I am a particle cosmologist, which means I apply the methods of theoretical particle physics to the outstanding problems in modern cosmology. Cosmology is the study of the origins, evolution, and fate of the Universe, and each of these is intimately bound up with the underlying fundamental laws of physics. I have been interested in the conceptual and observational implications of massive gravity and its generalization, massive bigravity, as well as more general field theoretical questions inspired by modifying general relativity, and questions of effective field theories.