Superluminality in the Bi- and Multi- Galileon
  We re-explore the Bi- and Multi-Galileon models with trivial asymptotic
conditions at infinity and show that propagation of superluminal fluctuations
is a common and unavoidable feature of these theories, unlike previously
claimed in the literature. We show that all Multi-Galileon theories containing
a Cubic Galileon term exhibit superluminalities at large distances from a point
source, and that even if the Cubic Galileon is not present one can always find
sensible matter distributions in which there are superluminal modes at large
distances. In the Bi-Galileon case we explicitly show that there are always
superluminal modes around a point source even if the Cubic Galileon is not
present. Finally, we briefly comment on the possibility of avoiding
superluminalities by modifying the asymptotic conditions at infinity.
