Markov chain Monte Carlo analysis of Bianchi VII_h models

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dc.creatorBridges, M.
dc.creatorMcEwen, J. D.
dc.creatorLasenby, A. N.
dc.creatorHobson, M. P.
dc.date2006-05-12
dc.date2007-09-17
dc.date.accessioned2026-07-07T11:04:02Z
dc.date.available2026-07-07T11:04:02Z
dc.descriptionWe have extended the analysis of Jaffe et al. to a complete Markov chain Monte Carlo (MCMC) study of the Bianchi type ${\rm VII_h}$ models including a dark energy density, using 1-year and 3-year Wilkinson Microwave Anisotropy Probe (WMAP) cosmic microwave background (CMB) data. Since we perform the analysis in a Bayesian framework our entire inference is contained in the multidimensional posterior distribution from which we can extract marginalised parameter constraints and the comparative Bayesian evidence. Treating the left-handed Bianchi CMB anisotropy as a template centred upon the `cold-spot' in the southern hemisphere, the parameter estimates derived for the total energy density, `tightness' and vorticity from 3-year data are found to be: $Ω_{tot} = 0.43\pm 0.04$, $h = 0.32^{+0.02}_{-0.13}$, $ω= 9.7^{+1.6}_{-1.5}\times 10^{-10}$ with orientation $γ= {337^{\circ}}^{+17}_{-23}$). This template is preferred by a factor of roughly unity in log-evidence over a concordance cosmology alone. A Bianchi type template is supported by the data only if its position on the sky is heavily restricted. The low total energy density of the preferred template, implies a geometry that is incompatible with cosmologies inferred from recent CMB observations. Jaffe et al. found that extending the Bianchi model to include a term in $Ω_Λ$ creates a degeneracy in the $Ω_m - Ω_Λ$ plane. We explore this region fully by MCMC and find that the degenerate likelihood contours do not intersect areas of parameter space that 1 or 3 year WMAP data would prefer at any significance above $2σ$. Thus we can confirm that a physical Bianchi ${\rm VII_h}$ model is not responsible for this signature.
dc.description8 pages, 10 figures, significant update to include more accurate results and conclusions to match version accepted by MNRAS
dc.identifierhttps://arxiv.org/abs/astro-ph/0605325
dc.identifierhttp://arxiv.org/abs/astro-ph/0605325
dc.identifierMon.Not.Roy.Astron.Soc.377:1473-1480,2007
dc.identifierdoi:10.1111/j.1365-2966.2007.11616.x
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/188752
dc.subjectAstrophysics
dc.titleMarkov chain Monte Carlo analysis of Bianchi VII_h models
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