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Diffraction effects which are of possible importance in gravitational lensing by low-mass objects are examined. Instead of the usual approximation of geometrical optics to treat gravitational lensing, propagation of electromagnetic waves in the presence of a point mass is formulated in terms of a scalar wave equation, which has the same form as the Schroedinger equation for Coulomb scattering of particles. Diffraction phenomena, such as the intensity of the image on the optical axis (which is infinite in the approximation of geometrical optics), the lowest mass for which significant brightening occurs, and a pattern of interference fringes, appear naturally in the well-studied solutions to this equation. Aspects of gravitational lensing involving diffraction are of possible interest in searches for dark matter in the form of low-mass stars and planets.
Deguchi et al. (Fri,) studied this question.