The screening Horndeski cosmologies
Alexei A. Starobinsky, Sergey V. Sushkov, Mikhail S. Volkov

TL;DR
This paper systematically analyzes cosmological solutions in a specific Horndeski model with Galileon symmetry, identifying stable late-time accelerating solutions but finding all past solutions unstable, limiting its cosmological applicability.
Contribution
It provides a comprehensive classification of solutions in the Fab Five Horndeski model, including ghost-free branches and stability analysis, highlighting limitations for complete cosmological modeling.
Findings
Identifies ghost-free late-time accelerating solutions.
All solutions are unstable near the initial singularity.
The model may describe current acceleration but not the entire history.
Abstract
We present a systematic analysis of homogeneous and isotropic cosmologies in a particular Horndeski model with Galileon shift symmetry, containing also a -term and a matter. The model, sometimes called Fab Five, admits a rich spectrum of solutions. Some of them describe the standard late time cosmological dynamic dominated by the -term and matter, while at the early times the universe expands with a constant Hubble rate determined by the value of the scalar kinetic coupling. For other solutions the -term and matter are screened at all times but there are nevertheless the early and late accelerating phases. The model also admits bounces, as well as peculiar solutions describing "the emergence of time". Most of these solutions contain ghosts in the scalar and tensor sectors. However, a careful analysis reveals three different branches of ghost-free solutions,…
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