Structure and evolution of Zel'dovich pancakes as probes of dark energy models

We examine how coupled dark matter and dark energy modify the development of Zel'dovich pancakes. We study how the various effects of these theories, such as a fifth force in the dark sector and a modified particle Hubble drag, produce variations in the redshifts of caustic formation and the present-day density profiles of pancakes. We compare our results in direct simulation to a perturbation theory approach for the dark energy scalar field. We determine the range of initial scalar field amplitudes for which perturbation theory is accurate in describing the development of the pancakes. Notably, we find that perturbative methods which neglect kinetic terms in the scalar field equation of motion are not valid for arbitrarily small perturbations. We also examine whether models that have been tuned to match the constraints of current observations can produce new observable effects in the nonlinear structure of pancakes. Our results suggest that a fully realistic three-dimensional simulation will produce significant new observable features, such as modifications to the mass function and halo radial density profile shapes, that can be used to distinguish these models from standard concordance cosmology and from each other.