Toward a simultaneous resolution of the $H_0$ and $S_8$ tensions: early dark energy and an interacting dark sector model

TL;DR

This paper explores a combined early dark energy and interacting dark sector model to address both the Hubble constant and $S_8$ tensions, finding modest improvements but no full resolution.

Contribution

It introduces a mixed model of EDE and dark sector interaction and evaluates its effectiveness in simultaneously alleviating both cosmological tensions.

Findings

The mixed model modestly reduces both $H_0$ and $S_8$ tensions.

Dark sector interaction suppresses structure growth and lowers $S_8$.

EDE increases $H_0$ but less effectively when combined with dark sector interaction.

Abstract

The tension between the Hubble constant ($H_0$) inferred from the cosmic microwave background (CMB) and that measured from late-time observations, such as the local distance ladder, is a major challenge in modern cosmology. Early dark energy (EDE) has been proposed as a possible resolution to the $H_0$ tension, but it typically worsens the $S_8$ tension by enhancing the small-scale matter power spectrum due to an increased cold dark matter density. To address this issue, we propose a model that combines EDE with an interacting dark energy-dark matter (iDEDM) scenario, and investigate whether this mixed model can simultaneously resolve both tensions. We find that the DE-DM interaction suppress the growth of structure and reduce $S_8$, while EDE contributes to increase $H_0$, although less effectively than in the EDE-only case. Our MCMC analysis using Planck 2018, DESI BAO, DES, Pantheon+, and SH0ES data shows that the mixed model provides modest improvements in both tensions, although it does not fully resolve either. This limitation appears to stem from the fact that both EDE and iDEDM independently favor a higher present-day matter density, which reduces the angular diameter distance and limits the degree to which EDE can lower the sound horizon.