Magnetic reconnection as a trigger for sub-proton-scale cascade in magnetized plasma turbulence

We provide the first numerical evidences that the development of power-law energy spectra below the so-called ion break can be related to the occurrence of magnetic reconnection, regardless of the actual state of the turbulent cascade at MHD scales. This mechanism is investigated via high-resolution two-dimensional hybrid-kinetic simulations employing complementary approaches (Lagrangian vs Eulerian) and with completely different mechanisms to feed the turbulent dynamics (freely-decaying Alfv\'enic fluctuations vs continuously-driven compressible fluctuations). In both cases, the reconnection-mediated kinetic spectrum of parallel magnetic fluctuations develops a spectral slope of $-2.8$ whether or not an MHD cascade has already developed, without changes even after a successive formation of a power law at larger scales. Once a quasi-steady turbulent state is reached, the total magnetic spectrum exhibits a slope of $-5/3$ in the MHD range and of $-3$ below the ion scales. Based on this and on the analysis of the turbulent and reconnection characteristic time scales, we therefore suggest a scenario where magnetic reconnection may represent a relevant non-local transfer mechanism simultaneously at play in addition to the classical local turbulent energy transfer.