Accurate Weak Lensing of Standard Candles. II. Measuring sigma8 with Supernovae

TL;DR

This paper proposes a novel method to measure the cosmological parameter sigma8 using the non-Gaussian features in supernova brightness caused by weak lensing, achieving competitive precision with large SN datasets.

Contribution

It introduces a new approach that leverages weak lensing effects on supernova brightness to constrain sigma8 without relying on prior knowledge of intrinsic dispersion.

Findings

Predicts 7% sigma8 constraint with 100,000 SNe

Achieves 3% sigma8 constraint with 500,000 SNe

Method is independent and complementary to existing cosmological probes

Abstract

Soon the number of type Ia supernova (SN) measurements should exceed 100,000. Understanding the effect of weak lensing by matter structures on the supernova brightness will then be more important than ever. Although SN lensing is usually seen as a source of systematic noise, we will show that it can be in fact turned into signal. More precisely, the non-Gaussianity introduced by lensing in the SN Hubble diagram dispersion depends rather sensitively on the amplitude sigma8 of the matter power spectrum. By exploiting this relation, we are able to predict constraints on sigma8 of 7% (3%) for a catalog of 100,000 (500,000) SNe of average magnitude error 0.12 without having to assume that such intrinsic dispersion is known a priori. The intrinsic dispersion has been assumed to be Gaussian; possible intrinsic non-Gaussianities in the dataset (due to the SN themselves and/or to other transients) could be potentially dealt with by means of additional nuisance parameters describing higher moments of the intrinsic dispersion distribution function. This method is independent of and complementary to the standard methods based on CMB, cosmic shear or cluster abundance observables.