An Exploration of an Early Gravity Transition in Light of Cosmological Tensions

Abstract

We study a step-like transition in the value of the effective Planck mass (or effective gravitational constant) on cosmological scales prior to recombination. We employ cosmic microwave background, baryon acoustic oscillations, and Type Ia supernova data and find they are sufficient to strongly constrain our implementation of the effective field theory of dark energy and modified gravity, used to model the transition, to a limited parameter space. The data prefer a ∼5% shift in the value of the effective Planck mass (<10% at 2σ) prior to recombination. This Transitional Planck Mass (TPM) model is free to undergo its transition at any point over multiple decades of scale factor prior to recombination, log 10 ( a ) = − 5.32 − 0.72 + 0.96 (68% confidence level). This lowers the sound horizon at last scattering, which increases the Hubble constant to 71.09 ± 0.75 km s−1 Mpc−1 with a combination of local measurements as prior and to 69.22 − 0.86 + 0.67 km s−1 Mpc−1 when the prior is excluded. The TPM model improves χ 2 with respect to ΛCDM by Δχ 2 = −23.72 with the H 0 prior and Δχ 2 = −4.8 without the prior. The model allows for both H 0 > 70 kms−1 Mpc−1 and S 8 < 0.80 simultaneously with lower values of S 8 due to a reduction in the matter density Ω m to offset the increase in H 0 relative to ΛCDM. While this is a particular modified gravity model, studying other variants of modified gravity may be a productive path for potentially resolving cosmological tensions while avoiding the need for a cosmological constant.

Running Vacuum in the Universe: Phenomenological Status in Light of the Latest Observations, and Its Impact on the σ8 and H0 Tensions

“…However, these measurements still have large uncertainties and cannot arbitrate the Hubble tension yet; see also [179]. 15 A similar phenomenology is found in the context of some modified gravity theories with a mild time evolution of G and a non-negligible shift of its value with respect to G N [118,119,180]. See also [181,182].…”

Cosmic chronometers to calibrate the ladders and measure the curvature of the Universe. A model-independent study

“…Apart from that, it is also interesting to perform these calibrations in a model-independent way. Many models have been proposed in the last years to alleviate the H0 tension: coupled dark energy models (Pettorino 2013;Gómez-Valent et al 2020;Agrawal et al 2021;Archidiacono et al 2022;Goh et al 2022), modified gravity (Solà Peracaula et al 2019Ballesteros et al 2020;Braglia et al 2020Braglia et al , 2021Benevento et al 2020Benevento et al , 2022, running vacuum models (Solà Peracaula et al 2021), early dark energy (Poulin 1 The Planck collaboration has measured the CMB acoustic angular scale to 0.03% precision, 100θ * = 1.04110 ± 0.00031 (Aghanim et al 2020). Niedermann & Sloth 2021;Agrawal et al 2019;Hill et al 2020;Gómez-Valent et al 2021, scenarios with varying atomic constants (Liu et al 2020a;Sekiguchi & Takahashi 2021;Lee et al 2022), or models with primordial magnetic fields (Jedamzik & Pogosian 2020).…”

Stringy running vacuum model and current tensions in cosmology

“…This is aligned with previous results in the literature found in the context of Brans-Dicke with a cosmological constant [87,128] and the type-II RRVM [40,41], which exhibit a similar preference for larger values of G when the SH0ES information is considered on top of CMB, background and LSS data in the fitting analyses. See also [129]. This clear departure of the value of G preferred at cosmological scales from the one measured locally can be thought of as natural in the context of models with a space-time dependent gravitational coupling, but it requires a physical mechanism that explains the transition between the cosmological and astrophysical regimes, see e.g.…”