Tests of Standard Cosmology in Horava Gravity and Bayesian Evidence for a Closed Universe, and the Hubble Tension

TL;DR

This paper tests standard cosmology within Horava gravity, finding Bayesian evidence favoring a closed universe and reducing the Hubble tension, suggesting modifications to early universe physics could improve cosmic models.

Contribution

It provides Bayesian model comparison of Horava gravity-based cosmologies against standard LCDM, and shows observational preference for a closed universe and a lower Hubble constant.

Findings

Bayesian evidence strongly favors Horava gravity models over flat LCDM.

Data indicates a closed universe with specific curvature parameters.

Hubble tension is reduced in Horava gravity models.

Abstract

We consider some background tests of standard cosmology in the context of Horava gravity with different scaling dimensions for space and time, which has been proposed as a renormalizable, higher-derivative, Lorentz-violating quantum gravity model without ghost problems. We obtain the "very strong" and "strong" Bayesian evidence for our two cosmology models A and B, respectively, depending on the choice of parametrization based on Horava gravity, against the standard, spatially-flat, LCDM cosmology model based on general relativity. An MCMC analysis with observational data, including BAO, shows (a) preference of a closed universe with the curvature density parameter Omega_k=-0.005+- 0.0007, -0.004+0.003-0.001 and (b) reduction of the Hubble tension with the Hubble constant H_0=71.4+1.2-0.9, 69.5+1.6-0.9 km s^{-1} Mpc^{-1} for the models A, B. We comment on some possible further improvements for the "cosmic-tension problem" by considering more complete early universe physics, based on the Lorentz-violating standard model with anisotropic space-time scaling, consistently with Horava gravity, as well as the observational data which are properly adopted for the closed universe.