MULTIFIELD COSMOLOGICAL PERTURBATIONS AT THIRD ORDER AND THE EKPYROTIC TRISPECTRUM

We explain the motivation and main results of our work in Ref. 1. Using the covariant formalism, we derive the equations of motion for adiabatic and entropy perturbations at third order in perturbation theory for cosmological models involving two scalar fields, and use these equations to calculate the trispectrum of ekpyrotic and cyclic models. The non-linearity parameters f_NL and g_NL are found to combine to leave a very distinct observational imprint.