An analytic ray-tracing algorithm for weak lensing

We propose a new ray-tracing algorithm to measure the weak-lensing shear and convergence fields directly from N-body simulations. We calculate the deflection of the light rays lensed by the 3D mass density field or gravitational potential along the line of sight on a grid-by-grid basis, rather than using the projected 2D lens planes. Our algorithm uses simple analytic formulae instead of numerical integrations in the computation of the projected density field along the line of sight, and so is computationally efficient and straightforward to implement. This will prove valuable in the interpretation of data from the next generation of surveys that will image many thousands of square degrees of sky.