Strong seminar: Nils Albin Nilsson

Speaker: Nils Albin Nilsson (IBS Center for Theoretical Physics of the Universe, Korea)

Title: Gravitational waves and vacuum solutions with spacetime-symmetry breaking

Abstract: Spacetime-symmetry breaking in the gravity sector can be tightly constrained using gravitational waves, e.g. through propagation speed and polarisation content. In this talk, I will review some recent results in gravitational symmetry breaking using EFT. Starting with explicit diffeomorphism violation, I will show that it is possible to circumvent a subset of the severe no-go constraints in the linearised-gravity limit. Nonetheless, I will show that more no-go issues can be identified even in linearised gravity, including the existence of an unsuppressed polarisation of gravitational waves, in contrast to the case of spontaneous breaking, where I will show that five polarisations appear. I will also review the possibility of obtaining exact solutions (black holes, horizon solutions) in EFT with explicit breaking, which exhibit interesting phenomenology and can be used to obtain further constraints.