Modeling and Simulation Group Meeting

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Numerical methods in astroparticle physics: Particle diffusion and acceleration

Speaker: Sophie Aerdker, Ruhr University Bochum

Location: Warren Weaver Hall 517

Date: Thursday, December 11, 2025, 12:30 p.m.

Synopsis:

In the past years, observations of astrophysical phenomena have become more and more detailed, including various messengers, like neutrinos, photons, and cosmic rays. Each of such messengers can provide unique information about its source and explaining the detailed data is a topical challenge. In this talk, I will focus on cosmic rays, charged particles that are deflected by the ubiquitosly present turbulent magnetic fields, unlike neutrinos or photons. As a consequence they perform a random walk, e.g. in the magnetic field of their source or our Galaxy. Furthermore, cosmic rays span a huge range in energy, their energy spectrum follows almost perfectly a power-law. The acceleration processes are thought to be of stochastic nature, particles gain energy in the presence of strong turbulence or by “diffusive shock acceleration”. 

Both particle transport in space and energy have been successfully described by Fokker-Planck equations in the past. However, recent observations in the heliosphere, as well as numerical simulations of turbulent plasmas, point to "Levy flight" behavior instead of Brownian motion. I will present a new numerical framework for modeling such advanced transport and acceleration processes based on stochastic differential equations that are equivalent to (fractional) Fokker-Planck equations. I will discuss challenges, e.g. resolving the high-energy cut-offs of the accelerated spectra, and limitations in physical systems, e.g. preventing superluminal motion.