Reconciling early dark energy with a Harrison-Zeldovich spectrum

Understand

Recent attempts to fully resolve the Hubble tension from early dark energy models seem to favor a primordial Harrison-Zeldovich universe with its scalar spectrum being extremely scale invariant.

• Restoring the Harrison-Zeldovich spectrum within the single-field inflationary paradigm appears to be infeasible, turning to the multifield approach from either curvaton or waterfall models.
• In this Letter, we successfully align with the Harrison-Zeldovich spectrum within a single-field chaotic inflation by a nonminimal derivative coupling, and the previously disfavored chaotic potential by Planck+BICEP/Keck data in the standard $\Lambda$-cold-dark-matter model now returns back to the scope of future polarization observations of the cosmic microwave background.