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Collective motion in large deviations of active particles.

Yann-Edwin Keta1,2,3, Étienne Fodor1,4, Frédéric van Wijland2

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We analyzed rare events in active particle systems, finding that biasing particle motion induces collective movement and alignment. A finite field is necessary for spontaneous symmetry breaking and polar order emergence.

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Area of Science:

  • Physics
  • Statistical Mechanics
  • Soft Matter Physics

Background:

  • Collective motion is crucial in active matter systems.
  • Understanding large deviation events provides insights into system dynamics.
  • Phase transitions in driven systems are key to emergent behavior.

Purpose of the Study:

  • To analyze collective motion during rare events in active particle systems.
  • To investigate the dynamical phase transition to collective motion under biased conditions.
  • To understand the emergence of polar order and symmetry breaking.

Main Methods:

  • Numerical simulations of active particle systems.
  • Analytical calculations, including exact solutions for two-particle systems.
  • Optimal-control theory for analyzing biased dynamics.
  • Fluctuating hydrodynamic theory for many-particle systems.

Main Results:

  • Collective motion and particle alignment emerge during large deviation events.
  • A dynamical phase transition to collective motion is observed when active work is biased.
  • Spontaneous symmetry breaking requires a finite biasing field, even in large systems.
  • Polar order is captured by a proposed fluctuating hydrodynamic theory.

Conclusions:

  • Biasing active particle systems can induce collective motion and polar order.
  • Finite fields are essential for symmetry breaking and emergent collective behavior.
  • The developed hydrodynamic theory effectively describes the biased state dynamics.