Bogoliubov Excited States and the Lyth Bound
  We show that Bogoliubov excited scalar and tensor modes do not alleviate Planckian evolution during inflation if one assumes that $r$ and the Bogoliubov coefficients are approximately scale invariant. We constrain the excitation parameter for the scalar fluctuations, $\beta$, and tensor perturbations, $\tilde{\beta}$, by requiring that there be at least three decades of scale invariance in the scalar and tensor power spectrum. For the scalar fluctuations this is motivated by the observed nearly scale invariant scalar power spectrum. For the tensor fluctuations this assumption may be shown to be valid or invalid by future experiments. 
Aditya Aravind, Dustin Lorshbough, Sonia Paban
astro-ph.CO gr-qc hep-ph hep-th