Complete Cosmic History with a dynamical Lambda(H) term

TL;DR

This paper introduces a class of dynamical vacuum energy models based on Lambda(H) that unify early inflation, matter and radiation eras, and late-time acceleration, providing solutions to cosmological puzzles without relying on traditional inflaton or cosmological constant models.

Contribution

The paper proposes a novel Lambda(H)-decaying vacuum model that naturally explains inflation, dark energy, and cosmic evolution, offering an alternative to standard LambdaCDM and inflaton theories.

Findings

Models reproduce the universe's accelerated expansion.

Smoothly connect initial and final de Sitter stages.

Align closely with the standard LambdaCDM expansion history.

Abstract

In the present mainstream cosmology, matter and spacetime emerged from a singularity and evolved through four distinct periods: early inflation, radiation, dark matter and late-time inflation (driven by dark energy). During the radiation and dark matter dominated stages, the universe is decelerating while the early and late-time inflations are accelerating stages. A possible connection between the accelerating periods remains unknown, and, even more intriguing, the best dark energy candidate powering the present accelerating stage (Lambda-vacuum) is plagued with the cosmological constant and coincidence puzzles. Here we propose an alternative solution for such problems based on a large class of time-dependent vacuum energy density models in the form of power series of the Hubble rate, Lambda=Lambda(H). The proposed class of Lambda(H)-decaying vacuum model provides: i) a new mechanism for inflation (different from the usual inflaton models), (ii) a natural mechanism for a graceful exit, which is universal for the whole class of models; iii) the currently accelerated expansion of the universe, iv) a mild dynamical dark energy at present; and v) a final de Sitter stage. Remarkably, the late-time cosmic expansion history of our class of models is very close to the concordance LambdaCDM model, but above all it furnishes the necessary smooth link between the initial and final de Sitter stages through the radiation- and matter-dominated epochs.