Interacting dark energy: The role of microscopic feedback in the dark sector

We investigate the impact on the classical dynamics of dark matter particles and dark energy of a nonminimal coupling in the dark sector, assuming that the mass of the dark matter particles is coupled to a dark energy scalar field. We show that standard results can be recovered only if the space-time variation of the dark energy scalar field is sufficiently smooth on the characteristic length scale of the dark matter particles, and we determine the associated constraint dependent on both the mass and radius of the dark matter particles and the coupling to the dark energy scalar field. We further show, using field theory numerical simulations, that a violation of such constraint results in a microscopic feedback effect strongly affecting the dynamics of dark matter particles, with a potential impact on structure formation and on the space-time evolution of the dark energy equation of state.

Figure 1

The top and middle panels show, respectively, the evolution of $f_{\text{DM}}^0$ and $f_{\text{DM}}^z$ (solid lines) and of $f_{\text{DE}}^0$ and $f_{\text{DE}}^z$ (dashed lines) considering $\xi =1.2$ for $\alpha =2$ (black and red lines) and $\alpha =0.2$ (blue and magenta lines). Note that the values of $f^0$ and $f^z$, represented by dotted lines in the top and middle panels, respectively, are always very close to unity as required by energy conservation. The lower panel shows the evolution of $r^U$ and $r^G$ for $\alpha =2$ (black and red lines, respectively) and $\alpha =0.2$ (blue and magenta lines, respectively).

Figure 2

Analogous to Fig. 1 for $\xi =0.8$.