No H_0 Assistance from Assisted Quintessence

TL;DR

This paper critically examines assisted quintessence as a solution to the Hubble tension, showing that its inherent features lead to conflicts with observational data and do not resolve the tension.

Contribution

It demonstrates that assisted quintessence cannot reconcile early dark energy models with current Hubble constant measurements, highlighting limitations of this approach.

Findings

Assisted quintessence predicts early dark energy that conflicts with Hubble data.

Scaling fields in the model undermine the concordance of Hubble constant measurements.

The scenario fails to resolve the Hubble tension due to inherent theoretical conflicts.

Abstract

Early dark energy, as a proposed solution to the Hubble tension, faces an additional "why now" problem. Why should dark energy emerge just prior to recombination, billions of years before the onset of cosmic acceleration? Assisted quintessence explains this connection by positing that multiple scaling fields build up over time to drive the present-day cosmic acceleration. In this framework, early dark energy is inevitable. Yet, we show that scaling also leads to the demise of the scenario: the same feature that solves the coincidence problem then spoils a concordance of the Hubble constant inferred from the cosmic microwave background with that from the local distance ladder. The failure of the model offers a novel lesson on the ability of new physics to resolve the Hubble tension.