On the maximum energy of particles accelerated in astrophysical jets
Astrophysical jets moving in an external medium produce shocks where particles can be accelerated via Diffusive Shock Acceleration (DSA). The main uncertainty is the maximum energy that particles can achieve, and this has important implications for different fields in astrophysics. In particular, one of the most exciting problems is  the origin of the Ultra High Energy Cosmic Rays, and jets from Active Galactic Nuclei (AGN) have been proposed as candidates. At lower energies cosmic rays are likely galactic. With that respect, a large fraction of gamma-ray sources in the Galaxy remain unidentified, and protostellar jets are among candidates to be the hidden cosmic ray accelerators. It was very recently demonstrated that mildly relativistic shocks in the backflows in the lobes of AGN jets  can accelerate particles  up to the Hillas energy, offering a suitable environment for the acceleration of UHECRs. However, in order to account for the heavy composition of the UHECR spectrum, a jet mass loading mechanism is needed. At lower energies, acceleration of TeV particles in protostellar jets can be quenched by ion-neutral collisions, and therefore kinetic calculations are desirable in order to compute the maximum energy of particles in low velocity shocks and non-completely ionized plasmas.  
I will investigate the maximum energy that particles can achieve when they are accelerated via DSA in  mildly-relativistic and low-velocity shocks, in AGN and protostellar jets, respectively. In the former case I will consider the shocks produced by the interaction of powerful stellar winds with the jets, whereas in the latter case we will consider the  jet termination shocks. By performing unprecedented calculations with the a newly developed hybrid code, I aim to address the maximum energy and composition of the UHECR spectrum by modeling the backflows of jet/wind interactions. In addition, I aim to address if protostellar jets can accelerate TeV particles and emit gamma rays.