The effective field theory of multifield ination

Abstract

We generalize the Effective Field Theory of Ination to include additional light scalar degrees of freedom that are in their vacuum at the time the modes of interest are crossing the horizon. In order to make the scalars light in a natural way we consider the case where they are the Goldstone bosons of a global symmetry group or are partially protected by an approximate supersymmetry. We write the most general Lagrangian that couples the scalar mode associated to the breaking of time translation during ination to the additional light scalar fields. This Lagrangian is constrained by diffeomorphism invariance and the additional symmetries that keep the new scalars light. This Lagrangian describes the uctuations around the time of horizon crossing and it is supplemented with ageneral parameterization describing how the additional uctuating fields can affect cosmological perturbations. We find that multifield ination can reproduce the non-Gaussianities that can be generated in single field ination but can also give rise to new kinds of non- Gaussianities. We find several new three-point function shapes. We show that in multifield ination it is possible to naturally suppress the three-point function making the four-point function the leading source of detectable non-Gaussianities. We find that under certain circumstances, i.e. if specific shapes of non-Gaussianities are detected in the data, one could distinguish between single and multifield ination and sometimes even among the variousmechanisms that kept the additional fields light. © 2012 SISSA.