Pedro Gregorio Carrilho (Queen Mary University of London, United Kingdom)
We derive the evolution equation for the second order part of the curvature perturbation using standard techniques of cosmological perturbation theory. The result is valid at all scales and includes all contributions from vector and tensor perturbations, as well as anisotropic stress. We write all our results purely in terms of gauge invariant quantities, so as to facilitate future work in any choice of gauge. Taking the large-scale approximation, we find that a conserved quantity exists only if, in addition to the non-adiabatic pressure, the transverse traceless part of the anisotropic stress tensor is also negligible.