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PreprintCC BY 4.0arXiv

A Six-Parameter Teleparallel Cosmology Beyond ΛCDM: Sign-Changing Torsional Dark Energy and Implications for H0

  • Mohamed Bedair
  • Mahmoud Hashim
  • Jackson Levi Said
  • Waleed El Hanafy
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Abstract

We investigate a particular case of the extended exponential infrared f(T) teleparallel gravity, in which the geometric sector naturally produces an effective dark-energy density that evolves from negative values in the past to positive values at late times. This behaviour could be motivated by observational results providing a compelling motivation for a geometric, sign-changing dark-energy scenario within modified gravity. We demonstrate that the parameter space of the present model contains only six parameters similar to ΛCDM. A Markov Chain Monte Carlo (MCMC) analysis using Planck, DESI, and Type Ia supernova data yields a well-constrained transition redshift of ztr ≳ 1.62, accompanied by a transition in the effective equation of state to the phantom regime (w < −1) for z < ztr. Since the effective dark energy originates from modified geometric degrees of freedom, no instabilities or violations of energy conditions arise. The model naturally accounts for the H0 tension, where Planck+DESI data combination gives H0 = 72.13 ± 0.28 km s−1 Mpc−1 in a better agreement with local measurements than ΛCDM which gives H0 = 68.46 ± 0.30 km s−1 Mpc−1. However, the model is disfavored in comparison to ΛCDM in terms of the values of χ2 of the bestfit parameters. We discuss the result among other issues related to CMB-BAO tension.

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Cite

BibTeXRIS
BibTeX
@misc{bedair2026sixparameter,
  title = {{A Six-Parameter Teleparallel Cosmology Beyond $Λ$CDM: Sign-Changing Torsional Dark Energy and Implications for $H_0$}},
  author = {Mohamed Bedair and Mahmoud Hashim and Jackson Levi Said and Waleed El Hanafy},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.10560},
  eprint = {2609.10560},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.10560},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - A Six-Parameter Teleparallel Cosmology Beyond ΛCDM: Sign-Changing Torsional Dark Energy and Implications for H_0
AU  - Mohamed Bedair
AU  - Mahmoud Hashim
AU  - Jackson Levi Said
AU  - Waleed El Hanafy
PY  - 2026
DA  - 2026/09/01
PB  - arXiv
DO  - 10.48550/arxiv.2609.10560
UR  - https://arxiv.org/abs/2609.10560
AB  - We investigate a particular case of the extended exponential infrared f(T) teleparallel gravity, in which the geometric sector naturally produces an effective dark-energy density that evolves from negative values in the past to positive values at late times. This behaviour could be motivated by observational results providing a compelling motivation for a geometric, sign-changing dark-energy scenario within modified gravity. We demonstrate that the parameter space of the present model contains only six parameters similar to ΛCDM. A Markov Chain Monte Carlo (MCMC) analysis using Planck, DESI, and Type Ia supernova data yields a well-constrained transition redshift of z_tr ≳ 1.62, accompanied by a transition in the effective equation of state to the phantom regime (w < −1) for z < z_tr. Since the effective dark energy originates from modified geometric degrees of freedom, no instabilities or violations of energy conditions arise. The model naturally accounts for the H_0 tension, where Planck+DESI data combination gives H_0 = 72.13 ± 0.28 km s^−1 Mpc^−1 in a better agreement with local measurements than ΛCDM which gives H_0 = 68.46 ± 0.30 km s^−1 Mpc^−1. However, the model is disfavored in comparison to ΛCDM in terms of the values of χ^2 of the bestfit parameters. We discuss the result among other issues related to CMB-BAO tension.
ER  -