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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Present-day coasting in a flat FLRW cosmology with a transient acceleration pocket

  • Lilia Ferrario1
  1. 1Mathematical Sciences Institute, The Australian National University , Canberra, ACT 2601 ,
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Abstract

We revisit whether cosmological data require present-day acceleration. We introduce a compact phenomenological parametrization for the equation of state of a separately conserved smooth component, with independently adjustable low- and high-redshift limits and a localized pressure feature of variable location, width, and amplitude. This provides a flexible alternative to CPL-like forms, allowing intermediate-redshift structure in the expansion history to be modelled without tying it rigidly to the high-redshift limit. Embedding this component in a flat Friedmann–Lemaître–Robertson–Walker (FLRW) model with pressureless matter, we test exact present-day coasting and a corresponding free-q0 extension. We fit DESI DR2 BAO, the Planck CMB distance prior, Pantheon + SH0ES Type Ia supernovae, and fσ 8, using both the original SN sample and the progenitor-age-corrected form proposed by Son et al. (2025). We find that exact coasting provides a competitive fit once the Son et al. correction is applied and freeing q0 gives only a marginal improvement, so present-day acceleration is not required by this combined data set.

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Cite

BibTeXRIS
BibTeX
@article{ferrario2026presentday,
  title = {{Present-day coasting in a flat FLRW cosmology with a transient acceleration pocket}},
  author = {Lilia Ferrario},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag1858},
  url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1858/9002813},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Present-day coasting in a flat FLRW cosmology with a transient acceleration pocket
AU  - Lilia Ferrario
PY  - 2026
DA  - 2026/10/27
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1858
UR  - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1858/9002813
AB  - We revisit whether cosmological data require present-day acceleration. We introduce a compact phenomenological parametrization for the equation of state of a separately conserved smooth component, with independently adjustable low- and high-redshift limits and a localized pressure feature of variable location, width, and amplitude. This provides a flexible alternative to CPL-like forms, allowing intermediate-redshift structure in the expansion history to be modelled without tying it rigidly to the high-redshift limit. Embedding this component in a flat Friedmann–Lemaître–Robertson–Walker (FLRW) model with pressureless matter, we test exact present-day coasting and a corresponding free-q_0 extension. We fit DESI DR2 BAO, the Planck CMB distance prior, Pantheon + SH0ES Type Ia supernovae, and fσ _8, using both the original SN sample and the progenitor-age-corrected form proposed by Son et al. (2025). We find that exact coasting provides a competitive fit once the Son et al. correction is applied and freeing q_0 gives only a marginal improvement, so present-day acceleration is not required by this combined data set.
SN  - 1365-2966
SN  - 0035-8711
ER  -