The next non-Gaussianity frontier: what can a measurement with $\sigma(f_{\rm NL}) \lesssim 1$ tell us about multifield inflation?

Understand

Future galaxy surveys promise to probe local primordial non-Gaussianity at unprecedented precision, $\sigma(f_{\rm NL}) \lesssim 1$.

• We study the implications for multifield inflation by considering spectator models, where inflation is driven by the inflaton field, but the primordial perturbations are (partially) generated by a second, spectator field.
• We perform an MCMC likelihood analysis using Planck data to study quantitative predictions for $f_{\rm NL}$ and other observables for a range of such spectator models.
• We show that models where the primordial perturbations are dominated by the spectator field, while fine-tuned within the broader parameter space, typically predict $f_{\rm NL}$ of order unity.