Microphysics of Cosmic Ray Production: Bridging Plasma Theory and Multi-Messenger Observations

by Dr Siddhartha Gupta (Princeton University)

Monday 30 Mar 2026, 14:30 → 16:30 Asia/Kolkata

AG 66 (TIFR, Mumbai)

: We are living in an exciting era of space and astrophysical research, where multi-messenger approaches—using cosmic rays, electromagnetic radiation, gravitational waves, and neutrinos—are reshaping our view of the universe. Cosmic rays, high-energy charged nonthermal particles, play a central role in this research. While the primary mechanism of cosmic ray acceleration, known as diffusive shock acceleration, is well established, two fundamental mysteries remain in high-energy astrophysics: the "injection problem," or how thermal particles first enter the nonthermal pool, and how these particles self-consistently accelerate to high energies. Understanding these processes is crucial, as nonthermal particles produce radio, X-ray, and gamma-ray emission and exert dynamical pressure that can reshape their acceleration sites. This has important implications for space and astrophysical plasmas, ground-based nonthermal particle (including neutrino and muon) detectors, and laboratory plasma experiments. I will show how ab-initio kinetic plasma theory and simulations of astrophysical shocks, combined with magnetohydrodynamic models, unravel these processes. This research is essential for developing subgrid models and interpreting the phenomenology of nonthermal sources across diverse environments, from the solar system to supernova remnants, galaxies, and galaxy clusters. I will conclude by highlighting that current multi-messenger observations demand more accurate theories, which require bridging fundamental plasma physics and large-scale astrophysical phenomena.