Scalar dark energy models mimicking $\Lambda$CDM with arbitrary future evolution

TL;DR

This paper explores scalar dark energy models that closely mimic the $\Lambda$CDM model yet diverge in the future, leading to various possible cosmic end states, and shows they are consistent with current observations.

Contribution

It introduces a class of dark energy models with arbitrary future evolution that are compatible with current data and analyzes their stability and potential future singularities.

Findings

Models are compatible with current astronomical data.

Different future evolutions include de-Sitter, Little Rip, and finite-time singularities.

Models remain stable for billions of years before diverging or ending in singularities.

Abstract

Dark energy models with various scenarios of evolution are considered from the viewpoint of the formalism for the equation of state. It is shown that these models are compatible with current astronomical data. Some of the models presented here evolve arbitrarily close to $\Lambda$CDM up to the present, but diverge in the future into a number of different possible asymptotic states, including asymptotic de-Sitter (pseudo-rip) evolution, little rips with disintegration of bound structures, and various forms of finite-time future singularities. Therefore it is impossible from observational data to determine whether the universe will end in a future singularity or not. We demonstrate that the models under consideration are stable for a long period of time (billions of years) before entering a Little Rip/Pseudo-Rip induced dissolution of bound structures or before entering a soft finite-time future singularity. Finally, the physical consequences of Little Rip, Type II, III and Big Crush singularities are briefly compared.