General double monodromy inflation

Abstract

We revisit the roller-coaster cosmology based on multiple stages of monodromy inflation. Working within the framework of effective flux monodromy field theory, we include the full range of strong coupling corrections to the inflaton sector. We find that flattened potentials $V\ensuremath{\sim}{\ensuremath{\phi}}^{p}+\ensuremath{\cdots}$ with $p\ensuremath{\lesssim}1/2$, limited to $N\ensuremath{\lesssim}25\ensuremath{-}40$ $e$-folds in the first stage of inflation, continue to fit the cosmic microwave background. They yield $0.96\ensuremath{\lesssim}{n}_{s}\ensuremath{\lesssim}0.97$ and produce relic gravity waves with $0.006\ensuremath{\lesssim}r\ensuremath{\lesssim}0.035$, in full agreement with the most recent bounds from BICEP/Keck. The nonlinear derivative corrections generated by strong dynamics in effective field theory (EFT) also lead to equilateral non-Gaussianity ${f}_{\mathrm{NL}}^{\mathrm{eq}}\ensuremath{\simeq}\mathcal{O}(1)\ensuremath{-}\mathcal{O}(10)$, close to the current observational bounds. Finally, in the multistage roller coaster, an inflaton--hidden sector $U(1)$ coupling can produce a tachyonic chiral vector background, which converts rapidly into tensors during the short interruption by matter domination. The produced stochastic gravity waves are chiral, and so they may be clearly identifiable by gravity wave instruments like LISA, Big Bang Observer, Einstein Telescope, NANOgrav, or SKA, depending on the precise model realization. We also point out that the current attempts to resolve the ${H}_{0}$ tension using early dark energy generically raise ${n}_{s}$. This might significantly alter the impact of BICEP/Keck data on models of inflation.