Active matter models involve particles that are able to propel by virtue of their internal energy. These particles are assumed to be indicative of natural microswimmers such as bacteria and artificial microswimmers such as Janus microspheres. A case study involving a system of self-propelling particles in the presence of competing forces of alignment and repulsion has been considered. Spatial patterns such as ring-shaped mills and hybrid mills-clusters with high spatial correlation length are detected. Dynamical analysis employing synchronisation theory and chaos detection tools indicates the formation of a weak chimera composite (a symmetry-breaking phenomenon where multiple synchronised oscillator groups coexist with desynchronised oscillators). Currently, the effect of changes in dispersity concerned with the size and activity of particles is being studied in the purview of a dry active matter system.
The origin of collective behaviour still remains debatable; however, one of the primary reasons is presumed to be the dilution of predation risk. Evasive manoeuvres in aquatic animals have been well documented, involving a multitude of pattern formations such as mill, ball, fountain, split, and more. The behavioural rules underlying such behaviour are investigated through numerical modelling of prey entities pursued by a predator entity using an underdamped agent-based model to simulate the interactions. Individual behavioural changes can lead to large-scale changes in the flock. The objective is to build a generalised model to emulate prey response to various predation scenarios and unravel the underlying physics of behavioural switching and information transfer in a group. The efficacy of the escape manoeuvre depends on the escape signal from the afflicted prey and the loss of information during transfer in the prey flock (leading to localisation of information). A subsequent addition to the model has been made in the form of strategic hunting options for the predator based on environmental cues and memory effects. Recently, the prey response to multiple asynchronous predator attacks has been looked into, leading to observations regarding excessive coordination and the non-additive effect of predation.