# The screening Horndeski cosmologies

## Abstract

We present a systematic analysis of homogeneous and isotropic cosmologies in a particular Horndeski model with Galileon shift symmetry, containing also a Λ-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 Λ-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 Λ-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, all showing a late time acceleration phase. We analyse the dynamical stability of these solutions and find that all of them are stable in the future, since all their perturbations stay bounded at late times. However, they all turn out to be unstable in the past, as their perturbations grow violently when one approaches the initial spacetime singularity. We therefore conclude that the modelmore »

- Authors:

- L.D. Landau Institute for Theoretical Physics RAS,Moscow 119334 (Russian Federation)
- (Russian Federation)
- Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan (Russian Federation)
- Laboratoire de Mathématiques et Physique Théorique CNRS-UMR 7350,Université de Tours,Parc de Grandmont, 37200 Tours (France)

- Publication Date:

- Sponsoring Org.:
- SCOAP3, CERN, Geneva (Switzerland)

- OSTI Identifier:
- 22572090

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2016; Journal Issue: 06; Other Information: PUBLISHER-ID: JCAP06(2016)007; OAI: oai:repo.scoap3.org:15894; cc-by Article funded by SCOAP3. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 License. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COSMOLOGICAL CONSTANT; COSMOLOGY; COUPLING; DISTURBANCES; MATHEMATICAL SOLUTIONS; NONLUMINOUS MATTER; PERTURBATION THEORY; SCALAR FIELDS; TENSOR FIELDS

### Citation Formats

```
Starobinsky, Alexei A., Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan, Sushkov, Sergey V., Volkov, Mikhail S., and Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan.
```*The screening Horndeski cosmologies*. United States: N. p., 2016.
Web. doi:10.1088/1475-7516/2016/06/007.

```
Starobinsky, Alexei A., Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan, Sushkov, Sergey V., Volkov, Mikhail S., & Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan.
```*The screening Horndeski cosmologies*. United States. doi:10.1088/1475-7516/2016/06/007.

```
Starobinsky, Alexei A., Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan, Sushkov, Sergey V., Volkov, Mikhail S., and Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan. Mon .
"The screening Horndeski cosmologies". United States.
doi:10.1088/1475-7516/2016/06/007.
```

```
@article{osti_22572090,
```

title = {The screening Horndeski cosmologies},

author = {Starobinsky, Alexei A. and Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan and Sushkov, Sergey V. and Volkov, Mikhail S. and Department of General Relativity and Gravitation, Institute of Physics,Kazan Federal University,Kremlevskaya street 18, 420008 Kazan},

abstractNote = {We present a systematic analysis of homogeneous and isotropic cosmologies in a particular Horndeski model with Galileon shift symmetry, containing also a Λ-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 Λ-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 Λ-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, all showing a late time acceleration phase. We analyse the dynamical stability of these solutions and find that all of them are stable in the future, since all their perturbations stay bounded at late times. However, they all turn out to be unstable in the past, as their perturbations grow violently when one approaches the initial spacetime singularity. We therefore conclude that the model has no viable solutions describing the whole of the cosmological history, although it may describe the current acceleration phase. We also check that the flat space solution is ghost-free in the model, but it may acquire ghost in more general versions of the Horndeski theory.},

doi = {10.1088/1475-7516/2016/06/007},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 06,

volume = 2016,

place = {United States},

year = {Mon Jun 06 00:00:00 EDT 2016},

month = {Mon Jun 06 00:00:00 EDT 2016}

}