Cosmological implications of the effective field theory of cosmic acceleration

We consider cosmological constraints arising from the background expansion history on the effective field theory of cosmic acceleration, a theoretical framework that allows for a unified way to classify both models of dark energy and modified gravity within the linear regime. In the Einstein frame, the most general action for the background can be written in terms of a canonical scalar field which is nonminimally coupled to matter. The leading corrections to the action are expressible through a quartic kinetic term, and scalar couplings to a Gauss-Bonnet curvature term and the Einstein tensor. We determine the implications of the terms in this general action for the predicted expansion history in the context of dynamical attractors. We find that each modifies the matter dominated and/or accelerative eras in ways that allow us to place cosmological constraints on them. We present current constraints on the effective action using the latest Type Ia supernovae, cosmic microwave background, and baryon acoustic oscillation data. This includes finding that the scalar field effective field theory with a coupled Gauss-Bonnet term and the data are significantly discrepant.