Natural inflation after Planck 2018

We calculate high-precision constraints on Natural Inflation relative to current observational constraints from Planck 2018 + BICEP/Keck(BK15) Polarization + BAO on r and nS, including post-inflationary history of the universe. We find that, for conventional post-inflationary dynamics, Natural Inflation with a cosine potential is disfavored at greater than 95% confidence out by current data. If we assume protracted reheating characterized by (w) over bar > 1/3, Natural Inflation can be brought into agreement with current observational constraints. However, bringing unmodified Natural Inflation into the 68% confidence region requires values of T-re below the scale of electroweak symmetry breaking. The addition of a SHOES prior on the Hubble Constant H-0 only worsens the fit.

Automated summary

The study found that under conventional post-inflationary dynamics, Natural Inflation with a cosine potential is disfavored by current data with a confidence level of over 95%. When considering prolonged reheating, Natural Inflation can be consistent with current observational constraints, but requires values of T-re below the scale of electroweak symmetry breaking. Adding a SHOES prior on the Hubble Constant H-0 only worsens the fit.