Toward inflation with ns=1 in light of the Hubble tension and implications for primordial gravitational waves

Recently, it has been found that complete resolution of the Hubble tension might point to a scale-invariant Harrison- Zeldovich spectrum of primordial scalar perturbation, i.e., n(s) = 1 for H-0 similar to 73 km/s/Mpc. We show that, for well-known slow- roll models, if inflation ends by a waterfall instability with respect to another field in the field space while inflaton is still at a deep slow-roll region, then ns can be lifted to n(s) = 1. A surprise of our result is that with prerecombination early dark energy, chaotic phi(2) inflation, strongly disfavored by Planck thorn BICEP/Keck in standard Lambda CDM, can be revived, which is now well within testable region of upcoming cosmic microwave background B-mode experiments.