{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"43ceca8d555ad21dcc3b36ef0658bf245bf851c4c4638d36790df04e287e74ae","created":"2026-10-03T07:18:05Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","abde15c8ce0348cfcddbcfced9cdb9e83db5f20569ff8b484d8e25d5d199f364"],"salt":"ca33cc1d8e08a1a54fa59668b978059a5be7573ac18fed91c0bd9ee913288e46","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"hep.strong-cp.pq-quality","kind":"phenomenon","literature_status":"open","n":"1","parents":[{"note":"","parent_revision":"abde15c8ce0348cfcddbcfced9cdb9e83db5f20569ff8b484d8e25d5d199f364","relation":"special_case"}],"plain":"The axion solution needs a symmetry to be almost exact, but gravity is expected to break all such global symmetries slightly. Even a tiny breaking would spoil the solution.","posed_since":"1992","precise":"Planck-suppressed operators $O \\sim \\Phi^n / M_{\\mathrm{Pl}}^{(n-4)}$ shift $\\theta_{\\mathrm{bar}}$ by $\\sim f_a^n / (M_{\\mathrm{Pl}}^{(n-4)} m_a^2 f_a^2)$; keeping $\\mid\\theta_{\\mathrm{bar}}\\mid < 1e-10$ for $f_a \\sim 1e10\\,\\mathrm{GeV}$ requires n > ~ 10. An answer is a UV mechanism (gauge discrete symmetries, composite or extra-dimensional axions) that provably forbids operators up to the required n with predicted low-energy signatures.","problem_ref":null,"references":"","settled_by":"A UV-complete model with the required protection and a distinct prediction, for example heavy axions or modified axion couplings, confirmed by experiment.","status_note":"","title":"How is the Peccei-Quinn symmetry protected from gravitational breaking?","topic_ref":"417555880359201cc195a916f3b947e690164dade4e3ac924d6e5d98d0f88eb7"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"b3791f1778bc4fdaf9902ddb85fd7e51008cc9db779ece0bce99c99898bdbed3","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"5a8bd69d5b0eed66a0c2d6ef4e8c6eabeadf88ecc89f2d2cc05f238a8054ec39","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"7bvSaTrhFfvxKFfLOOrVmgbQ4kIpsdD3xUGDk3H6a_yEtwwfHrUHNuXNQqOhEi_BPEODIY5ZG212JXtCaAYPCA"},"schema":"pubphys.envelope/1"},"record_hash":"b3791f1778bc4fdaf9902ddb85fd7e51008cc9db779ece0bce99c99898bdbed3","leaf_index":1582}