2006/08/31 by Roberto Trotta · 3 citations
Mathematics · Physics and Astronomy · #Adiabatic process #Anisotropy #Astrophysics #Bayes factor #Bayesian inference #Bayesian probability #CMB cold spot #Cosmic microwave background #Cosmology and Gravitation Theories #Fraction (chemistry) #Galaxies: Formation, Evolution, Phenomena #Mathematics #Model selection #Neutrino #Particle physics #Particle physics theoretical and experimental studies #Physics #Quantum mechanics #Statistical physics #Statistics #Superposition principle #astro-ph
paper · pdf · doi:10.1111/j.1745-3933.2006.00268.x
published as Mon.Not.Roy.Astron.Soc.375:L26-L30,2007 · Expanded discussion of degeneracies, updated references, no change to conclusions. Matches published version
openalex publication_date 2006/12/21 · arxiv created 2007/03/02 · arxiv updated 2014/10/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Abstract I revisit the question of the adiabaticity of initial conditions for cosmological perturbations in view of the 3-yr Wilkinson Microwave Anisotropy Probe (WMAP) data. I focus on the simplest alternative to purely adiabatic conditions, namely a superposition of the adiabatic mode and one of the three possible isocurvature modes, with the same spectral index as the adiabatic component. I discuss findings in terms of posterior bounds on the isocurvature fraction and Bayesian model selection. The Bayes factor (models likelihood ratio) and the effective Bayesian complexity are computed for several prior ranges for the isocurvature content. I find that the cold dark matter isocurvature fraction is now constrained to be less than about 10 per cent, while the fraction in either the neutrino entropy or velocity mode is below about 20 per cent. Model comparison strongly disfavours mixed models that allow for isocurvature fractions larger than unity, while current data do not allow one to distinguish between a purely adiabatic model and models with a moderate (i.e. below about 10 per cent) isocurvature contribution. The conclusion is that purely adiabatic conditions are strongly favoured from a model selection perspective. This is expected to apply in even stronger terms to more complicated superpositions of isocurvature contributions.