Xihui Zhao

From the calendar

Cosmic rays (CRs) play a pivotal role in variousastrophysical systems, delivering feedback that spans a broad rangeof scales. However, modeling their transport remains challenging due to theinherent multi-scale nature and microphysical complexities. Recent advancementsin two-moment CR hydrodynamics have alleviated some of these challengesand deepened our understanding of CR feedback. Yet, current two-moment methodsmay not fully incorporate all possible CR transport processes,while the outcome of CR feedback sensitively depends on these underlyingmicrophysics. Furthermore, numerical challenges persist, includinginstabilities from stiff streaming terms and ambiguities in solver design forcoupled CR-MHD systems. We develop a two-moment description for CRhydrodynamics from first principles, and implement our formulation as a new CRfluid module to the ATHENA++ code. To test the code, we investigate thecharacteristic CR-MHD waves in such systems as benchmarks, and provide adetailed analysis of their properties. In this talk, I will introduce ourformulations, and show the improved performance of our module. I will alsoshare our preliminary findings of the CR-MHD waves.