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Chaos and the Anisotropy of Cosmic Rays

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Cosmic rays (CRs) are detected on Earth with an energy-dependent anisotropy on their arrival direction. The question of the origin of cosmic rays is inextricably connected to this anisotropy. As CRs travel in the Galaxy, they can be trapped momentarily in coherent magnetic structures present in the interstellar medium, which can induce chaotic behavior in their trajectories. This process intrinsically alters their motion so that it will not be merely diffusive. In this work, we develop a new method to characterize chaotic trajectories in bound systems. This method is based on the Finite-Time Lyapunov Exponent (FTLE), which determines the degree of chaos in the particles’ trajectories. Furthermore, we model a coherent magnetic structure with time-perturbations that can be used to describe distinct magnetic systems and basic processes. Our results show that the FTLE , i.e., the level of chaos, is related to the CRs escape time from the system by a power-law relation. Additionally, this power law persists even if perturbations act on the system, pointing to the idea that this specific power law could be an essential parameter of the system. We also find that CRs can be divided into different categories according to their chaotic behavior. Moreover, these categories are distributed in specific regions in the arrival distribution maps. Therefore, this result can provide the basis for time-variability in the CR arrival direction maps.

This talk is part of the Institute of Astronomy Seminars series.

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