NBIA Seminar: Rostom Mbarek

The origin of Ultra-High-Energy Cosmic Rays (UHECRs) and the highest-energy astrophysical neutrinos remains as one of the most prominent unresolved questions in astrophysics. We can shed light on such phenomena employing a thorough bottom-up approach to understand the spectra of UHECRs, neutrinos, and eventually x/gamma-rays from Active Galactic Nucleus (AGN) jets. In this respect, I will initially discuss an original theory of particle acceleration in AGN jets, i.e., the espresso mechanism, that we back by propagating protons and heavier elements in relativistic 3D MHD simulations of AGN jets accounting self-consistently for i) particle injection, ii) particle acceleration, iii) spectra of UHECRs, iv) effects of losses on UHECRs, and v) the resulting neutrino spectral features. Moving from the global scale of jets to the kinetic scales of the plasma, I will also present the first steps in understanding asymmetric reconnection in the relativistic regime using Particle-in-Cell (PIC) simulations. Considering the turbulent nature of AGNs, asymmetric reconnection can potentially be the main driver of nonthermal lepton acceleration, and thus nonthermal radiation, important to modeling UHECR losses and neutrino production. I will finally touch upon the interplay of these two regimes and potential ways of combining them.