### Abstract

In a recent paper,^{1} we have shown that f(R) = R + μR ^{n} modified gravity dark energy models are not cosmologically viable because during the matter era that precedes the accelerated stage the cosmic expansion is given by a ∼ t^{1/2} rather than a ∼ t ^{2/3}, where a is a scale factor and t is the cosmic time. A recent work by Capozziello et al.^{2} criticized our results presenting some apparent counter-examples to our claim in f(R) = μR^{n} models. We show here that those particular R^{n} models can produce an expansion as a ∼ t^{2/3} but this does not connect to a late-time acceleration. Hence, though acceptable f(R) dark energy models might exist, the R^{n} models presented in Capozziello et al. are not cosmologically viable, confirming our previous results in Ref. 1.

Original language | English |
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Pages (from-to) | 1555-1561 |

Number of pages | 7 |

Journal | International Journal of Modern Physics D |

Volume | 16 |

Issue number | 10 |

DOIs | |

Publication status | Published - 2007 Oct |

Externally published | Yes |

### Keywords

- Dark energy
- Modified gravity

### ASJC Scopus subject areas

- Mathematical Physics
- Astronomy and Astrophysics
- Space and Planetary Science

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## Cite this

*International Journal of Modern Physics D*,

*16*(10), 1555-1561. https://doi.org/10.1142/S0218271807010936