# Perturbations in a regular bouncing universe

## Abstract

We consider a simple toy model of a regular bouncing universe. The bounce is caused by an extra timelike dimension, which leads to a sign flip of the {rho}{sup 2} term in the effective four dimensional Randall Sundrum-like description. We find a wide class of possible bounces: big bang avoiding ones for regular matter content, and big rip avoiding ones for phantom matter. Focusing on radiation as the matter content, we discuss the evolution of scalar, vector and tensor perturbations. We compute a spectral index of n{sub s}=-1 for scalar perturbations and a deep blue index for tensor perturbations after invoking vacuum initial conditions, ruling out such a model as a realistic one. We also find that the spectrum (evaluated at Hubble crossing) is sensitive to the bounce. We conclude that it is challenging, but not impossible, for cyclic/ekpyrotic models to succeed, if one can find a regularized version.

- Authors:

- Physics Department, Brown University, Providence, Rhode Island 02912 (United States)
- University of Wisconsin, Madison, Wisconsin 53706 (United States)

- Publication Date:

- OSTI Identifier:
- 20782647

- Resource Type:
- Journal Article

- Resource Relation:
- Journal Name: Physical Review. D, Particles Fields; Journal Volume: 73; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevD.73.064013; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; COSMOLOGY; DISTURBANCES; EVOLUTION; INDEXES; MATTER; SCALARS; UNIVERSE; VECTORS

### Citation Formats

```
Battefeld, T.J., and Geshnizjani, G.
```*Perturbations in a regular bouncing universe*. United States: N. p., 2006.
Web. doi:10.1103/PHYSREVD.73.064013.

```
Battefeld, T.J., & Geshnizjani, G.
```*Perturbations in a regular bouncing universe*. United States. doi:10.1103/PHYSREVD.73.064013.

```
Battefeld, T.J., and Geshnizjani, G. Wed .
"Perturbations in a regular bouncing universe". United States.
doi:10.1103/PHYSREVD.73.064013.
```

```
@article{osti_20782647,
```

title = {Perturbations in a regular bouncing universe},

author = {Battefeld, T.J. and Geshnizjani, G.},

abstractNote = {We consider a simple toy model of a regular bouncing universe. The bounce is caused by an extra timelike dimension, which leads to a sign flip of the {rho}{sup 2} term in the effective four dimensional Randall Sundrum-like description. We find a wide class of possible bounces: big bang avoiding ones for regular matter content, and big rip avoiding ones for phantom matter. Focusing on radiation as the matter content, we discuss the evolution of scalar, vector and tensor perturbations. We compute a spectral index of n{sub s}=-1 for scalar perturbations and a deep blue index for tensor perturbations after invoking vacuum initial conditions, ruling out such a model as a realistic one. We also find that the spectrum (evaluated at Hubble crossing) is sensitive to the bounce. We conclude that it is challenging, but not impossible, for cyclic/ekpyrotic models to succeed, if one can find a regularized version.},

doi = {10.1103/PHYSREVD.73.064013},

journal = {Physical Review. D, Particles Fields},

number = 6,

volume = 73,

place = {United States},

year = {Wed Mar 15 00:00:00 EST 2006},

month = {Wed Mar 15 00:00:00 EST 2006}

}