Nonsingular Cosmology from an Interacting Vacuum

TL;DR

This paper explores nonsingular cosmological models with interacting vacuum energy and perfect fluids, demonstrating how such interactions can produce bouncing and cyclic universes with early and late accelerated phases.

Contribution

It introduces two specific models of vacuum-fluid interaction that lead to integrable dynamics and nonsingular cosmologies, including bouncing and cyclic solutions.

Findings

Bouncing solutions with early acceleration are possible in both models.

Cyclic universes can arise from the effective potential structure.

Models connect early bounce to late-time acceleration via matter-dominated era.

Abstract

We examine the dynamics of FLRW cosmologies in which the vacuum interacts with a perfect fluid through an energy exchange, focusing on the exploration of nonsingular configurations, including cyclic and bouncing models. We consider two specific choices for the energy transfer. In the first case, the energy transfer is proportional to a linear combination of the vacuum and fluid energy densities which makes the conservation equations exactly integrable. The resulting Friedmann equation can be interpreted as an energy constraint equation with an effective potential for the scale factor that may include an infinite barrier forcing a bounce at small values of the scale factor, as well as a potential well allowing for cycling solutions. In the second case, the energy transfer is a nonlinear combination of the vacuum and fluid energy densities. Nonetheless even in this case the dynamics can be partially integrated, leading to a first integral, reducing the number of degrees of freedom. We show that also in this nonlinear case bouncing and cycling cosmologies may arise. In both cases the structure of the resulting phase space allows for nonsingular orbits with an early accelerated phase around a single bounce, connected via a decelerated matter-dominated era to a late-time accelerated phase dominated by an effective cosmological constant.