{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ddabe31ae43e3f61ad1629857d95bb47590fed22df30c8052934114e46682887","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"2b13f397de4c934d732b03553c07995137f3dd34503cb924a9ffee5739256f3c","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"classification","assisted_by":[],"external_id":"bio.active-matter.mips-critical-class","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"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.","posed_since":"","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.","problem_ref":null,"references":"","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.","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.","title":"Universality class of the motility-induced phase separation critical point","topic_ref":"6a008dc19304a289e116a6d6e6371cc6de0ef3d1a904e572d5454f039b2ac217"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"d51e974ed24d10da191834b24cfdb109bf8e6f986afb6e6808c54de63a2359ca","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"735e65c59a39ccca34a1d104462055a9b55ab9d44248b866db9e55ad8be6a75c","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"3HwAixn1C6Y6WwNOfSHa1mBdAw1iH9G83nXT9nsvc1JYNr2aop-hmPAVgGSYwgqN-WzPTox0n9N_jeTpmOhaAw"},"schema":"pubphys.envelope/1"},"record_hash":"d51e974ed24d10da191834b24cfdb109bf8e6f986afb6e6808c54de63a2359ca","leaf_index":723}