Doubling Strong Lensing as a Cosmological Probe

TL;DR

This paper explores the use of double source plane gravitational lens systems as a novel and highly sensitive method for constraining dark energy properties, demonstrating significant improvements in cosmological parameter estimation.

Contribution

It introduces the double source distance ratio as a new cosmological probe and shows its strong complementarity and enhanced sensitivity to dark energy parameters compared to traditional methods.

Findings

Double source distance ratio is more sensitive to dark energy parameters than matter density.

Adding these measurements can improve dark energy constraints by 40%.

Optimal redshift distribution enhances the probe's effectiveness.

Abstract

Strong gravitational lensing provides a geometric probe of cosmology in a unique manner through distance ratios involving the source and lens. This is well known for the time delay distance derived from measured delays between lightcurves of the images of variable sources such as quasars. Recently, double source plane lens systems involving two constant sources lensed by the same foreground lens have been proposed as another probe, involving a different ratio of distances measured from the image positions and fairly insensitive to the lens modeling. Here we demonstrate that these two different sets of strong lensing distance ratios have strong complementarity in cosmological leverage. Unlike other probes, the double source distance ratio is actually more sensitive to the dark energy equation of state parameters $w_0$ and $w_a$ than to the matter density $\Omega_m$, for low redshift lenses. Adding double source distance ratio measurements can improve the dark energy figure of merit by 40% for a sample of fewer than 100 low redshift systems, or even better for the optimal redshift distribution we derive.