DBI Galileons in the Einstein Frame: Local Gravity and Cosmology
  It is shown that a disformally coupled theory in which the gravitational
sector has the Einstein-Hilbert form is equivalent to a quartic DBI Galileon
Lagrangian, possessing non-linear higher derivative interactions, and hence
allowing for the Vainshtein effect. This Einstein Frame description
considerably simplifies the dynamical equations and highlights the role of the
different terms. The study of highly dense, non-relativistic environments
within this description unravels the existence of a disformal screening
mechanism, while the study of static vacuum configurations reveals the
existence of a Vainshtein radius, at which the asymptotic solution breaks down.
Disformal couplings to matter also allow the construction of Dark Energy
models, which behave differently than conformally coupled ones and introduce
new effects on the growth of Large Scale Structure over cosmological scales, on
which the scalar force is not screened. We consider a simple Disformally
Coupled Dark Matter model in detail, in which standard model particles follow
geodesics of the gravitational metric and only Dark Matter is affected by the
disformal scalar field. This particular model is not compatible with
observations in the linearly perturbed regime. Nonetheless, disformally coupled
theories offer enough freedom to construct realistic cosmological scenarios,
which can be distinguished from the standard model through characteristic
signatures.
