Can dark matter decay in dark energy?

We analyze the interaction between dark energy and dark matter from a thermodynamical perspective. By assuming they have different temperatures, we study the possibility of occurring a decay from dark matter into dark energy, characterized by a negative parameter $Q$. We find that, if at least one of the fluids has nonvanishing chemical potential, for instance ${\mu }_x<0$ and ${\mu }_{\mathrm{dm}}=0$ or ${\mu }_x=0$ and ${\mu }_{\mathrm{dm}}>0$, the decay is possible, where ${\mu }_x$ and ${\mu }_{\mathrm{dm}}$ are the chemical potentials of dark energy and dark matter, respectively. Using recent cosmological data, we find that, for a fairly simple interaction, the dark matter decay is favored with a probability of $\sim 93\%$ over the dark energy decay. This result comes from a likelihood analysis where only background evolution has been considered.

Figure 1

a) Plane ${\Omega }_m\mathrm{\text{−}}\epsilon$ showing the 68.3%, 95.4%, and 99.7% contours of probability, as well as the $\epsilon =0$ line (dashed line). b) Marginalized likelihood, normalized at the peak (solid line) and CDF (long-dashed line) for the $\epsilon$ parameter, as well as the $\epsilon =0$ line (short-dashed line) and $P(\epsilon >0)$ line (dotted line). See text for details.