Multi-horizon spherically symmetric spacetimes with several scales of vacuum energy

TL;DR

This paper introduces a family of spherically symmetric, multi-horizon cosmological models with evolving vacuum energy scales, describing a universe with multiple phase transitions and horizons, consistent with observational data.

Contribution

It presents a novel class of anisotropic, inhomogeneous spacetimes with multiple vacuum energy scales, including detailed analysis of a three-scale model aligned with cosmological observations.

Findings

The universe in the model has three horizons.

The model describes a universe with multiple vacuum energy phase transitions.

The universe's evolution includes irreversible expansion phases.

Abstract

We present a family of spherically symmetric multi-horizon spacetimes with a vacuum dark fluid, associated with a time-dependent and spatially inhomogeneous cosmological term. The vacuum dark fluid is defined in a model-independent way by the symmetry of its stress-energy tensor, i.e., its invariance under Lorentz boosts in a distinguished spatial direction ($p_r=-\rho$ for spherical symmetry), which makes the dark fluid essentially anisotropic and allows its density to evolve. The related cosmological models belong to the Lemaitre class of models with anisotropic fluids and describe a universe with several scales of vacuum energy related to phase transitions during its evolution. The typical behavior of solutions and the number of spacetime horizons are determined by the number of vacuum scales. We study in detail a model with three vacuum scales: GUT, QCD and that responsible for the present accelerated expansion. The model parameters are fixed by the observational data and by analyticity and causality conditions. We find that our Universe has three horizons. During the first inflation the Universe enters a T-region which makes the expansion irreversible. After the second phase transition at the QCD scale the Universe enters an R-region, where for a long time its geometry remains almost pseudo-Euclidean. After crossing the third horizon related to the present vacuum density, the Universe should enter the next T-region with inevitable expansion.