Structural features and dynamical predictions in dense active packings

Amorphous solids and dense active materials are characterized by structural disorder, nontrivial mechanical properties, and interesting dynamics. In existing work that focuses on athermal disordered solids under shear, metrics derived from linear response theory forecast structural instabilities and plastic rearrangement using information from a single snapshot of a configuration. However, no such formulation of these metrics exists for systems with active forces or structural gradients. In the context of dense crowd dynamics, the linear response of active particulate systems has been approximated using positional fluctuations. While seminal, these methods have serious limitations in predictivity, as they require large amounts of time-resolved data. To address these shortcomings, we developed a novel theoretical and computational framework to study a class of packings formed by persistent self-propelled particles. Using a mapping between self-propulsion and an external potential, we test predictions of structural metrics in distinct regions of the system. Applications of this work could be instrumental in preventing dangerous emergent phenomena in dense human crowds and studying the stability of materials with structural gradients.