### Abstract

Quantum fluctuations of an inflaton field, slow rolling during inflation are coupled to metric fluctuations. In conventional four-dimensional cosmology one can calculate the effect of scalar metric perturbations as slow-roll corrections to the evolution of a massless free field in de Sitter spacetime. This gives the well-known first-order corrections to the field perturbations after horizon exit. If inflaton fluctuations on a four-dimensional brane embedded in a five-dimensional bulk spacetime are studied to first order in slow roll, then we recover the usual conserved curvature perturbation on superhorizon scales. But on small scales, at high energies, we find that the coupling to the bulk metric perturbations cannot be neglected, leading to a modified amplitude of vacuum oscillations on small scales. This is a large effect which casts doubt on the reliability of the usual calculation of inflaton fluctuations on the brane neglecting their gravitational coupling.

Original language | English |
---|---|

Pages (from-to) | 153-175 |

Number of pages | 23 |

Journal | Journal of Cosmology and Astroparticle Physics |

Issue number | 8 |

DOIs | |

Publication status | Published - 2005 Aug 1 |

### Fingerprint

### Keywords

- Cosmological perturbation theory
- Cosmology with extra dimensions
- Inflation

### ASJC Scopus subject areas

- Physics and Astronomy(all)

### Cite this

*Journal of Cosmology and Astroparticle Physics*, (8), 153-175. https://doi.org/10.1088/1475-7516/2005/08/009

**Slow-roll corrections to inflaton fluctuations on a brane.** / Koyama, Kazuya; Mizuno, Shuntaro; Wands, David.

Research output: Contribution to journal › Article

*Journal of Cosmology and Astroparticle Physics*, no. 8, pp. 153-175. https://doi.org/10.1088/1475-7516/2005/08/009

}

TY - JOUR

T1 - Slow-roll corrections to inflaton fluctuations on a brane

AU - Koyama, Kazuya

AU - Mizuno, Shuntaro

AU - Wands, David

PY - 2005/8/1

Y1 - 2005/8/1

N2 - Quantum fluctuations of an inflaton field, slow rolling during inflation are coupled to metric fluctuations. In conventional four-dimensional cosmology one can calculate the effect of scalar metric perturbations as slow-roll corrections to the evolution of a massless free field in de Sitter spacetime. This gives the well-known first-order corrections to the field perturbations after horizon exit. If inflaton fluctuations on a four-dimensional brane embedded in a five-dimensional bulk spacetime are studied to first order in slow roll, then we recover the usual conserved curvature perturbation on superhorizon scales. But on small scales, at high energies, we find that the coupling to the bulk metric perturbations cannot be neglected, leading to a modified amplitude of vacuum oscillations on small scales. This is a large effect which casts doubt on the reliability of the usual calculation of inflaton fluctuations on the brane neglecting their gravitational coupling.

AB - Quantum fluctuations of an inflaton field, slow rolling during inflation are coupled to metric fluctuations. In conventional four-dimensional cosmology one can calculate the effect of scalar metric perturbations as slow-roll corrections to the evolution of a massless free field in de Sitter spacetime. This gives the well-known first-order corrections to the field perturbations after horizon exit. If inflaton fluctuations on a four-dimensional brane embedded in a five-dimensional bulk spacetime are studied to first order in slow roll, then we recover the usual conserved curvature perturbation on superhorizon scales. But on small scales, at high energies, we find that the coupling to the bulk metric perturbations cannot be neglected, leading to a modified amplitude of vacuum oscillations on small scales. This is a large effect which casts doubt on the reliability of the usual calculation of inflaton fluctuations on the brane neglecting their gravitational coupling.

KW - Cosmological perturbation theory

KW - Cosmology with extra dimensions

KW - Inflation

UR - http://www.scopus.com/inward/record.url?scp=24644522777&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=24644522777&partnerID=8YFLogxK

U2 - 10.1088/1475-7516/2005/08/009

DO - 10.1088/1475-7516/2005/08/009

M3 - Article

SP - 153

EP - 175

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 8

ER -