Effective Field Theory Approach to Cosmological Initial Conditions: Self-Consistency Bounds and Non-Gaussianities

Effective Field Theory (EFT) is an efficient method for parametrizing unknown high energy physics effects on low energy data. When applied to time-dependent backgrounds, EFT must be supplemented with initial conditions. In these proceedings, I briefly describe such approach, especially in the case of inflationary, almost-de Sitter backgrounds. I present certain self-consistency constraints that bound the size of possible deviations of the initial state from the standard thermal vacuum. I also estimate the maximum size of non-Gaussianities due to a non-thermal initial state which is compatible with all bounds. These non-Gaussianities can be much larger than those due to nonlinearities in the action describing single-scalar slow roll inflation