PhD Thesis Defense: Rostom Mbarek

10:30–11:30 am ERC 401

Rostom Mbarek "Particle Acceleration, Propagation, and Detection: A Journey from the Kinetic Structure of Plasma Physics to Particle Transport on Cosmic Scales"

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 complement these studies by propagating UHECRs in turbulent magnetic fields over large distances to examine their impact on the delay incurred during propagation. These propagation considerations have potentially similar predictive powers for galactic cosmic rays (CRs). The confinement time of galactic CRs could also be measured in a more direct manner using CR isotope ratios. In this respect, I have been heavily involved with the High Energy Light Isotope eXperiment or HELIX experiment to obtain an observationally motivated value for the confinement time of CRs in the galaxy. HELIX is a magnet spectrometer designed to make measurements of the composition of light CR isotopes. This NASA funded experiment is outfitted with a suite of modern, high-precision particle detectors designed specifically to make measurements of significant isotopic abundance ratios in the energy range ~0.2-~10~GeV/n, a range that is not accessible to any current or planned instrument.

Event Type

PhD Thesis Defenses

Jun 1