No H_0 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.
