survey, including its recent analysis using
effective field theory, to check the effect of the CIMG model on the (milder)
S8 tension between the CMB and LSS. We find that the CIMG model can slightly
relax the Hubble tension, with H0 = 69.6 +- 1.6 km/s/Mpc at 95% CL, while
barely affecting the S8 tension. However, current data does not exhibit strong
preference for CIMG over the standard cosmological model. Lastly, we show that
the planned CMB-S4 experiment will have the sensitivity required to distinguish
between the CIMG model and the more general class of models involving an
evolving gravitational constant.
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