Dark energy parametrization motivated by scalar field dynamics

Abstract

We propose a new dark energy (DE) parametrization motivated by the dynamics of a scalar field ϕ. We use an equation of state w parametrized in terms of two functions L and y, closely related to the dynamics of scalar fields, which is exact and has no approximation. By choosing an appropriate ansatz for L we obtain a wide class of behavior for the evolution of DE without the need to specify the scalar potential V. We parametrize L and y in terms of only four parameters, giving w a rich structure and allowing for a wide class of DE dynamics. Our w can either grow and later decrease, or it can happen the other way around; the steepness of the transition is not fixed and it contains the ansatz . Our parametrization follows closely the dynamics of a scalar field, and the function L allows us to connect it with the scalar potential . While the Universe is accelerating and the slow roll approximation is valid, we get . To determine the dynamics of DE we also calculate the background evolution and its perturbations, since they are important to discriminate between different DE models.