Entropy signature of the running cosmological constant

The renormalization group ( RG) improved cosmologies based upon a RG trajectory of quantum Einstein gravity ( QEG) with realistic parameter values are investigated using a system of cosmological evolution equations which allows for an unrestricted energy exchange between the vacuum and the matter sector. It is demonstrated that the scale dependence of the gravitational parameters, the cosmological constant in particular, leads to an entropy production in the matter system. The picture emerges that the Universe started out from a state of vanishing entropy, and that the radiation entropy observed today is essentially due to the coarse graining ( RG flow) in the quantum gravity sector which is related to the expansion of the Universe. Furthermore, the RG improved field equations are shown to possess solutions with an epoch of power law inflation immediately after the initial singularity. The ination is driven by the cosmological constant and ends automatically once the RG running has reduced the vacuum energy to the level of the matter energy density.