Avoiding the string swampland in single-field inflation: excited initial states

Abstract

One class of single-field inflationary models compatible with the recently-conjectured Swampland criteria would be those in which a Hubble slow-roll arameter ϵH is not the same as ϵV ∼ (V′/V)2. However, a roadblock for these models (with a convex potential) lie in the unacceptably high tensor-to-scalar ratio, r, generically predicted by them. In this work, illustrating through an explicit example, we point out that having a non-Bunch-Davies component to the initial state of cosmological perturbations makes the value of r compatible with observations. In this way, we lay down a new path even for standard models of slow-roll inflation to be consistent with the Swampland criteria by invoking deviations from the Bunch-Davies initial state.