报告题目：Boundary and bulk perturbation in vectorial active matter
报告人：Giuseppe Fava 博士，意大利University of Insubria
报告时间：2025年5月21日（周三 ）下午3:00
报告地点：物理科技楼409室
报告摘要：Active matter, i.e., nonequilibrium systems capable of transforming some non-thermal energy present in the environment into self-propulsion or other functional mechanisms, has attracted the attention of the statistical physics community in the past decades. Flocking is perhaps one of the most intriguing examples of collective behaviors exhibited by active matter systems, as shown by the aerial displays of starling flocks.
While our knowledge of the bulk behavior of free collective motion, i.e., flocking, is now fairly complete, at least when the surrounding fluid may be safely neglected (the so-called dry approximation) much less is known when collective motion is achieved explicitly breaking a continuous rotational symmetry, either at the global or local level. Symmetry breaking at the global level can perhaps be due to an anisotropic environment, where a favored direction determines the mean flocking direction. A key question is how it is possible to detect the presence of small anisotropies in the system without prior knowledge of the underlying environmental asymmetry.
On the other hand, in confined flocking systems, local anisotropies can arise at the boundaries, which significantly affect both the bulk and boundary behavior of the system, especially in finite-sized setups. I will focus in particular on the effects induced by confining a polar active fluid between two parallel and repelling walls, showing how the effect of the boundaries extends far into the bulk of the system.
Finally, I will consider a more subtle confinement, inspired by the phototactic behavior of certain cyanobacteria, showing how some key features of active matter, such as accumulation at boundaries,are possible also in the absence of mechanical confinement.
References
1. Fava, G., Gambassi,A., & Ginelli,F. (2024). Strong Casimir-like forces in flocking active matter. PRL, 133(14), 148301;
2. Lenzini, L., Fava, G.,& Ginelli,F. (2024). Boundary symmetry breaking of flocking systems. JSTAT, 2024(8), 083210;
3. Brambati, M., Fava, G., & Ginelli, F. (2022). Signatures of directed and spontaneous flocking. PRE, 106(2), 024608;
4. Fava,G., Ginelli,F.,Mahault,B., in preparation.
