Emergent Dark Energy from Dark Matter

We consider the cosmological dynamics of a scalar field in a potential with multiple troughs and peaks. We show that the dynamics of the scalar field will evolve from light dark matter-like behaviour (such as that of a light axion) to a combination of heavy dark matter-like and dark energy-like behaviour. We discuss the phenomenology of such a model, explaining how it can give rise to the cosmological constant, as well as how it can decouple the dark sector densities between the time of recombination and today, for both the homogeneous background and perturbations. The final form of the dark matter is axion-like, but with abundance and primordial isocurvature modes taking very different values from traditional, axionic, dark matter.