Rheology of athermal amorphous solids: Revisiting simplified scenarios and the concept of mechanical noise temperature
We study the rheology of amorphous solids in the limit of negligible thermal fluctuations. General arguments indicate that the shear-rate dependence of the stress results from an interplay between the time scales of the macroscopic drive and the (cascades of) local particle rearrangements. Such rearrangements are known to induce a redistribution of the elastic stress in the system. Although mechanical noise, i.e., the local stress fluctuations arising from this redistribution, is widely believed to activate new particle rearrangements, we provide evidence that it casts severe doubt on the analogy with thermal fluctuations: mechanical and thermal fluctuations lead to asymptotically different statistics for barrier crossing. These ideas are illustrated and supported by a simple elasto-plastic model whose ingredients are directly connected with the physical processes relevant for the flow.