Coupled quintessence and vacuum decay

We discuss observational consequences of a class of cosmological models characterized by the dilution of pressureless matter attenuated with respect to the usual a(-3) scaling due to the decay of vacuum energy. We carry out a joint statistical analysis of observational data from the new gold sample of 182 SNe Ia, recent estimates of the cosmic microwave background shift parameter, and baryon acoustic oscillations measurements from the SDSS to show that such models favor the decay of vacuum only into the dark matter sector, and that the separately conserved baryons cannot be neglected. In order to explore ways to more fundamentally motivate these models, we also derive a coupled scalar field version for this general class of vacuum decay scenarios.