Spontaneously breaking space-time: Poincare, gravity, cosmology and spinning objects

Abstract: Space-time symmetries are a crucial ingredient of any theoretical model in physics. Unlike internal symmetries, which may or may not be gauged and/or spontaneously broken, space-time symmetries do not admit any ambiguity: they are gauged by gravity, and any conceivable physical system (other than the vacuum) is bound to break at least some of them. Motivated by this observation, I will discuss how to couple gravity with the Goldstone fields that non-linearly realize spontaneously broken space-time symmetries by weakly gauging the Poincare symmetry group. I will discuss how this relates to effective field theories pertinent to cosmology such as “the effective field theory of inflation” and “solid inflation.” Furthermore, I will build a low energy effective action that describes spinning objects coupled to gravity.