Natural Metric-Affine Inflation

Understand

We consider here natural inflation in the low energy (two-derivative) metric-affine theory containing only the minimal degrees of freedom in the inflationary sector, i.e.

• the massless graviton and the pseudo-Nambu-Goldstone boson (PNGB).
• This theory contains the Ricci-like and parity-odd Holst invariants together with non-minimal couplings between the PNGB and the above-mentioned invariants.
• The Palatini and Einstein-Cartan realizations of natural inflation are particular cases of our construction.