{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"c3843a34cc1fcdc86aa44742da7a91d377dfc8b44d17117085af83b02ac95618","created":"2026-10-03T07:18:05Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"c2c5f248f4a95a9df98ece0bcbc3b5f180260b5fff80df1d7a12be1ced97bd92","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"proof","assisted_by":[],"external_id":"hep.strong-cp.theta-physicality","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"A few theorists argue that, done carefully, the strong-force theory never produces the forbidden effects, so there is no puzzle. Most others say the standard reasoning holds, and the disagreement has not been settled.","posed_since":"2020","precise":"Determine whether CP-odd observables in QCD ($d_{n}$, the $\\theta$ dependence of the vacuum energy and of hadron matrix elements) depend on $\\theta_{\\mathrm{bar}}$ when the infinite-volume limit and the sum over topological sectors are taken in the order argued by Ai, Cruz, Garbrecht and Tamarit (arXiv:2001.07152). An answer is a proof or a lattice computation showing $d_{n}$ proportional to $\\theta_{\\mathrm{bar}}$, or the opposite.","problem_ref":null,"references":"","settled_by":"A rigorous treatment of the $\\theta$-dependence of CP-odd correlators in QCD, cross-checked by lattice computations of $d_n$ at imaginary or small real $\\theta$.","status_note":"Benabou, Hook, Manzari, Murayama and Safdi (arXiv:2510.18951, 2025) and Khoze (arXiv:2512.06827, 2025) argue $\\theta$ is physical; Ai, Garbrecht and Tamarit replied (arXiv:2511.04216, 2025) and the exchange continues in 2026 (arXiv:2601.18248); the majority view keeps the strong CP problem.","title":"Does a nonzero $\\theta$ produce observable CP violation in QCD?","topic_ref":"417555880359201cc195a916f3b947e690164dade4e3ac924d6e5d98d0f88eb7"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"6225d2eff4cbd4b5c79cd3684ca8168f4d9c577c045cad3ebd0d05a9ce7f98ed","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"5b3448c8c3ccca450c670b89f6b21d3590515b83d0555b2f0c68223ed9564654","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"NXhIVKjA-VLfi0ZIMRyV4VMbjPVNL1Dp4yRHFOnv0lr2b9mUDtHq-3LCZ62GeQ8yynRMMFr9unzjcxl6FEkpDw"},"schema":"pubphys.envelope/1"},"record_hash":"6225d2eff4cbd4b5c79cd3684ca8168f4d9c577c045cad3ebd0d05a9ce7f98ed","leaf_index":1580}