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 parameter ${\epsilon }_{\text{H}}$ is not the same as ${\epsilon }_{\text{V}}\sim (V^{\prime }/V{)}^2$. 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.

9 pages; comments welcome; v2: version accepted in JHEP