Turning noise into signal: learning from the scatter in the Hubble diagram

TL;DR

This paper demonstrates how combining peculiar velocity and weak-lensing analyses of supernova data can extract valuable information about the matter power spectrum and growth history, providing constraints that complement other cosmological measurements.

Contribution

It introduces a method to simultaneously analyze peculiar velocity and lensing effects in supernova data to constrain cosmological parameters with improved precision.

Findings

Constraints on σ8 and γ from supernova data.

Orthogonal degeneracies between velocity and lensing effects.

Potential for improved constraints with more supernovae.

Abstract

The supernova (SN) Hubble diagram residual contains valuable information on both the present matter power spectrum and its growth history. In this paper we show that this information can be retrieved with precision by combining both peculiar velocity and weak-lensing analysis on the data. To wit, peculiar velocity induces correlations on the nearby SN while lensing induces a non-Gaussian dispersion in faraway objects. We show that both effects have almost orthogonal degeneracies and discuss how they can be extracted simultaneously from the data. We analyze the JLA supernova catalog in a 14-dimensional parameter space, assuming a flexible growth-rate index $\gamma$. We arrive at the following marginalized constraints: $\sigma_8 = 0.65^{+0.23}_{-0.37}$ and $\gamma = 1.38^{+1.7}_{-0.65}$. Assuming instead GR as the correct gravitation theory (and thus $\gamma \equiv 0.55$), the constraints in $\sigma_8$ tighten further: $\sigma_8 = 0.40^{+0.21}_{-0.23}$. We show that these constraints complement well the ones obtained from other datasets and that they could improve substantially with more SNe.