Bimetric structure formation: non-Gaussian predictions
  The minimal bimetric theory employing a disformal transformation between
matter and gravity metrics is known to produce exactly scale-invariant
fluctuations. It has a purely equilateral non-Gaussian signal, with an
amplitude smaller than that of DBI inflation (with opposite sign) but larger
than standard inflation. We consider non-minimal bimetric models, where the
coupling $B$ appearing in the disformal transformation ${\hat g}_{\mn}= g_{\mn}
-B\partial_\mu\phi\partial_\nu\phi$ can run with $\phi$. For power-law
$B(\phi)$ these models predict tilted spectra. For each value of the spectral
index, a distinctive distortion to the equilateral property can be found. The
constraint between this distortion and the spectral index can be seen as a
"consistency relation" for non-minimal bimetric models.
