Cosmology with the line-of-sight shear of strong gravitational lenses.

Stage-IV photometric galaxy surveys will detect strong gravitational lenses. We propose using weak-lensing perturbations to these lenses, specifically their line-of-sight (LOS) shear, as a cosmological probe. This new observable allows defining novel correlation functions, promoting the standard 3x2pt method to a 6x2pt scheme. Our analysis shows that LOS shear carries detectable cosmological information with high signal-to-noise, even in pessimistic scenarios, promising for mitigating systematics in future surveys.