  Structure formation shocks are believed to be the largest accelerators of
cosmic rays in the Universe. However, little is still known about their
efficiency in accelerating relativistic electrons and protons as a function of
their magnetization properties, i.e. of their magnetic field strength and
topology. In this work, we analyzed both uniform and adaptive mesh resolution
simulations of large-scale structures with the magnetohydrodynamical grid code
Enzo, studying the dependence of shock obliquity with different realistic
scenarios of cosmic magnetism. We found that shock obliquities are more often
perpendicular than what would be expected from a random three-dimensional
distribution of vectors, and that this effect is particularly prominent in the
proximity of filaments, due to the action of local shear motions. By coupling
these results to recent works from particle-in-cell simulations, we estimated
the flux of cosmic-ray protons in galaxy clusters, and showed that in principle
the riddle of the missed detection of hadronic gamma-ray emission by the
Fermi-LAT can be explained if only quasi-parallel shocks accelerate protons. On
the other hand, for most of the cosmic web the acceleration of cosmic-ray
electrons is still allowed, due to the abundance of quasi-perpendicular shocks.
We discuss quantitative differences between the analyzed models of
magnetization of cosmic structures, which become more significant at low cosmic
overdensities.
