The Importance of Slow-roll Corrections During Multi-field Inflation

TL;DR

This paper highlights the significance of slow-roll corrections in multi-field inflation models, showing they can be substantial and are crucial for precise cosmological predictions, especially during rapid field space changes.

Contribution

It demonstrates that next-to-leading order slow-roll corrections can be large in multi-field inflation, emphasizing their importance for accurate observational predictions.

Findings

Corrections can reach up to 20% in certain models.

Slow-roll corrections are significant during abrupt trajectory turns.

Implications for existing models to include these corrections for accuracy.

Abstract

We re-examine the importance of slow-roll corrections during the evolution of cosmological perturbations in models of multi-field inflation. We find that in many instances the presence of light degrees of freedom leads to situations in which next to leading order slow-roll corrections become significant. Examples where we expect such corrections to be crucial include models in which modes exit the Hubble radius while the inflationary trajectory undergoes an abrupt turn in field space, or during a phase transition. We illustrate this with two examples -- hybrid inflation and double quadratic inflation. Utilizing both analytic estimates and full numerical results, we find that corrections can be as large as 20%. Our results have implications for many existing models in the literature, as these corrections must be included to obtain accurate observational predictions -- particularly given the level of accuracy expected from CMB experiments such as Planck