UV/IR relations in cosmology: unitarity and positivity of the EFT of inflation

by Tanguy Grall (University of Cambridge)



"Understanding the high-energy physics behind inflation and dark energy is one of the main goals of theoretical cosmology. In this talk I will show how to adapt tools from particle physics to study the high energy behaviour of cosmological theories. Because the background spacetime expansion spontaneously breaks Lorentz boosts symmetry, new techniques must be developed.

Focusing on curvature perturbations within the framework of the Effective Field Theory of inflation, first I will discuss how to probe the UV cut-off of the theory using new perturbative unitarity bounds. 

Then I will discuss how to adapt dispersion relation arguments from Lorentz invariant theories to theories with spontaneously broken Lorentz boosts. These so-called "positivity bounds" put constraints on the size and sign of coefficients in the low-energy EFT from the requirement that the UV completion is Lorentz invariant, unitary and causal. 

Finally I will discuss the implications of these results for primordial non-Gaussianities and contrast them with current bounds from Planck.“