Cosmology seminar: Massive Galileons and Vainshtein screening: a numerical perspective

Within the landscape of modified theories of gravity, progress in understanding the behaviour of, and developing tests for, screening mechanisms has been hindered by the complexity of the field equations involved, which are nonlinear in nature and characterised by a large hierarchy of scales. This is especially true of Vainshtein screening, where the fifth force is suppressed by high-order derivative terms becoming dominant within a large Vainshtein radius.

I will present \phi-enics, a numerical code based on the finite element method that can be used to overcome this problem, and apply it two case studies of interest for screening: a model containing high-order derivative operators in the equation of motion and one characterised by nonlinear self-interactions in two coupled scalar fields. I will use \phi-enics to perform a theoretical test of Vainshtein screening, by comparing the behaviour of a set of massive Galileon theories exhibiting screening with their UV completion. We show that the screening does not survive the extension, casting doubt over whether Vainshtein screening can take place within the limits of validity of the theories that invoke it.