Abstract

Galaxies align towards each other in a way that is correlated with the large-scale structure of the Universe. These intrinsic alignments are a known contaminant to weak gravitational lensing and clustering cosmology. In the first half of the talk, we will give an overview of intrinsic alignments. We will discuss what we know about them from an observational perspective and how they contaminate weak lensing and clustering measurements. We will also point out some of their cosmological applications. In the second half, we will present some perturbative models that have been employed in the literature to describe intrinsic alignments, along with some recent developments in this direction. In particular, the recently developed Effective Field Theory of Intrinsic Alignments generalises other perturbative models and is able to describe B-modes of halo intrinsic alignments with high precision on quasi-linear scales. We also briefly discuss a hybrid Lagrangian approach which blends simulation-based methods and perturbation theory in order to improve the model fit on even smaller scales, which is particularly relevant for weak lensing mitigation.