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 CMB, BAO, and SNIa 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 +0.96 −0.72 (68% CL). 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 +0.67 −0.86 km s −1 Mpc −1 when the prior is excluded. The TPM model improves χ 2 with respect to ΛCDM by ∆χ 2 = −23.72 with the H 0 prior and ∆χ 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 against the H 0 and σ8 tensions

“…See also [174]. 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 GN [115,116,175]. See also [176,177].…”

Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies

“…Other approaches considering varying gravitational constant are analysed in [907], that considering G N as a free parameter, and in [908] in the context of a cuscuta-galileon gravity theory. Finally, Ref [909] implements a sharp transition in the value of the effective gravitational constant prior recombination, effectively lowering the sound horizon at CMB last scattering and addressing both the H 0 and the S 8 tensions. Assessing the model against Planck 2018 TT,TE,EE + LowE and BAO data, the value inferred for the Hubble constant is H 0 = 69.22 +0.67 −0.86 km s −1 Mpc −1 [909].…”

Emergence of smooth distance and apparent magnitude in a lumpy Universe

“…There are also framedependent dark energy model approach [67] (this approach explains the SH0ES result but gives a large value of the Hubble constant from the BAO analysis). There is also proposals that explains the Hubble tension as a manifestation of the quantum measurement uncertainties [68], or the impact of the evolving gravitational constant leading to a modification of gravity at late-time [69][70][71]. All these approaches except the frame dependent dark energy(frame dependent dark energy model breaks 4D diffeomorphism invariance) assume that the FLRW background spacetime is valid on all scales and at all times.…”