The Cosmological Constant Potential: a resolution to the Hubble tension via the cosmological sound horizon

TL;DR

This paper proposes a scalar field model with a variable potential that modifies the early universe's sound horizon, effectively resolving the Hubble tension without introducing new physics after photon decoupling.

Contribution

It introduces a novel scalar field potential framework that alters the early universe dynamics to reconcile local and cosmological measurements of the Hubble constant.

Findings

The model reduces the cosmological sound horizon at high redshift.

It fully alleviates the Hubble tension when tested with CMB, BAO, and $H_0$ datasets.

No new physics is required after photon decoupling.

Abstract

The cosmological constant term can be seen as a constant potential for a (scalar) field. In this viewpoint, at late times, the field is stopped rolling and behaves as a cosmological constant ($w=-1$). While at the early universe, its kinetic term can be dominant and behaves as a stiff fluid ($w=+1$). This new phase lowers the cosmological sound horizon by increasing the Hubble parameter for very high redshifts. Consequently, the lower cosmological sound horizon results in the higher Hubble constant at the present time. This early phase ends before the photon decoupling, so we do not expect any new physics after the last scattering surface. We checked this model in the presence of (reduced) CMB, BAO's and $H_0$ datasets and could show the Hubble tension is fully relieved.