Cosmology with interaction in the dark sector

Unless some unknown symmetry in nature prevents or suppresses a nonminimal coupling in the dark sector, the dark energy field may interact with the pressureless component of dark matter. In this paper, we investigate some cosmological consequences of a general model of interacting dark matter-dark energy characterized by a dimensionless parameter $ϵ$. We derive a coupled scalar field version for this general class of scenarios and carry out a joint statistical analysis involving type Ia supernovae data (Legacy and Constitution sets), measurements of baryon acoustic oscillation peaks at $z=0.20$ (2dFGRS) and $z=0.35$ (SDSS), and measurements of the Hubble evolution $\mathrm{H}(z)$. For the specific case of vacuum decay ($w=-1$), we find that, although physically forbidden, a transfer of energy from dark matter to dark energy is favored by the data.

Figure 1

Left panel: The ratio ${\rho }_{\mathrm{de}}/{\rho }_{\mathrm{dm}}$ as a function of the redshift parameter $z$ [Eqs. (1, 2)] for some selected values of $ϵ$ and $w$ and ${\Omega }_{\mathrm{de},0}/{\Omega }_{\mathrm{dm},0}\simeq 3$. Note that, for large and positive values of $ϵ$, the relative contribution of dark energy to dark matter may be significant at early times. Right panel: The potential $U(\Phi )$ [Eqs. (6, 7, 8)] as a function of the field for some selected values of $w$ and $ϵ=0.1$ and ${\Omega }_{\mathrm{dm}}=0.23$. In this panel, “NB” means that the baryons participate in the interacting process, whereas “WB” means that they were regarded as a separately conserved component contributing with ${\Omega }_{b,0}=0.0416$.

Figure 2

Contours of ${\chi }^2$ in the planes $w-ϵ$ (left panel), ${\Omega }_{\mathrm{dm},0}-ϵ$ (middle panel), and ${\Omega }_{\mathrm{dm},0}-ϵ$ with $w=-1$ (right panel). These contours are drawn for $\Delta {\chi }^2=2.30$ and 6.17. In all panels, dashed lines correspond to the joint analysis involving $\mathrm{SNLS}+\mathrm{BAO}+\mathrm{H}(z)$ measurements whereas the solid ones correspond to $\mathrm{CS}+\mathrm{BAO}+\mathrm{H}(z)$ data. The shadowed area in the right panel stands for the thermodynamical constraint on $ϵ$ discussed in Ref. 8.