Generalized dark energy interactions with multiple fluids
  In the search for an explanation for the current acceleration of the Universe, scalar fields are the most simple and useful tools to build models of dark energy. This field, however, must in principle couple with the rest of the world and not necessarily in the same way to different particles or fluids. We provide the most complete dynamical system analysis to date, consisting of a canonical scalar field conformally and disformally coupled to both dust and radiation. We perform a detailed study of the existence and stability conditions of the systems and comment on constraints imposed on the disformal coupling from Big-Bang Nucleosynthesis and given current limits on the variation of the fine-structure constant. 
Carsten van de Bruck, Jurgen Mifsud, Jos\'e P. Mimoso, Nelson J. Nunes
gr-qc astro-ph.CO hep-th