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| Paper IPM / P / 17663 | ||||||||||||||||||||||||||||
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Hubble tension is a problem in one-dimensional (1D) posteriors, since local H0 determinations are only sensitive to a single parameter. Projected 1D posteriors for ΛCDM 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 χ2 minimum at 68% confidence level in high redshift bins.
To remedy this limitation of MCMC, we resort to profile distributions as a complementary technique. Doing so, we observe that z≳ cosmic chronometer (CC) data currently prefers a non-evolving (constant) Hubble parameter over a Planck-\LambdaCDM cosmology at \sim 2 \sigma. 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 \chi^2. Finally, on the assumption that the Planck-\LambdaCDM cosmological model is correct, using profile distributions we confirm a >2 \sigma discrepancy with Planck-\LambdaCDM 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.
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