{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"adcd02b2117414f88374a6b389c05acfaebacaad945e7c928ad2e7560cf98005","created":"2026-10-03T07:18:01Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"350ae525b948c76734ef510ecc65f975e89ad9d12a01d5056c0eeb9cf8a0bee7","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"classification","assisted_by":[],"external_id":"cm.sign-problem-numerics.intrinsic-sign-problem","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[],"plain":"Many phases of matter with one-way edge currents provably cannot be simulated sign-free by any model built from local terms. Which other phases share this obstruction is open.","posed_since":"2017","precise":"Ringel and Kovrizhin (2017) and Golan, Smith and Ringel (2020) showed that chiral topological phases for which exp(2 pi i c/24) (c the chiral central charge) differs from every topological spin cannot be realized by any local sign-free Hamiltonian. Determine whether non-chiral topological orders, gapless phases (e.g. non-Fermi liquids or Fermi surfaces with nontrivial Luttinger volume) or symmetry-enriched phases carry intrinsic sign problems, and give a complete criterion. An answer is a classification with proofs.","problem_ref":null,"references":"","settled_by":"A theorem extending the chiral criterion to all gapped phases, or explicit sign-free local models for the remaining phases.","status_note":"The chiral case covered by the topological-spin criterion was settled by 2020; non-chiral and gapless cases remain open.","title":"Which phases of matter carry an intrinsic sign problem","topic_ref":"91e71237aaab9c02133089fdeea13d2a6f819a14e160de99c6f929cdb211535a"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"494b3b4a46867e7fcd130a4ba1e211152783c5f51fd08f0d9c721e9a6da663f3","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"c7f495933bdf6c5b00b2a291b3b0abc902588e92ed5b945ce434fa0b3117c887","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"1fSUcwE5luaQKiDF-_vcgRoQInaPH0hp1mtb4NpRmoMp-QB8CkcEGMx8vPLY_J4n7boz5NABYeTv3cfTlaiRAg"},"schema":"pubphys.envelope/1"},"record_hash":"494b3b4a46867e7fcd130a4ba1e211152783c5f51fd08f0d9c721e9a6da663f3","leaf_index":1155}