Discordances in Cosmology and the Violation of Slow-Roll Inflationary Dynamics

We identify examples of single field inflationary trajectories beyond the slow-roll regime that improve the fit to Planck 2018 data compared to a baseline Λ cold dark matter model with power law form of primordial spectrum and at the same time alleviate existing tensions between different datasets in the estimate of cosmological parameters such as H₀ and S₈. A damped oscillation in the first Hubble flow function-or equivalently a feature in the potential-and the corresponding localized oscillations in the primordial power spectrum partially mimic the improvement in the fit of Planck data due to A₋ or Ω₊. Compared to the baseline model, this model can lead simultaneously to a larger value of H₀ and a smaller value of S₈, a trend that can be enhanced when the most recent SH0ES measurement for H₀ is combined with Planck and BICEP-Keck 2018 data. Large scale structure data and more precise cosmic microwave background polarization measurements will further provide critical tests of this intermediate fast-roll phase.