Very Hairy Inflation

TL;DR

This paper explores multi-stage monodromy inflation models with strong coupling corrections, showing they fit CMB data, produce detectable gravitational waves, and may be linked to resolving the H0 tension.

Contribution

It introduces a comprehensive analysis of monodromy inflation with strong coupling effects, including predictions for gravitational waves and non-Gaussianities, and discusses implications for cosmological tensions.

Findings

Flattened potentials with p ≤ 1/2 fit CMB data.

Produced relic gravitational waves with r between 0.006 and 0.035.

Generated equilateral non-Gaussianity close to observational bounds.

Abstract

We revisit the rollercoaster 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 $V \sim \phi^p + \ldots$ with $p \lesssim 1/2$, limited to $ N \lesssim 25 - 40$ efolds in the first stage of inflation, continue to fit the CMB. They yield $0.96 \lesssim n_s \lesssim 0.97$, and produce relic gravity waves with $0.006 \lesssim r \lesssim 0.035$, in full agreement with the most recent bounds from BICEP/{\it Keck}. The nonlinear derivative corrections generated by strong dynamics in EFT also lead to equilateral non-Gaussianity $f_{NL}^{eq} \simeq {\cal O}(1) - {\cal O}(10)$, close to the current observational bounds. Finally, in multi-stage rollercoaster, 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 Observatory, 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 may significantly alter the impact of BICEP/{\it Keck} data on models of inflation.