Cosmological dynamics with non-linear interactions

TL;DR

This paper explores non-linear interactions between dark matter and dark energy, revealing diverse final states of the universe, including stable ratios and oscillations, with some models fitting supernova data and addressing the coincidence problem.

Contribution

It introduces a class of non-linear dark sector interactions and analyzes their cosmological implications, including stable and oscillatory solutions, extending beyond standard models.

Findings

Final states can differ from LCDM, with stable or oscillating dark matter-dark energy ratios.

A specific analytic solution fits supernova data well.

Dynamical analysis identifies stationary points relevant to the coincidence problem.

Abstract

We consider a set of non-linear interactions between dark matter and dark energy which comprises couplings proportional to products of (powers of) the energy densities of both dark components and of the total energy. We demonstrate that under such conditions the final state of the Universe may differ substantially from that of the standard LCDM model. In particular, the ratio of the energy densities of dark matter and dark energy may approach a stable finite value or oscillate about such a value. Stationary solutions of this type require a phantom-type "bare" equation of state of the dark energy which, however, does not lead to a big-rip singularity. A corresponding analytic solution for a particular case is shown to be consistent with the supernova type Ia (SNIa) data from the Union2 set. For a broader class of interactions, a dynamical system analysis classifies stationary points with emphasis on their potential relevance for the coincidence problem.