Collection Number C15019
Description Superluminality in Effective Field Theories for Cosmology
Collection Type Conference/School

Causal structures in Massive gravity and Gauss-Bonnet gravity

Abstract In General Relativity, gravitons propagate to null directions, because of its well-organized structures. Modifying the gravity theory slightly, meanwhile, the beautiful structure is broken and gravitons can easily propagate superluminaly. Here, applying the characteristic method, which is the well-established powerful way to analyze causal structures, the causal structures in Massive gravity and Gauss-Bonnet gravity are analyzed. We discuss the superluminality, acausality and black holes.

Causality constraints and the lightcone

Abstract It is an attractive idea that effective theories admitting a consistent UV completion require quanta to propagate sub-luminally in non-trivial backgrounds. However, there is a counter example to this proposition in the form of QED in a curved geometry, a theory that is certainly causal. Nevertheless, Drummond and Hathrell showed that there is always at least one choice of polarization for which low frequency photons propagate super-luminally.

Subluminal Vainshtein Screening in Massive Gravity

Abstract I will discuss the Vainshtein mechanism in massive gravity. I will show that the spherically symmetric backgrounds that were believed to have superluminal sound speed are in fact unstable. Instead, there is a new class of phenomenologically relevant solutions with stable and subluminal perturbations.

Lessons from QuantumLand

Abstract Theories with large kinetic interactions have very relevant phenomenological applications in cosmology, in particular in the context of cosmic acceleration. Their Effective Field Theory (EFT) description relies on the so-called Vainshtein effect being operative. When incorporated at the quantum level, this mechanism ensures the validity of the theory in a non-trivial way. I will discuss how to estimate the regime of validity of such EFTs on the basis of computing the quantum corrections to the classical theory.