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Register a new userEarly modified gravity in light of the $H_0$ tension and LSS data
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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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We show that the $H_0$ tension can be resolved by making recombination earlier, keeping the fit to cosmic microwave background (CMB) data almost intact. We provide a suite of general necessary conditions to give a good fit to CMB data while realizing a high value of $H_0$ suggested by local measurements. As a concrete example for a successful scenario with early recombination, we demonstrate that a model with time-varying $m_e$ can indeed satisfy all the conditions. We further show that such a model can also be well fitted to low-$z$ distance measurements of baryon acoustic oscillation (BAO) and type-Ia supernovae (SNeIa) with a simple extension of the model. Time-varying $m_e$ in the framework of $Omega_kLambda$CDM is found to be a sufficient and excellent example as a solution to the $H_0$ tension, yielding $H_0=72.3_{-2.8} ^{+2.7},$km/sec/Mpc from the combination of CMB, BAO and SNeIa data even without incorporating any direct local $H_0$ measurements. Apart from the $H_0$ tension, this model is also favored from the viewpoint of the CMB lensing anomaly.
Although cosmic microwave background (CMB) is the most powerful cosmological probe of neutrino masses, it is in trouble with local direct measurements of $H_0$, which is called the $H_0$ tension. Since neutrino masses are correlated with $H_0$ in CMB, one can expect the cosmological bound on neutrino masses would be much affected by the $H_0$ tension. We investigate what impact this tension brings to cosmological bound on neutrino masses by assuming a model with modified recombination which has been shown to resolve the tension. We argue that constraints on neutrino masses become significantly weaker in models where the $H_0$ tension can be resolved.
We investigate the $H_0$ tension in a range of extended model frameworks beyond the standard $Lambda$CDM without the data from cosmic microwave background (CMB). Specifically, we adopt the data from baryon acoustic oscillation, big bang nucleosynthesis and type Ia supernovae as indirect measurements of $H_0$ to study the tension. We show that the estimated value of $H_0$ from indirect measurements is overall lower than that from direct local ones regardless of the data sets and a range of extended models to be analyzed, which indicates that, although the significance of the tension varies depending on models, the $H_0$ tension persists in a broad framework beyond the standard $Lambda$CDM model even without CMB data.
We investigate the recently introduced metastable dark energy (DE) models after the final Planck 2018 legacy release. The essence of the present work is to analyze their evolution at the level of perturbations. Our analyses show that both the metastable dark energy models considered in this article, are excellent candidates to alleviate the $H_0$ tension. In particular, for the present models, Planck 2018 alone can alleviate the $H_0$ tension within 68% CL. Along with the final cosmic microwave background data from the Planck 2018 legacy release, we also include external cosmological datasets in order to asses the robustness of our findings.
In this work, we obtain measurements of the Hubble constant in the context of modified gravity theories. We set up our theoretical framework by considering viable cosmological $f(R)$ and $f(T)$ models, and we analyzed them through the use of geometrical data sets obtained in a model-independent way, namely, gravitationally lensed quasars with measured time delays, standard clocks from cosmic chronometers, and standard candles from the Pantheon Supernovae Ia sample. We find $H_0=(72.4pm 1.4)$ km s$^{-1}$ Mpc$^{-1}$ and $H_0=(71.5pm 1.3)$ km s$^{-1}$ Mpc$^{-1}$ for the $f(R)$ and $f(T)$ models, respectively. Our results represent 1.9% and 1.8% measurements of the Hubble constant, which are fully consistent with the local estimate of $H_0$ by the Hubble Space Telescope. We do not find significant departures from general relativity, as our study shows that the characteristic parameters of the extensions of gravity beyond general relativity are compatible with the $Lambda$CDM cosmology. Moreover, within the standard cosmological framework, our full joint analysis suggests that it is possible to measure the dark energy equation of state parameter at 1.2% accuracy, although we find no statistical evidence for deviations from the cosmological constant case.
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