## Özet

We present an explicit detailed theoretical and observational investigation of an anisotropic massive Brans–Dicke (BD) gravity extension of the standard Λ CDM model, wherein the extension is characterized by two additional degrees of freedom; the BD parameter, ω, and the present day density parameter corresponding to the shear scalar, Ωσ2,0. The BD parameter, determining the deviation from general relativity (GR), by alone characterizes both the dynamics of the effective dark energy (DE) and the redshift dependence of the shear scalar. These two affect each other depending on ω, namely, the shear scalar contributes to the dynamics of the effective DE, and its anisotropic stress – which does not exist in scalar field models of DE within GR – controls the dynamics of the shear scalar deviating from the usual ∝ (1 + z) ^{6} form in GR. We mainly confine the current work to non-negative ω values as it is the right sign – theoretically and observationally – for investigating the model as a correction to the Λ CDM. By considering the current cosmological observations, we find that ω≳ 250 , Ωσ2,0≲10-23 and the contribution of the anisotropy of the effective DE to this value is insignificant. We conclude that the simplest anisotropic massive BD gravity extension of the standard Λ CDM model exhibits no significant deviations from it all the way to the Big Bang Nucleosynthesis. We also point out the interesting features of the model in the case of negative ω values; for instance, the constraints on Ωσ2,0 could be relaxed considerably, the values of ω∼ - 1 (relevant to string theories) predict dramatically different dynamics for the expansion anisotropy.

Orijinal dil | İngilizce |
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Makale numarası | 32 |

Dergi | European Physical Journal C |

Hacim | 80 |

Basın numarası | 1 |

DOI'lar | |

Yayın durumu | Yayınlandı - 1 Oca 2020 |

### Bibliyografik not

Publisher Copyright:© 2020, The Author(s).

### Finansman

The authors thank to Shahin Sheikh-Jabbari, Mehmet Özkan and Suresh Kumar for valuable discussions. Ö.A. acknowledges the support of the Turkish Academy of Sciences in scheme of the Outstanding Young Scientist Award (TÜBA-GEBİP). Ö.A. is grateful for the hospitality of the Abdus Salam International Center for Theoretical Physics (ICTP) while the part of this research was being carried out. N.K. acknowledges the post-doctoral research support from the İstanbul Technical University (ITU). J.A.V. acknowledges the support provided by the grants FOSEC SEP-CONACYT Investigación Básica A1-S-21925, and UNAM-PAPIIT IA102219. The authors thank to Shahin Sheikh-Jabbari, Mehmet ?zkan and Suresh Kumar for valuable discussions. ?.A. acknowledges the support of the Turkish Academy of Sciences in scheme of the Outstanding Young Scientist Award (T?BA-GEB?P). ?.A. is grateful for the hospitality of the Abdus Salam International Center for Theoretical Physics (ICTP) while the part of this research was being carried out. N.K. acknowledges the post-doctoral research support from the ?stanbul Technical University (ITU). J.A.V. acknowledges the support provided by the grants FOSEC SEP-CONACYT Investigaci?n B?sica A1-S-21925, and UNAM-PAPIIT IA102219.

Finansörler | Finansör numarası |
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FOSEC SEP-CONACYT | UNAM-PAPIIT IA102219, A1-S-21925 |

Technical University | |

TÜBA-GEBİP | |

International Technological University | |

Abdus Salam International Centre for Theoretical Physics | |

Türkiye Bilimler Akademisi | T?BA-GEB?P |

Istanbul Teknik Üniversitesi |