## Abstract

Scale-independent EMSG is a particular model of energy–momentum squared gravity (EMSG) in which the new terms in the Einstein field equations arising from the EMSG theory enter with the same power as the usual terms from Einstein–Hilbert part of the action. However, the model violates the local energy–momentum conservation and matter-current conservation in general and hence, permits a process of matter creation/annihilation in an expanding universe. Consequently, the scale factor dependencies of the energy densities are modified by the dimensionless model parameter α. We revisit some nostalgias such as static universes and de Sitter/steady state universes. We reproduce the original ones, moreover, present some novelties, e.g., a spatially flat static universe, de Sitter expansion by negative vacuum energy, steady state universes in the presence of arbitrary fluids with constant equation of state (EoS) parameter other than dust, etc. We also investigate the possible dynamics of dust dominated and radiation dominated universes. Depending on the value of α, dust/radiation dominated universe exhibits power-law accelerated/decelerated expansion, corresponds to a steady state model or may end in a big rip. In the framework of anisotropic cosmology, we reproduce Barrow's quiescent universe in the presence of stiff fluid and extend it to fluids with arbitrary constant EoS parameter. We also relax the condition for isotropic initial singularity (big bang) owing to that EMSG effectively allows ultra-stiff EoS parameters.

Original language | English |
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Article number | 101194 |

Journal | Physics of the Dark Universe |

Volume | 40 |

DOIs | |

Publication status | Published - May 2023 |

### Bibliographical note

Publisher Copyright:© 2023 Elsevier B.V.

### Funding

Ö.A. acknowledges the support by the Turkish Academy of Sciences, Turkey in the scheme of the Outstanding Young Scientist Award (TÜBA-GEBİP), and the COST ActionCA21136 (CosmoVerse). N.M.U. is supported by Boğaziçi University Research Fund Grant Number 18541P. Ö.A. acknowledges the support by the Turkish Academy of Sciences, Turkey in the scheme of the Outstanding Young Scientist Award ( TÜBA-GEBİP ), and the COST Action CA21136 (CosmoVerse). N.M.U. is supported by Boğaziçi University Research Fund Grant Number 18541P .

Funders | Funder number |
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COST ActionCA21136 | |

TÜBA-GEBİP | |

European Cooperation in Science and Technology | CA21136 |

Türkiye Bilimler Akademisi | |

Boğaziçi Üniversitesi | 18541P |

## Keywords

- Accelerated expansion of the universe
- Anisotropic expansion
- Big Rip
- Cosmological models
- De Sitter universe
- Energy-momentum squared gravity
- Initial singularity
- Quiescent universe
- Static universe
- Steady state universe