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Metastability of Constant-Density Flocks.

Marc Besse1, Hugues Chaté1,2,3, Alexandre Solon1

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Constant-density active matter flocks are metastable, transitioning to a disordered phase with asters and shock lines. This active foam differs from equilibrium systems due to disorder along shock lines, requiring nonperturbative approaches.

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Area of Science:

  • Active matter physics
  • Non-equilibrium statistical mechanics
  • Complex systems

Background:

  • The Toner-Tu field theory describes flocking behavior in active matter.
  • Constant-density Malthusian flocks represent a specific, exactly solvable limit case.
  • Understanding phase transitions and defect formation is crucial in active systems.

Purpose of the Study:

  • Numerically investigate the Toner-Tu field theory under constant density conditions.
  • Confirm known asymptotic scaling laws in the ordered phase.
  • Characterize the stability and emergent phases of these flocks.

Main Methods:

  • Numerical simulations of the Toner-Tu field theory.
  • Analysis of correlation functions and defect structures.
  • Comparison with theoretical predictions and equilibrium systems.

Main Results:

  • Confirmed asymptotic scaling laws for constant-density flocks.
  • Identified metastability and nucleation of defect configurations.
  • Observed transition to a disordered phase with asters and shock lines.
  • Demonstrated that shock lines are the primary source of disorder.

Conclusions:

  • Constant-density flocks are not globally stable and evolve into a disordered state.
  • Active foams exhibit fundamental differences from equilibrium systems due to shock line dynamics.
  • Nonperturbative effects can dominate over perturbative results in active matter, necessitating alternative theoretical frameworks.