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SUMMARY:Nucleation and Hyperuniformity in Active Phase Separation - Mike C
 ates (University of Cambridge)
DTSTART:20240611T144000Z
DTEND:20240611T153000Z
UID:TALK214699@talks.cam.ac.uk
DESCRIPTION:Activity changes the physics of phase separation qualitatively
  and quantitatively. This talk will focus on two topics where\, although b
 ig changes might be expected in principle\, it turns out that activity can
  be dealt with by modifying passive theories without fundamentally changin
 g outcomes. The first is nucleation in the phase separation of a conserved
  scalar fieldm describing e.g. the density of active particles. Here the m
 ain role of activity is to renormalize the interfacial tension in an effec
 tive free energy description for a growing spherical droplet. This descrip
 tion exploits the very high symmetry of the problem and the method is unli
 kely to generalize to more complex cases (e.g. nucleation of an active nem
 atic). The second topic is the low-wavevector behaviour of the equal time 
 correlator S(q) in systems undergoing phase separation. In the scaling lim
 it\, order-parameter conservation ensures S(q) vanishes at low q -- which 
 is the definition of hyperuniformity. However it has long been known to va
 nish as the fourth rather than second power of q in passive phase separati
 on\, a result recently found numerically for active models as well. One lo
 ngstanding (but somewhat delicate) explanation of the passive result invok
 es a second\, hidden\, conservation law. We show that this conservation la
 w remains intact when activity is added at lowest order\, and discuss how 
 violations arising from noise and from a non-constant mobility end up not 
 changing the result. The role of fluid flow in these two problems will als
 o briefly be discussed.
LOCATION:Seminar Room 1\, Newton Institute
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