Cosmic expansion history from SNe Ia data via information field theory: the charm code

摘要

We present charm (cosmic history agnostic reconstruction method), a novel inference algorithm that reconstructs the cosmic expansion history as encoded in the Hubble parameter H ( z ) from SNe Ia data. The novelty of the approach lies in the usage of information field theory, a statistical field theory that is very well suited for the construction of optimal signal recovery algorithms. The charm algorithm infers non-parametrically s ( a ) = ln( ρ ( a ) / ρ _(crit0)) , the density evolution which determines H ( z ) , without assuming an analytical form of ρ ( a ) but only its smoothness with the scale factor a = (1 + z )~(-1) . The inference problem of recovering the signal s ( a ) from the data is formulated in a fully Bayesian way. In detail, we have rewritten the signal as the sum of a background cosmology and a perturbation. This allows us to determine the maximum a posteriory estimate of the signal by an iterative Wiener filter method. Applying charm to the Union2.1 supernova compilation, we have recovered a cosmic expansion history that is fully compatible with the standard Λ CDM cosmological expansion history with parameter values consistent with the results of the Planck mission.