Title:  Pattern Formation and Elastodynamics in Active Matter

Abstract:  Active matter, referred to complex systems with self-sustaining energy sources or self-propulsive forces, has been of tremendous research interest in recent years. These active systems (e.g., humans, birds, bacteria, protein or colloidal motors, granular rotors, …) are intrinsically out of equilibrium, involving multiple spatial and temporal scales and exhibiting a vast variety of intriguing properties that are absent in conventional passive systems. In this talk I will introduce two of these aspects examined in our recent theoretical and computational studies, i.e., the competition between chiral particle self-propulsion and self-spinning, and effects of nonreciprocity when Newton’s 3rd law is not obeyed (the latter can be connected to non-Hermitian systems and phase transitions involving exceptional points and PT symmetry breaking). Some of the resulting novel phenomena during the formation and dynamics of active patterns will be discussed, such as the emergence of elastic wave in 2D overdamped active crystals, persistent dynamics of topological defects in active smectics, and some exotic patterns induced by vision-cone nonreciprocal interactions of single species.