The collision of high-energy particles in the early Universe can leave detectable correlations in the Cosmic Microwave Background and Large Scale Structure.

I will describe recent efforts to translate scattering theory from particle physics onto expanding spacetimes.

In particular, effective field theory techniques---used to search for new physics at colliders---can now be applied on a quasi-de Sitter background and establish new connections between cosmological observations and the fundamental physics that governs inflation.