The Role of Jet–Cocoon Mixing, Magnetization, and Shock Breakout in Neutrino and Cosmic-Ray Emission from Short Gamma-Ray Bursts

We perform GRMHD and RMHD simulations of weakly highly magnetized gamma-ray burst (GRB) jets propagating in binary neutron star (BNS) merger ejecta. Using the simulations, we first find that mixing between jet cocoon, which is present all types jets, inhibits formation subphotospheric collisionless shocks. However, show a mild magnetization may lead to subshocks allow efficient proton acceleration. consider shear acceleration diffusive shock at collimation shocks, internal breakout, external provide self-consistent estimate for neutrino cosmic-ray (CR) signals from GRBs BNS mergers. short do not produce detectable with current-day facilities. Shock breakout yields $ \sim 10 PeV neutrinos viewing angles $\sim20^\circ $, independent magnetization. signal well below detection limits current detectors. Such would coincident neutrino-$\gamma-$ray detection, providing testable prediction as production site. numerical modeling fits GW170817 afterglow emission, blast waves mergers can account 5%-10% Galactic CR luminosity PeV-EeV energy range. Based on these estimates, observed level anisotropy places constraint distance latest $\lesssim3$ kiloparsecs.