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Abstract Cosmic rays (CRs) interact with turbulent magnetic fields in the interstellar medium (ISM), generating nonthermal emission. After many decades of studies, the theoretical understanding of their diffusion in the ISM continues to pose a challenge. This study numerically explores a recent prediction termed “mirror diffusion” and its synergy with the traditional diffusion mechanism based on gyroresonant scattering. Our study combines 3D MHD simulations of star-forming regions with test particle simulations to analyze CR diffusion. We demonstrate the significance of mirror diffusion in CR diffusion parallel to the magnetic field when the mirroring condition is satisfied. Our results support the theoretical expectation that the resulting particle propagation arising from mirror diffusion in combination with much faster diffusion induced by gyroresonant scattering resembles a Levy-flight-like propagation. Our study highlights the necessity to reevaluate the diffusion coefficients traditionally adopted in the ISM based on gyroresonant scattering alone. For instance, our simulations imply a diffusion coefficient ∼10²⁷cm²s^–1for particles with a few hundred TeV within regions spanning a few parsecs around the source. This estimate is in agreement with gamma-ray observations, which show the relevance of our results for the understanding of gamma-ray emission in star-forming regions. 

Abstract We investigate the impact of turbulence on magnetic reconnection through high-resolution 3D magnetohydrodynamic (MHD) simulations, spanning Lundquist numbers fromS= 10³to 10⁶. Building on the A. Lazarian & E. T. Vishniac theory, which asserts reconnection rate independence from ohmic resistivity, we introduce small-scale perturbations untilt= 0.1t_A. Even after the perturbations cease, turbulence persists, resulting in sustained high reconnection rates ofV_rec/V_A∼ 0.03–0.08. These rates exceed those generated by resistive tearing modes (plasmoid chain) in 2D and 3D MHD simulations by factors of 5–6. Our findings match observations in solar phenomena and previous 3D MHD global simulations of solar flares, accretion flows, and relativistic jets. The simulations show a steady-state fast reconnection rate compatible with the full development of turbulence in the system, demonstrating the robustness of the process in turbulent environments. We confirm reconnection rate independence from the Lundquist number, supporting Lazarian and Vishniac’s theory of fast turbulent reconnection. Additionally, we find a mild dependence ofV_recon the plasma–βparameter, decreasing from 0.036 to 0.028 (in Alfvén units) asβincreases from 2.0 to 64.0 for simulations with a Lundquist number of 10⁵. Lastly, we explore the magnetic Prandtl number’s (Pr_m=ν/η) influence on the reconnection rate and find it negligible during the turbulent regime across the range tested, from Pr_m= 1 to 60.