Centre for Complexity Science seminar. Online.
Flocking — the collective motion exhibited by active matter systems capable of spontaneously breaking their rotational symmetry — is a ubiquitous phenomenon, observed in a wide array of different living systems and on an even wider range of scales. Examples range from fish schools and flocks of birds to bacteria colonies and cellular migrations down to the cooperative behaviour of molecular motors and biopolymers at the subcellular level.
In this talk we will briefly discuss the universal properties of the bulk flocking state, as described by the celebrated Toner & Tu equations. We will see that flocking is a non-equilibrium stationary state characterized by a strongly fluctuating ordered phase endowed by long-ranged, massless correlations in its slow fields (the density and orientation ones).
In the second part, we will discuss the behaviour of collective motion under
- Strong confinement, a set-up of great relevance for many experimental realizations with active colloids, where confinement by hard boundaries (e.g.: in a ring geometry is practically unavoidable.
- External driving, a problem of biological significance (group response to external threats, driven cellular migration, etc.) which could also pave the way for the control flocking systems, either biological or artificial.