Inflation with $0 \leq c_{\rm s} \leq 1$
Abstract
We investigate a novel single field inflationary scenario which allows a transition between a slowroll kinflation with $c_{\rm s}$ of order unity and a ghost inflation with $c_{\rm s} \simeq 0$, where $c_{\rm s}$ is the sound speed for the curvature perturbations. We unify the two phases smoothly by appropriately taking into account a higher derivative scordatura term, which is always there from the effective field theory point of view but which becomes important only in the $c_{\rm s} \simeq 0$ regime. The model achieves the whole range of $0 \leq c_{\rm s} \leq 1$ avoiding strong coupling and gradient instability, and allows us to access the $c_{\rm s} \simeq 0$ regime in a selfconsistent manner. We also discuss implications to the formation of primordial black holes.
 Publication:

arXiv eprints
 Pub Date:
 October 2021
 arXiv:
 arXiv:2110.10731
 Bibcode:
 2021arXiv211010731G
 Keywords:

 High Energy Physics  Theory;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 26 pages, 5 figures