Non-parametric Cosmology with Cosmic Shear

TL;DR

This paper introduces a non-parametric method to measure the Universe's structure growth and geometry using cosmic shear data, avoiding assumptions about the cosmological model, and tests it on CFHTLenS data.

Contribution

It develops a novel non-parametric approach to simultaneously reconstruct key cosmological functions from shear data, enabling model-independent tests of LCDM.

Findings

Lensing constrains a single global power spectrum amplitude.

Reconstructed co-moving distance r(z) is higher than LCDM prediction below z=0.4.

Reconstruction results are consistent with LCDM at higher redshifts.

Abstract

We present a method to measure the growth of structure and the background geometry of the Universe -- with no a priori assumption about the underlying cosmological model. Using Canada-France-Hawaii Lensing Survey (CFHTLenS) shear data we simultaneously reconstruct the lensing amplitude, the linear intrinsic alignment amplitude, the redshift evolving matter power spectrum, P(k,z), and the co-moving distance, r(z). We find that lensing predominately constrains a single global power spectrum amplitude and several co-moving distance bins. Our approach can localise precise scales and redshifts where Lambda-Cold Dark Matter (LCDM) fails -- if any. We find that below z = 0.4, the measured co-moving distance r (z) is higher than that expected from the Planck LCDM cosmology by ~1.5 sigma, while at higher redshifts, our reconstruction is fully consistent. To validate our reconstruction, we compare LCDM parameter constraints from the standard cosmic shear likelihood analysis to those found by fitting to the non-parametric information and we find good agreement.