Cosmological solutions to the semiclassical Einstein equation

Abstract: We will discuss some newly found solutions to the full massless semiclassical Einstein equation (SCE) in a cosmological setting. For this purpose we first present the SCE in a certain formulation in which the chosen state of the quantum field has a particularly simple shape. The choice of these states is motivated by an observation on the Minkowski vacuum state on a flat space-time. Therewith we can solve the SCE with a numerical solver and, at least generically, obtain solutions which well fit physical expectations. Moreover, these solutions indicate dark energy as a quantum effect on cosmological metrics and, since in our model both mass and cosmological constant vanish, this may not be traced back to the usual, obvious dark-energy/cosmological constant effect of a quantum field. Finally, we suggest a possibility how to include an inflationary phase to the semiclassical cosmological expansion by reintroducing a cosmological constant, which works both with the above 'Minkowski-like' state and the Bunch-Davies state.