Critical motility-induced phase separation in three dimensions is consistent with Ising universality

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Critical active phase transitions are a topic of recent scientific interest and debate.
• Determining the universality class of these transitions requires robust numerical simulations.

Purpose of the Study:

• To resolve controversies regarding active phase transitions.
• To investigate whether active critical exponents align with novel or established universality classes.

Main Methods:

• Conducted large-scale computer simulations of motility-induced phase separation (MIPS).
• Performed finite-size scaling analysis on active Brownian hard spheres in three dimensions (3D).
• Utilized a fluctuating hydrodynamic description for critical dynamics.

Main Results:

• Static and dynamic critical exponents closely match those of the 3D Ising universality class.
• The order parameter field's critical dynamics flow to the Wilson-Fisher fixed point in 3D.
• 3D MIPS and the active Brownian hard sphere phase diagram resemble those of molecular passive fluids.

Conclusions:

• The findings suggest 3D MIPS belongs to the 3D Ising universality class.
• Active systems can exhibit behavior analogous to passive systems despite lacking Boltzmann statistics.
• This work provides a robust numerical investigation into active phase transitions.