  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 dynamical
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. Since the
resulting late time cosmic history is very close to the concordance LCDM model,
the new unified framework embodies a more complete past cosmic evolution than
the standard cosmology.
