# Conserved cosmological perturbation in Galileon models

## Abstract

We prove the existence of a fully nonlinear conserved curvature perturbation on large scales in Galileon-type scalar field models in two approaches. The first approach is based on the conservation of energy-momentum tensor of the Galileon field, which is also the familiar approach in understanding the conservation in k-essence or perfect fluid models. We show that the fluid corresponding to the Galileon field becomes perfect and barotropic on large scales, which is responsible to the conservation. The difference from k-essence model is that, besides the energy-momentum conservation, the Einstein equation must be employed in order to complete the proof of barotropy. In the second approach, we derive the fully non-perturbative action for the curvature perturbation ζ in Galileon models on large scales, and argue that ζ = const is indeed an exact solution on large scales. This conservation of curvature perturbation is important since it relates the later and the primordial universe.

- Authors:

- Astroparticule et Cosmologie (APC), UMR 7164-CNRS, Université Denis Diderot-Paris 7, 10 rue Alice Domon et Léonie Duquet, 75205 Paris (France)
- (LPTENS), 24 rue Lhomond, 75231 Paris (France)
- (IAP), UMR 7095-CNRS, Université Pierre et Marie Curie-Paris 6, 98bis Boulevard Arago, 75014 Paris (France)

- Publication Date:

- OSTI Identifier:
- 22280232

- Resource Type:
- Journal Article

- Journal Name:
- Journal of Cosmology and Astroparticle Physics

- Additional Journal Information:
- Journal Volume: 2011; Journal Issue: 10; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1475-7516

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; COSMOLOGY; DISTURBANCES; EINSTEIN FIELD EQUATIONS; ENERGY-MOMENTUM TENSOR; EXACT SOLUTIONS; NONLINEAR PROBLEMS; SCALAR FIELDS; UNIVERSE

### Citation Formats

```
Gao, Xian, E-mail: xgao@apc.univ-paris7.fr, Laboratoire de Physique Théorique, École Normale Supérieure, and Institut d'Astrophysique de Paris.
```*Conserved cosmological perturbation in Galileon models*. United States: N. p., 2011.
Web. doi:10.1088/1475-7516/2011/10/021.

```
Gao, Xian, E-mail: xgao@apc.univ-paris7.fr, Laboratoire de Physique Théorique, École Normale Supérieure, & Institut d'Astrophysique de Paris.
```*Conserved cosmological perturbation in Galileon models*. United States. doi:10.1088/1475-7516/2011/10/021.

```
Gao, Xian, E-mail: xgao@apc.univ-paris7.fr, Laboratoire de Physique Théorique, École Normale Supérieure, and Institut d'Astrophysique de Paris. Sat .
"Conserved cosmological perturbation in Galileon models". United States. doi:10.1088/1475-7516/2011/10/021.
```

```
@article{osti_22280232,
```

title = {Conserved cosmological perturbation in Galileon models},

author = {Gao, Xian, E-mail: xgao@apc.univ-paris7.fr and Laboratoire de Physique Théorique, École Normale Supérieure and Institut d'Astrophysique de Paris},

abstractNote = {We prove the existence of a fully nonlinear conserved curvature perturbation on large scales in Galileon-type scalar field models in two approaches. The first approach is based on the conservation of energy-momentum tensor of the Galileon field, which is also the familiar approach in understanding the conservation in k-essence or perfect fluid models. We show that the fluid corresponding to the Galileon field becomes perfect and barotropic on large scales, which is responsible to the conservation. The difference from k-essence model is that, besides the energy-momentum conservation, the Einstein equation must be employed in order to complete the proof of barotropy. In the second approach, we derive the fully non-perturbative action for the curvature perturbation ζ in Galileon models on large scales, and argue that ζ = const is indeed an exact solution on large scales. This conservation of curvature perturbation is important since it relates the later and the primordial universe.},

doi = {10.1088/1475-7516/2011/10/021},

journal = {Journal of Cosmology and Astroparticle Physics},

issn = {1475-7516},

number = 10,

volume = 2011,

place = {United States},

year = {2011},

month = {10}

}