Interacting vacuum energy in the dark sector
  We analyse three cosmological scenarios with interaction in the dark sector,
which are particular cases of a general expression for the energy flux from
vacuum to matter. In the first case the interaction leads to a transition from
an unstable de Sitter phase to a radiation dominated universe, avoiding in this
way the initial singularity. In the second case the interaction gives rise to a
slow-roll power-law inflation. Finally, the third scenario is a concordance
model for the late-time universe, with the vacuum term decaying into cold dark
matter. We identify the physics behind these forms of interaction and show that
they can be described as particular types of the modified Chaplygin gas.
