Cosmological lensing as a jump process

Abstract

We develop a jump-process formalism for the probability density function (PDF) of gravitational lensing fields. In the Born approximation, each lens adds a jump to the convergence $κ$ and the two components of the shear, making lensing a jump process in redshift. For independent lenses, the joint PDF of the lensing fields obeys a compensated Kolmogorov-Feller equation, which we solve in closed form in Fourier space and extend to clustered lenses using their two-point correlation function. A Fourier-Hankel inversion then yields the joint PDF of $κ$ and the shear magnitude $γ$, from which the magnification PDF follows, including its high-magnification tail, without sampling noise. We use these PDFs to train an updated version of the FLUMEN emulator, which makes likelihood-based inference from the full magnification distribution feasible across cosmologies. To motivate such analyses, we estimate that samples of $10^4$ Roman supernovae, $10^5$ Rubin supernovae, 300 Einstein Telescope standard sirens, and 12 LISA standard sirens could constrain the matter fluctuation amplitude $σ_8$ respectively to 4.8\%, 5.1\%, 8.5\%, and 19\%, with the other cosmological parameters fixed.