Orthogonal non-Gaussianity in DBI Galileon: prospect for Planck
  polarisation and post-Planck experiments
  In this note, we study cosmic microwave background (CMB) constraints on
primordial non-Gaussianity in DBI galileon models in which an induced gravity
term is added to the Dirac-Born-Infeld (DBI) action. In this model, the
non-Gaussianity of orthogonal shape can be generated. We provide a relation
between theoretical parameters and orthogonal/equilateral non-linear parameters
using the Fisher matrix approach for the CMB bispectrum. In doing so, we
include the effect of the CMB transfer functions and experimental noise
properties by employing the recently developed \textsf{SONG} code. The relation
is also shown in the language of effective theory so that it can be applied to
general single-field models. Using the bispectrum Fisher matrix and the central
values for equilateral and orthogonal non-Gaussianities found by the Planck
temperature survey, we provide forecasts on the theoretical parameters of the
DBI galileon model. We consider the upcoming Planck polarisation data and the
proposed post-Planck experiments COrE and PRISM. We find that Planck
polarisation measurements may provide a hint for a non-canonical sound speed at
the 68% confidence level. COrE and PRISM will not only confirm a non-canonical
sound speed but also exclude the conventional DBI inflation model at more than
the 95% and 99% confidence level respectively, assuming that the central values
will not change. This indicates that improving constraints on non-Gaussianity
further by future CMB experiments is invaluable to constrain the physics of the
early universe.
