How do changes in the spatial and temporal correlations arising from activity affect the glass transition?

Assemblies of active colloidal particles serve as model systems for the heterogeneous, collective dynamics of self-propelled, living materials, such as flocking in bacterial films and correlated cell motion during wound healing and embryogenesis. Despite recent advances, the effects of activity on the glassy dynamics of dense active matter are still largely debated. Using numerical simulations of active brownian particles, we study how activity affects the dynamical slow-down near the glass transition as a function of the temperature of the thermal bath, particle packing fraction, and Peclet number. We focus on measurements of the spatial and temporal Fourier transforms of the kinetic K(q,omega) and potential U(q,omega) energies of the system. We take a stepwise approach, first measuring K(q,omega) and U(q,omega) in systems at constant energy, then in the presence of a Langevin thermostat near the glass transition, and finally with active forces with a given strength and persistence time. We find that the active forces can either enhance or disrupt the two step-relaxation of glass-forming liquids, and connect this behavior to changes in the spatial and temporal correlations of the system. This work offers fundamental insights into the differences between the glassy dynamics that occurs in thermal energy-driven versus activity-driven systems, an important step forward in modeling active motion in living and non-living materials.