Running coupling: Does the coupling between dark energy and dark matter change sign during the cosmological evolution?

Understand

In this paper we put forward a running coupling scenario for describing the interaction between dark energy and dark matter.

• The dark sector interaction in our scenario is free of the assumption that the interaction term $Q$ is proportional to the Hubble expansion rate and the energy densities of dark sectors.
• We only use a time-variable coupling $b(a)$ (with $a$ the scale factor of the universe) to characterize the interaction $Q$.
• We propose a parametrization form for the running coupling $b(a)=b_0a+b_e(1-a)$ in which the early-time coupling is given by a constant $b_e$, while today the coupling is given by another constant, $b_0$.