Multipole decomposition of gravitational lensing

We study gravitational lensing by a generic extended mass distribution. For that, we consider the diffraction of electromagnetic (EM) waves an extended, weakly aspherical, gravitating object. account for static field such lens representing its exterior potential in most form, expressed via infinite set symmetric trace free (STF) tensor multipole moments. This yields general form phase shift, which allows comprehensive description optical properties lens. found that at each order STF moments, shift is characterized only two parameters: magnitude and rotation angle characterize corresponding caustics, point spread function (PSF) Both these parameters are uniquely terms transverse-trace (TT) projections moments on plane. Not does this result simplify development physically consistent models realistic lenses, it also drastically reduces number required ultimate model. To help with interpretation results, established correspondence TT-projected representation spherical harmonics. axisymmetric distributions, new results those obtained previous studies. arbitrary our novel offer insight into astrophysical systems. These findings discussed context ongoing investigations as well observations planned solar (SGL).