= Quasilinear diffusion in action space
The second-order, angle-averaged evolution of a <galactic distribution function> caused by weak fluctuating gravitational perturbations. In <action-angle variables>, the first-order response to a <Fourier series> harmonic feeds a second-order flux proportional to $\mathbf k(\mathbf k\cdot\partial_{\mathbf J}f_0)$ and to the perturbation's power. Orbital <resonances> select where transport is strongest; a finite pulse produces <Gaussian resonance broadening> when its time envelope is a <Gaussian function>. The general flux retains time memory until a further short-memory or pulse-integrated approximation is made.
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