https://doi.org/10.1140/epjc/s10052-024-13727-0
Regular Article - Theoretical Physics
A comparison of Bayesian and frequentist confidence intervals in the presence of a late Universe degeneracy
1
Atlantic Technological University, Ash Lane, Sligo, Ireland
2
School of Physics, Institute for Research in Fundamental Sciences (IPM), P.O.Box 19395-5531, Tehran, Iran
3
The Abdus Salam ICTP, Strada Costiera 11, 34014, Trieste, Italy
4
Department of Physics, Bu-Ali Sina University, 65178, Hamedan, Iran
Received:
6
August
2024
Accepted:
15
December
2024
Published online:
1
February
2025
Hubble tension is a problem in one-dimensional (1D) posteriors, since local 
determinations are only sensitive to a single parameter. Projected 1D posteriors for 
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 
minimum at 
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 
cosmic chronometer (CC) data currently prefer a non-evolving (constant) Hubble parameter over a Planck-CDM cosmology at 
. Within the Hubble tension debate, it is imperative that subsamples of data sets with differing redshifts yield similar values. In addition, we confirm that MCMC degeneracies observed in 2D posteriors are not due to curves of constant . Finally, on the assumption that the Planck-CDM cosmological model is correct, using profile likelihoods we confirm a 
discrepancy with Planck-CDM in a combination of CC and baryon acoustic oscillations (BAO) data beyond 
. This confirms a discrepancy reported earlier with fresh methodology.
© The Author(s) 2025
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