### Abstract

A recently investigated tachyonic scalar field dark energy dominated universe exhibits a bivalent future: Depending on initial parameters can run either into a De Sitter exponential expansion or into a traversable future soft singularity followed by a contraction phase. We also incluDe in the moDel (i) a tiny amount of radiation, (ii) baryonic matter (Ω_{bh}^{2} = 0.022161, where the Hubble constant is fixed as h = 0.706) and (iii) cold dark matter (CDM). Out of a variety of six types of evolutions arising in a more subtle classification, we iDentify two in which in the past the scalar field effectively Degenerates into a dust (its pressure drops to an insignificantly low negative value). These are the evolutions of type IIb converging to De Sitter and type III hitting the future soft singularity. We confront these background evolutions with various cosmological tests, including the supernova type Ia Union 2.1 data, baryon acoustic oscillation distance ratios, Hubble parameter-redshift relation and the cosmic microwave background (CMB) acoustic scale. We Determine a subset of the evolutions of both types which at 1σ confiDence level are consistent with all of these cosmological tests. At perturbative level we Derive the CMB temperature power spectrum to find the best agreement with the Planck data for Ω_{CDM} = 0.22. The fit is as good as for the ΛCDM moDel at high multipoles, but the power remains slightly overestimated at low multipoles, for both types of evolutions. The rest of the CDM is effectively generated by the tachyonic field, which in this sense acts as a combined dark energy and dark matter moDel.

Original language | English |
---|---|

Article number | 026 |

Journal | Journal of Cosmology and Astroparticle Physics |

Volume | 2014 |

Issue number | 11 |

DOIs | |

Publication status | Published - Nov 1 2014 |

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### Keywords

- cosmological perturbation theory
- dark energy theory

### ASJC Scopus subject areas

- Astronomy and Astrophysics

### Cite this

**Combined cosmological tests of a bivalent tachyonic dark energy scalar field moDel.** / Keresztes, Z.; Gergely, L.

Research output: Contribution to journal › Article

}

TY - JOUR

T1 - Combined cosmological tests of a bivalent tachyonic dark energy scalar field moDel

AU - Keresztes, Z.

AU - Gergely, L.

PY - 2014/11/1

Y1 - 2014/11/1

N2 - A recently investigated tachyonic scalar field dark energy dominated universe exhibits a bivalent future: Depending on initial parameters can run either into a De Sitter exponential expansion or into a traversable future soft singularity followed by a contraction phase. We also incluDe in the moDel (i) a tiny amount of radiation, (ii) baryonic matter (Ωbh2 = 0.022161, where the Hubble constant is fixed as h = 0.706) and (iii) cold dark matter (CDM). Out of a variety of six types of evolutions arising in a more subtle classification, we iDentify two in which in the past the scalar field effectively Degenerates into a dust (its pressure drops to an insignificantly low negative value). These are the evolutions of type IIb converging to De Sitter and type III hitting the future soft singularity. We confront these background evolutions with various cosmological tests, including the supernova type Ia Union 2.1 data, baryon acoustic oscillation distance ratios, Hubble parameter-redshift relation and the cosmic microwave background (CMB) acoustic scale. We Determine a subset of the evolutions of both types which at 1σ confiDence level are consistent with all of these cosmological tests. At perturbative level we Derive the CMB temperature power spectrum to find the best agreement with the Planck data for ΩCDM = 0.22. The fit is as good as for the ΛCDM moDel at high multipoles, but the power remains slightly overestimated at low multipoles, for both types of evolutions. The rest of the CDM is effectively generated by the tachyonic field, which in this sense acts as a combined dark energy and dark matter moDel.

AB - A recently investigated tachyonic scalar field dark energy dominated universe exhibits a bivalent future: Depending on initial parameters can run either into a De Sitter exponential expansion or into a traversable future soft singularity followed by a contraction phase. We also incluDe in the moDel (i) a tiny amount of radiation, (ii) baryonic matter (Ωbh2 = 0.022161, where the Hubble constant is fixed as h = 0.706) and (iii) cold dark matter (CDM). Out of a variety of six types of evolutions arising in a more subtle classification, we iDentify two in which in the past the scalar field effectively Degenerates into a dust (its pressure drops to an insignificantly low negative value). These are the evolutions of type IIb converging to De Sitter and type III hitting the future soft singularity. We confront these background evolutions with various cosmological tests, including the supernova type Ia Union 2.1 data, baryon acoustic oscillation distance ratios, Hubble parameter-redshift relation and the cosmic microwave background (CMB) acoustic scale. We Determine a subset of the evolutions of both types which at 1σ confiDence level are consistent with all of these cosmological tests. At perturbative level we Derive the CMB temperature power spectrum to find the best agreement with the Planck data for ΩCDM = 0.22. The fit is as good as for the ΛCDM moDel at high multipoles, but the power remains slightly overestimated at low multipoles, for both types of evolutions. The rest of the CDM is effectively generated by the tachyonic field, which in this sense acts as a combined dark energy and dark matter moDel.

KW - cosmological perturbation theory

KW - dark energy theory

UR - http://www.scopus.com/inward/record.url?scp=84914178579&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84914178579&partnerID=8YFLogxK

U2 - 10.1088/1475-7516/2014/11/026

DO - 10.1088/1475-7516/2014/11/026

M3 - Article

VL - 2014

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 11

M1 - 026

ER -