Combined local and equilateral non-Gaussianities from multifield DBI
  inflation
  We study multifield aspects of Dirac-Born-Infeld (DBI) inflation. More
specifically, we consider an inflationary phase driven by the radial motion of
a D-brane in a conical throat and determine how the D-brane fluctuations in the
angular directions can be converted into curvature perturbations when the
tachyonic instability arises at the end of inflation. The simultaneous presence
of multiple fields and non-standard kinetic terms gives both local and
equilateral shapes for non-Gaussianities in the bispectrum. We also study the
trispectrum, pointing out that it acquires a particular momentum dependent
component whose amplitude is given by $f_{NL}^{loc} f_{NL}^{eq}$. We show that
this relation is valid in every multifield DBI model, in particular for any
brane trajectory, and thus constitutes an interesting observational signature
of such scenarios.
