Description
In this talk I will review the concept of the line-of-sight (LOS) shear, a model for external shear in strong lensing that is theoretically free from degeneracies with lens model parameters. Measurements of the LOS shear will provide new, independent constraints on cosmological parameters such as $\sigma_8$ via a cross-correlation with traditional weak lensing probes. I will present a mock-based proof-of-concept that this observable is measurable from strong lenses, along with the first measurements of LOS shear from the SLACS strong lens sample. I will further show estimates for the expected cosmological signal of LOS shear measured in Euclid, and a forecast for constraints achievable on $\sigma_8$ from the full Euclid Wide Survey.
Based on 2210.07210, 2405.12091, 2501.16292 and work in prep.
