Screening fifth forces in k-essence and DBI models
  New fifth forces have not yet been detected in the laboratory or in the solar
system, hence it is typically difficult to introduce new light scalar fields
that would mediate such forces. In recent years it has been shown that a number
of non-linear scalar field theories allow for a dynamical mechanism, such as
the Vainshtein and chameleon ones, that suppresses the strength of the scalar
fifth force in experimental environments. This is known as screening, however
it is unclear how common screening is within non-linear scalar field theories.
k-essence models are commonly studied examples of non-linear models, with DBI
as the best motivated example, and so we ask whether these non-linearities are
able to screen a scalar fifth force. We find that a Vainshtein-like screening
mechanism exists for such models although with limited applicability. For
instance, we cannot find a screening mechanism for DBI models. On the other
hand, we construct a large class of k-essence models which lead to the
acceleration of the Universe in the recent past for which the fifth force
mediated by the scalar can be screened.
