# Generalized galilean genesis

## Abstract

The galilean genesis scenario is an alternative to inflation in which the universe starts expanding from Minkowski in the asymptotic past by violating the null energy condition stably. Several concrete models of galilean genesis have been constructed so far within the context of galileon-type scalar-field theories. We give a generic, unified description of the galilean genesis scenario in terms of the Horndeski theory, i.e., the most general scalar-tensor theory with second-order field equations. In doing so we generalize the previous models to have a new parameter (denoted by α) which results in controlling the evolution of the Hubble rate. The background dynamics is investigated to show that the generalized galilean genesis solution is an attractor, similarly to the original model. We also study the nature of primordial perturbations in the generalized galilean genesis scenario. In all the models described by our generalized genesis Lagrangian, amplification of tensor perturbations does not occur as opposed to what happens in quasi-de Sitter inflation. We show that the spectral index of curvature perturbations is determined solely from the parameter α and does not depend on the other details of the model. In contrast to the original model, a nearly scale-invariant spectrum of curvature perturbationsmore »

- Authors:

- Department of Physics, Rikkyo University, Toshima, Tokyo 175-8501 (Japan)

- Publication Date:

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

- OSTI Identifier:
- 22454534

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2015; Journal Issue: 03; Other Information: PUBLISHER-ID: JCAP03(2015)057; OAI: oai:repo.scoap3.org:9786; 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:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ASYMPTOTIC SOLUTIONS; ATTRACTORS; COSMOLOGICAL INFLATION; DE SITTER SPACE; FIELD EQUATIONS; HUBBLE EFFECT; LAGRANGIAN FUNCTION; MINKOWSKI SPACE; PERTURBATION THEORY; SCALAR FIELDS; SCALARS; SPECTRA; UNIVERSE

### Citation Formats

```
Nishi, Sakine, and Kobayashi, Tsutomu.
```*Generalized galilean genesis*. United States: N. p., 2015.
Web. doi:10.1088/1475-7516/2015/03/057.

```
Nishi, Sakine, & Kobayashi, Tsutomu.
```*Generalized galilean genesis*. United States. doi:10.1088/1475-7516/2015/03/057.

```
Nishi, Sakine, and Kobayashi, Tsutomu. Tue .
"Generalized galilean genesis". United States.
doi:10.1088/1475-7516/2015/03/057.
```

```
@article{osti_22454534,
```

title = {Generalized galilean genesis},

author = {Nishi, Sakine and Kobayashi, Tsutomu},

abstractNote = {The galilean genesis scenario is an alternative to inflation in which the universe starts expanding from Minkowski in the asymptotic past by violating the null energy condition stably. Several concrete models of galilean genesis have been constructed so far within the context of galileon-type scalar-field theories. We give a generic, unified description of the galilean genesis scenario in terms of the Horndeski theory, i.e., the most general scalar-tensor theory with second-order field equations. In doing so we generalize the previous models to have a new parameter (denoted by α) which results in controlling the evolution of the Hubble rate. The background dynamics is investigated to show that the generalized galilean genesis solution is an attractor, similarly to the original model. We also study the nature of primordial perturbations in the generalized galilean genesis scenario. In all the models described by our generalized genesis Lagrangian, amplification of tensor perturbations does not occur as opposed to what happens in quasi-de Sitter inflation. We show that the spectral index of curvature perturbations is determined solely from the parameter α and does not depend on the other details of the model. In contrast to the original model, a nearly scale-invariant spectrum of curvature perturbations is obtained for a specific choice of α.},

doi = {10.1088/1475-7516/2015/03/057},

journal = {Journal of Cosmology and Astroparticle Physics},

number = 03,

volume = 2015,

place = {United States},

year = {Tue Mar 31 00:00:00 EDT 2015},

month = {Tue Mar 31 00:00:00 EDT 2015}

}