Pichler, Sebastian (2005): Scalar fields and higher-derivative gravity in brane worlds. Dissertation, LMU München: Faculty of Physics |

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**DOI**: 10.5282/edoc.3634

### Abstract

We consider the brane world picture in the context of higher-derivative theories of gravity and tackle the problematic issues fine-tuning and brane-embedding. First, we give an overview of extra-dimensional physics, from the Kaluza-Klein picture up to modern brane worlds with large extra dimensions. We describe the different models and their physical impact on future experiments. We work within the framework of Randall-Sundrum models in which the brane is a gravitating object, which warps the background metric. We add scalar fields to the original model and find new and self-consistent solutions for quadratic potentials of the fields. This gives us the tools to investigate higher-derivative gravity theories in brane world models. Specifically, we take gravitational Lagrangians that depend on an arbitrary function of the Ricci scalar only, so-called $f(R)$-gravity. We make use of the conformal equivalence between $f(R)$-gravity and Einstein-Hilbert gravity with an auxiliary scalar field. We find that the solutions in the higher-derivative gravity framework behave very differently from the original Randall-Sundrum model: the metric functions do not have the typical kink across the brane. Furthermore, we present solutions that do not rely on a cosmological constant in the bulk and so avoid the fine-tuning problem. We address the issue of brane-embedding, which is important in perturbative analyses. We consider the embedding of codimension one hypersurfaces in general and derive a new equation of motion with which the choice for the embedding has to comply. In particular, this allows for a consistent consideration of brane world perturbations in the case of higher-derivative gravity. We use the newly found background solutions for quadratic potentials and find that gravity is still effectively localized on the brane, i.e that the Newtonian limit holds.

Item Type: | Theses (Dissertation, LMU Munich) |
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Keywords: | gravitation, brane worlds, higher-derivative gravity, scalar field |

Subjects: | 500 Natural sciences and mathematics 500 Natural sciences and mathematics > 530 Physics |

Faculties: | Faculty of Physics |

Language: | English |

Date of oral examination: | 2. May 2005 |

1. Referee: | Mukhanov, Viatcheslav |

MD5 Checksum of the PDF-file: | 4b829e6686d9b7fa6eb79618f2ad4f85 |

Signature of the printed copy: | 0001/UMC 14578 |

ID Code: | 3634 |

Deposited On: | 02. Jun 2005 |

Last Modified: | 24. Oct 2020 10:31 |