## Abstract

Some features of the Bianchi type-I universes in the presence of a fluid that wields an anisotropic equation of state (EoS) parameter are discussed in the context of general relativity. The models that exhibit de Sitter volumetric expansion due to the constant effective energy density (the sum of the energy density of the fluid and the anisotropy energy density) are of particular interest. We also introduce two locally rotationally symmetric models, which exhibit de Sitter volumetric expansion in the presence of a hypothetical fluid that has been obtained by minimally altering the conventional vacuum energy. In the first model, the directional EoS parameter on the x axis is assumed to be -1, while the ones on the other axes and the energy density of the fluid are allowed to be functions of time. In the second model, the energy density of the fluid is assumed to be constant, while the directional EoS parameters are allowed to be functions of time.

Original language | English |
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Pages (from-to) | 315-322 |

Number of pages | 8 |

Journal | Astrophysics and Space Science |

Volume | 326 |

Issue number | 2 |

DOIs | |

Publication status | Published - 2010 |

Externally published | Yes |

### Funding

Acknowledgements Özgür Akarsu was supported in part by The Scientific and Technological Research Council of Turkey (TÜB˙TAK). Some of this work was carried out while Ö. Akarsu was visiting the Department of Applied Mathematics and Theoretical Physics (DAMTP), University of Cambridge. Ö. Akarsu would also like to thank Jonathan Middleton for the discussions he had with him.

Funders | Funder number |
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Türkiye Bilimsel ve Teknolojik Araştirma Kurumu |

## Keywords

- Anisotropic fluid
- Bianchi type-I
- Cosmological constant
- De Sitter expansion