No H0 assistance from assisted quintessence

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.

Automated summary

Early dark energy, proposed as a solution to the Hubble tension, faces a challenge regarding its emergence just before recombination. The model of assisted quintessence attempts to explain this connection through scaling fields, but ultimately leads to the failure of the scenario. This failure sheds light on the ability of new physics to resolve the Hubble tension.