Non-Gaussianity After BICEP2

We analyze primordial non-Gaussianity in single-field inflationary models when the tensor-to-scalar ratio is large. Our results show that detectable levels of non-Gaussianity $f_{NL}\sim 50$ are still possible in the simplest class of models described by the effective theory of inflation. However, the shape is very tightly constrained, making a sharp prediction that could be confirmed or falsified by a future detection of non-Gaussianity.

Figure 1

Shape of the bispectrum induced by ${\dot{\pi }}^3$. As usual, we show $B(1,r_2^2,r_3^2)r_2^2{r}_3^2$, where $r_i=k_i/k_1$ and we normalize to 1 in the equilateral limit.

Figure 2

Constraints on $f_{NL}$ in the next-to-minimal model of inflation (10) for large $r$ (12) for the equilateral versus orthogonal plane, assuming $c_s>0.1$ (narrow black strip) or $c_s>0.05$ (wider red strip), with the 1-and $2\sigma$ Planck constraints superimposed (circular blue regions).