Dynamics of dark energy with a coupling to dark matter
  Dark energy and dark matter are the dominant sources in the evolution of the late universe. They are currently only indirectly detected via their gravitational effects, and there could be a coupling between them without violating observational constraints. We investigate the background dynamics when dark energy is modelled as exponential quintessence, and is coupled to dark matter via simple models of energy exchange. We introduce a new form of dark sector coupling, which leads to a more complicated dynamical phase space and has a better physical motivation than previous mathematically similar couplings. 
Christian G. Boehmer, Gabriela Caldera-Cabral, Ruth Lazkoz, Roy   Maartens