Expansion history with decaying vacuum: a complete cosmological scenario

Abstract

We propose a novel cosmological scenario with the space-time emerging from a pure initial de Sitter stage and subsequently evolving into the radiation, matter and dark energy dominated epochs, thereby avoiding the initial singularity and providing a complete description of the expansion history and a natural solution to the horizon problem.The model is based on a running vacuum energy density which evolves as a power series of the Hubble rate. The transit from the inflation into the standard radiation epoch is universal, giving a clue for a successful description of the graceful exit.The Universe is finally driven into the present slow accelerated expansion, characterized by a residual (but dynamical) vacuum energy. While the resulting late time cosmic history is very close to the cosmic concordance model, the new framework embodies a more complete past cosmic evolution than the standard cosmology.