What Planck does not tell us about inflation

Understand

Planck data has not found the 'smoking gun' of non-Gaussianity that would have necessitated consideration of inflationary models beyond the simplest canonical single field scenarios.

• This raises the important question of what these results do imply for more general models, and in particular, multi-field inflation.
• In this paper we revisit four ways in which two-field scenarios can behave differently from single field models; two-field slow-roll dynamics, curvaton-type behaviour, inflation ending on an inhomogeneous hypersurface and modulated reheating.
• We study the constraints that Planck data puts on these classes of behaviour, focusing on the latter two which have been least studied in the recent literature.