### Abstract

We discuss the realization of inflation and resulting cosmological perturbations in the low-energy effective string theory. In order to obtain nearly scale-invariant spectra of density perturbations and a suppressed tensor-to-scalar ratio, it is generally necessary that the dilaton field is effectively decoupled from gravity together with the existence of a slowly varying dilaton potential. We also study the effect of second-order corrections to the tree-level action which are the sum of a Gauss-Bonnet term coupled to and a kinetic term ( )4. We find that it is possible to realize observationally supported spectra of scalar and tensor perturbations provided that the correction is dominated by the ( )4 term even in the absence of the dilaton potential. When the Gauss-Bonnet term is dominant, tensor perturbations exhibit violent negative instabilities on small scales about a de Sitter background in spite of the fact that scale-invariant scalar perturbations can be achieved.

Original language | English |
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Article number | 023520 |

Journal | Physical Review D - Particles, Fields, Gravitation and Cosmology |

Volume | 75 |

Issue number | 2 |

DOIs | |

Publication status | Published - 2007 |

Externally published | Yes |

### ASJC Scopus subject areas

- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)