Mild quasi-local non-Gaussianity as a signature of modified gravity   during inflation
  We show that modifications of Einstein gravity during inflation could leave potentially measurable imprints on cosmological observables in the form of non-Gaussian perturbations. This is due to the fact that these modifications appear in the form of an extra field that could have non-trivial interactions with the inflaton. We show it explicitly for the case $R+\alpha R^2$, where nearly scale-invariant non-Gaussianity at the level of $f_{\rm NL} \approx -(1$ to $30)$ can be obtained, in a quasi-local configuration. 
Nicola Bartolo, Dario Cannone, Raul Jimenez, Sabino Matarrese, Licia   Verde
astro-ph.CO hep-th