Johannes Noller (Oxford University)
Effective field theory (EFT) techniques, traditionally at home in particle physics, have recently been revolutionising the way we understand cosmology. In this talk I will discuss two examples of this: Firstly, I will show what consistent theories of gravitons we have discovered so far, highlighting how EFT techniques allow us to better understand the fundamental degrees of freedom of gravity and cosmology in the process. Secondly, I will demonstrate how to construct an exhaustive "effective" theory of linear cosmological perturbations - the regime most easily accessible to observational constraints in modern day cosmology. Along the way this will turn out to have something interesting to say about efficiently parametrised cosmologies (a la PPN or PPF) and the construction of fully fledged new cosmological theories.