Ion injection at quasi-perpendicular shocks
In plain words
Simulations show ions are efficiently accelerated when the magnetic field is roughly along the shock's direction of travel, but hardly at all when it is across it. Real shocks have every orientation, so whether across-field shocks can inject ions matters for cosmic-ray yields.
Precise statement
Hybrid simulations find ion acceleration efficiency of order 10 percent of the shock kinetic energy flux for $\theta_{\mathrm{Bn}}$ below about $45\,\mathrm{degrees}$ and strong suppression at larger angles. Determine whether upstream turbulence, shock-surface rippling or pre-existing energetic seeds allow efficient ion injection at $\theta_{\mathrm{Bn}}$ above $50\,\mathrm{degrees}$, and the resulting efficiency versus $M_{\mathrm{A}}$. An answer is $\operatorname{efficiency}(\theta_{\mathrm{Bn}}, M_{\mathrm{A}})$ from 3D hybrid or kinetic simulations with realistic upstream turbulence.
What would settle it
3D simulations with realistic upstream turbulence, checked against spacecraft observations of quasi-perpendicular interplanetary shocks.