Expansion History with Decaying Vacuum: A Complete Cosmological Scenario

TL;DR

This paper introduces a comprehensive cosmological model where the universe evolves from an initial de Sitter phase through radiation, matter, and dark energy epochs, using a dynamical vacuum energy that avoids singularities and aligns with observed cosmic history.

Contribution

It presents a novel cosmological scenario with a dynamical vacuum energy density that naturally transitions through all major cosmic epochs, providing a complete and singularity-free expansion history.

Findings

Avoids initial singularity with a pure de Sitter start

Provides a natural graceful exit from inflation

Aligns closely with the standard LCDM model at late times

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 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.