Nonlinear Guiding Center Theory of Perpendicular Diffusion: Derivation from the Newton‐Lorentz Equation

We revisit the problem of charged-particle scattering in the direction perpendicular to a mean magnetic field. By combining the well-established nonlinear guiding center theory with the Newton-Lorentz equation, we derive an integral equation for perpendicular scattering without the assumption that charged particles follow magnetic field lines. A comparison with solar wind observations is also presented.