Universality class of the motility-induced phase separation critical point · revision history
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- Title
- Universality class of the motility-induced phase separation critical point
- Plain
- Self-propelled particles that only repel each other can still separate into a dense crowd and a dilute gas, called motility-induced phase separation (MIPS). Whether the critical point where the two phases merge behaves like the ordinary liquid-gas (Ising) critical point is disputed.
- Precise
- Active Brownian particles with purely repulsive interactions phase separate above a critical Peclet number $\mathrm{Pe}_{\mathrm{c}}$ (ratio of self-propulsion to thermal diffusion). Determine the critical exponents $\nu, \beta$ and $\gamma/\nu$ at the MIPS critical point in $d = 2$ and decide whether they equal 2D Ising values or define a different universality class. An answer combines finite-size scaling with controlled corrections and a renormalization-group analysis of the coarse-grained field theory (active model $B+$). In 3D, MIPS coexistence near the critical point is metastable against crystallization (Omar et al. 2021), so the 3D question concerns a metastable critical point.
- Settled by
- Finite-size scaling of the order-parameter distribution at $\mathrm{Pe}_{c}$ in systems large enough to control corrections, consistent with a renormalization-group calculation.
- Kind
- well-posed
- Answer type
- classification
- References
- (empty)
- Literature status
- contested
- Status note
- Large-scale 2D studies (Partridge and Lee 2019; Maggi et al. 2021) and a 2025 3D study find Ising exponents, against an earlier non-Ising report (Siebert et al. 2018); no renormalization-group calculation for active model B+ confirms Ising universality.
- Posed since
- (empty)