Non-Gaussianities in Dissipative EFT of Inflation Coupled to a Fluid
  We studied models of inflation with a preferred clock specifying the end of
inflation and giving the curvature perturbations, coupled with another
non-equivalent clock that at late times defines the same frame and do not
contribute to the density perturbations. This can happen in the framework of
dissipative EFT of inflation where the additional degrees of freedom include a
fluid developing sound waves propagating with sound speed $c_{sr}$. The fluid
defines a preferred frame comoving with it. The paradigmatic example of this is
the warm inflation scenario. We studied the dynamics of this systems during
inflation and the three-point function. We saw that in the strong dissipation
regime the nonlinear parameter induced by the new terms is $|f_{\rm NL}| \sim
1/c_{sr}^2$, not enhanced by the dissipation parameter which enters the
two-point function. We checked that the squeezed limit of the three-point
function still satisfies the consistency condition with corrections of order
$\mathcal{O}(k_L^2/k_S^2)$. We computed the Planck constraints for the case of
warm inflation obtaining a bound of $\gamma\lesssim 10^5 H$ for the clock
coupled to radiation. For decreasing sound speed the bound decreases. We also
checked that the shape of the three-point function corresponding to the model
studied here is a mixture between equilateral and orthogonal with a small local
component, which is more consistent with Planck's results.
