Cosmological evolution of quintessence with a sign-changing interaction   in dark sector
  By analysing the cosmological dynamical system with a dark-sector interaction which changes sign during the cosmological evolution, we find a scaling attractor to help to alleviate the cosmic-coincidence problem. This result shows that this interaction can bring new features to the cosmology. 
Ming Zhang, Cheng-Yi Sun, Zhan-Ying Yang, Rui-Hong Yue
hep-th gr-qc