Kinetic screening of fields and stability of NEC violating configurations

Abstract

Following the discovery of the late-time acceleration, a multitude of extensions to General Relativity have been developed, seeking to shed light on this new phenomenon. Some of these models involve couplings to ordinary matter, suggesting an impact on gravitational effects. However, local measurements enforce severe constraints on these models, rendering them inadequate as cosmological theories. Thus there is purpose in finding mechanisms to hide the signature of these modifications in local environments, and as such restore the models viability. Screening mechanisms have been explored in the past, and successfully implemented in scalar field theories. In this thesis we will consider a screening mechanism inspired by k-mouflage on general vector field theories of the form $f(F^2)$ and $f(F^2, F\tilde{F})$. Further, we will analyse the stability about the screened solutions and look for healthy violations to the null energy condition.