Effective Theory of Interacting Dark Energy

TL;DR

This paper develops a comprehensive framework for interacting dark energy and modified gravity, analyzing stability conditions, equations of motion, and illustrating with specific coupling scenarios, broadening previous models.

Contribution

It introduces a unifying formalism for dark energy and modified gravity with general matter couplings, extending prior coupled dark energy studies.

Findings

Derived conditions to avoid ghost and gradient instabilities.

Formulated equations of motion for background and perturbations.

Illustrated with scenarios involving nonminimally coupled dark matter or relativistic fluids.

Abstract

We present a unifying treatment of dark energy and modified gravity that allows distinct conformal-disformal couplings of matter species to the gravitational sector. In this very general approach, we derive the conditions to avoid ghost and gradient instabilities. We compute the equations of motion for background quantities and linear perturbations. We illustrate our formalism with two simple scenarios, where either cold dark matter or a relativistic fluid is nonminimally coupled. This extends previous studies of coupled dark energy to a much broader spectrum of gravitational theories.