From de Sitter to de Sitter: A non-singular inflationary universe driven by vacuum

TL;DR

This paper proposes a non-singular, inflationary universe model driven by vacuum energy decay, featuring a phase transition that produces radiation and leads to a late-time de Sitter universe, avoiding initial singularities.

Contribution

It introduces a semi-classical vacuum energy decay model that results in a non-singular, inflationary universe with a phase transition and realistic late-time behavior.

Findings

No initial singularity; universe exists since infinite past.

Phase transition causes rapid decrease in H and Lambda, producing radiation.

Late-time universe resembles standard cosmological model with de Sitter expansion.

Abstract

A semi-classical analysis of vacuum energy in the expanding spacetime suggests that the cosmological term decays with time, with a concomitant matter production. For early times we find, in Planck units, $\Lambda \approx H^4$, where H is the Hubble parameter. The corresponding cosmological solution has no initial singularity, existing since an infinite past. During an infinitely long period we have a quasi-de Sitter, inflationary universe, with $H \approx 1$. However, at a given time, the expansion undertakes a phase transition, with H and $\Lambda$ decreasing to nearly zero in a few Planck times, producing a huge amount of radiation. On the other hand, the late-time scenario is similar to the standard model, with the radiation phase followed by a dust era, which tends asymptotically to a de Sitter universe, with vacuum dominating again.