Fat Inflatons, Large Turns and the $\eta$-problem

Understand

It is commonly believed that a successful period of inflation driven by a single or several scalar fields requires a specific hierarchy of masses given by $M_{inf}\ll H \ll M_{heavy}$, where $M_{inf}$ can correspond to several or a single light field and $M_{heavy}\,\,\,$ corresponds to any heavy field that might be integrated out if it satisfies suitable conditions.

• This is at the heart of the so called $\eta$-problem in inflation, since large contributions to the masses of the inflatons might spoil the slow-roll conditions required for inflation.
• We show that, while this is an unavoidable conclusion in single field inflation, in multifield inflation, heavy fields as defined above, may be fully responsible for a successful period of what we call fat slow-roll inflation.
• Moreover we show that in this scenario, the turning rate of the inflationary trajectory, $\Omega/H$, is larger than one.