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| Main Authors: | , , , |
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| Format: | Preprint |
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2023
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| Online Access: | https://arxiv.org/abs/2307.16349 |
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| _version_ | 1866917882992001024 |
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| author | Colgáin, Eoin Ó Pourojaghi, Saeed Sheikh-Jabbari, M. M. Sherwin, Darragh |
| author_facet | Colgáin, Eoin Ó Pourojaghi, Saeed Sheikh-Jabbari, M. M. Sherwin, Darragh |
| contents | Hubble tension is a problem in one-dimensional (1D) posteriors, since local $H_0$ determinations are only sensitive to a single parameter. Projected 1D posteriors for $Λ$CDM cosmological parameters become more non-Gaussian with increasing effective redshift when the model is fitted to redshift-binned data in the late Universe. We explain mathematically why this non-Gaussianity arises and show using observational Hubble data (OHD) that Markov Chain Monte Carlo (MCMC) marginalisation leads to 1D posteriors that fail to track the $χ^2$ minimum at $68\%$ confidence level in high redshift bins. To gain a second perspective, we resort to profile likelihoods as a complementary technique. Doing so, we observe that $z \gtrsim 1$ cosmic chronometer (CC) data currently prefers a non-evolving (constant) Hubble parameter over a Planck-$Λ$CDM cosmology at $\sim 2 σ$. Within the Hubble tension debate, it is imperative that subsamples of data sets with differing redshifts yield similar $H_0$ values. In addition, we confirm that MCMC degeneracies observed in 2D posteriors are not due to curves of constant $χ^2$. Finally, on the assumption that the Planck-$Λ$CDM cosmological model is correct, using profile likelihoods we confirm a $>2 σ$ discrepancy with Planck-$Λ$CDM in a combination of CC and baryon acoustic oscillations (BAO) data beyond $ z \sim 1.5$. This confirms a discrepancy reported earlier with fresh methodology. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2307_16349 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | A comparison of Bayesian and frequentist confidence intervals in the presence of a late Universe degeneracy Colgáin, Eoin Ó Pourojaghi, Saeed Sheikh-Jabbari, M. M. Sherwin, Darragh Cosmology and Nongalactic Astrophysics Hubble tension is a problem in one-dimensional (1D) posteriors, since local $H_0$ determinations are only sensitive to a single parameter. Projected 1D posteriors for $Λ$CDM cosmological parameters become more non-Gaussian with increasing effective redshift when the model is fitted to redshift-binned data in the late Universe. We explain mathematically why this non-Gaussianity arises and show using observational Hubble data (OHD) that Markov Chain Monte Carlo (MCMC) marginalisation leads to 1D posteriors that fail to track the $χ^2$ minimum at $68\%$ confidence level in high redshift bins. To gain a second perspective, we resort to profile likelihoods as a complementary technique. Doing so, we observe that $z \gtrsim 1$ cosmic chronometer (CC) data currently prefers a non-evolving (constant) Hubble parameter over a Planck-$Λ$CDM cosmology at $\sim 2 σ$. Within the Hubble tension debate, it is imperative that subsamples of data sets with differing redshifts yield similar $H_0$ values. In addition, we confirm that MCMC degeneracies observed in 2D posteriors are not due to curves of constant $χ^2$. Finally, on the assumption that the Planck-$Λ$CDM cosmological model is correct, using profile likelihoods we confirm a $>2 σ$ discrepancy with Planck-$Λ$CDM in a combination of CC and baryon acoustic oscillations (BAO) data beyond $ z \sim 1.5$. This confirms a discrepancy reported earlier with fresh methodology. |
| title | A comparison of Bayesian and frequentist confidence intervals in the presence of a late Universe degeneracy |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2307.16349 |