D-BIonic Screening of Scalar Fields
  We study a new screening mechanism which is present in Dirac-Born-Infeld
(DBI)-like theories. A scalar field with a DBI-like Lagrangian is minimally
coupled to matter. In the vicinity of sufficiently dense sources,
non-linearities in the scalar dominate and result in an approximately constant
acceleration on a test particle, thereby suppressing the scalar force relative
to gravity. Unlike generic P(X) theories, screening happens within the regime
of validity of the effective field theory, thanks to the DBI symmetry. This
symmetry also allows the removal of a constant field gradient, like in
galileons. Not surprisingly, perturbations around the spherically-symmetry
background propagate superluminally, but we argue for a chronology protection
analogous to galileons. We derive constraints on the theory parameters from
tests of gravity and discuss various extensions.
