Late-time data require smaller sound horizon at recombination

TL;DR

This paper investigates whether modifications to the universe's expansion after recombination can resolve the Hubble constant discrepancy, finding that current models are disfavored and that new physics reducing the sound horizon at recombination are needed.

Contribution

The study compares phenomenological dark energy models with observational data, showing they cannot reconcile the Hubble tension without new physics reducing the sound horizon.

Findings

Phenomenological dark energy models fit supernova and galaxy survey data well.

These models are disfavored by the distance-redshift relation similar to LambdaCDM.

New physics reducing the sound horizon at recombination is suggested.

Abstract

The Hubble constant problem is that the values of Hubble constant from the observation of cosmic microwave background assuming the LambdaCDM model disagrees with the values from direct measurements. This problem suggests some new physics beyond the LambdaCDM model. Typically there are two ways of reconciliation: one is the realization of smaller value of sound horizon at recombination, and the other is the modification of the way of expansion of the universe after recombination. In this letter we examine the latter possibility by comparing two typical phenomenological dark energy models with the distance-redshift relation provided by Pantheon catalogue of supernova observations and galaxy surveys by BOSS and eBOSS collaborations. Though these phenomenological dark energy models globally fit observations better than the LambdaCDM model, they are strongly disfavored by the distance-redshift relation as almost the same level as the LambdaCDM model defined by cosmic microwave background observations. The distance-redshift relation strongly suggests some new physics which realize smaller value of sound horizon at recombination.