{"paper":{"title":"Revisiting constraints on primordial vector modes and implications for sourced magnetic fields and observed $EB$ power spectrum","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"Cosmological data tightly bound neutrino-sustained vector modes, showing they cannot source observed magnetic fields or the EB power spectrum.","cross_cats":[],"primary_cat":"astro-ph.CO","authors_text":"Kaito Yura, Kiyotomo Ichiki, Shohei Saga, Shuichiro Yokoyama","submitted_at":"2026-05-13T05:11:09Z","abstract_excerpt":"We revisit regular primordial vector modes sustained by the anisotropic stress of free-streaming neutrinos. We consider two classes of neutrino-sector initial conditions, the neutrino velocity isocurvature mode ($\\nu\\mathrm{VI}$) and the neutrino octupole mode ($\\nu\\mathrm{OCT}$). We update their observational constraints using current cosmological data, and examine the impact of including the BICEP/Keck 2018 $B$-mode polarization data. From an MCMC analysis, we obtain the 95\\% C.L. upper bounds on the vector-to-scalar ratio as $r_\\mathrm{v}<1.55\\times10^{-4}$ and $r_\\mathrm{v}<1.04\\times10^{-"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"From an MCMC analysis, we obtain the 95% C.L. upper bounds on the vector-to-scalar ratio as r_v < 1.55×10^{-4} and r_v < 1.04×10^{-2} for the νVI and νOCT modes at k0 = 0.01 Mpc^{-1}. We show that even a fully helical primordial vector mode cannot reproduce the currently observed EB signal while remaining consistent with parity-even CMB constraints.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"The assumption that regular primordial vector modes are sustained by the anisotropic stress of free-streaming neutrinos under the specific neutrino velocity isocurvature (νVI) and octupole (νOCT) initial conditions.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Updated constraints on neutrino-sustained primordial vector modes imply magnetic fields too weak to seed observations and cannot reproduce the EB power spectrum while satisfying parity-even limits.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"Cosmological data tightly bound neutrino-sustained vector modes, showing they cannot source observed magnetic fields or the EB power spectrum.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"0fdefc08848f8d0c00b5d1d40991ca6388eeb8e91af3b48705ed21d5c59a641e"},"source":{"id":"2605.13016","kind":"arxiv","version":1},"verdict":{"id":"ea6ef95c-2c83-4286-9c82-c56d7d16fda3","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-14T18:35:37.725185Z","strongest_claim":"From an MCMC analysis, we obtain the 95% C.L. upper bounds on the vector-to-scalar ratio as r_v < 1.55×10^{-4} and r_v < 1.04×10^{-2} for the νVI and νOCT modes at k0 = 0.01 Mpc^{-1}. We show that even a fully helical primordial vector mode cannot reproduce the currently observed EB signal while remaining consistent with parity-even CMB constraints.","one_line_summary":"Updated constraints on neutrino-sustained primordial vector modes imply magnetic fields too weak to seed observations and cannot reproduce the EB power spectrum while satisfying parity-even limits.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"The assumption that regular primordial vector modes are sustained by the anisotropic stress of free-streaming neutrinos under the specific neutrino velocity isocurvature (νVI) and octupole (νOCT) initial conditions.","pith_extraction_headline":"Cosmological data tightly bound neutrino-sustained vector modes, showing they cannot source observed magnetic fields or the EB power spectrum."},"references":{"count":46,"sample":[{"doi":"","year":2013,"title":"Cosmological Magnetic Fields: Their Generation, Evolution and Observation","work_id":"b101da28-b381-4bc0-9176-e19d6d868643","ref_index":1,"cited_arxiv_id":"1303.7121","is_internal_anchor":true},{"doi":"","year":1992,"title":"Rebhan, Large-Scale Rotational Perturbations of a Friedmann Universe with Collisionless Matter and Pri- mordial Magnetic Fields, ApJ392, 385 (1992)","work_id":"540969b0-f69c-4205-a21e-3c9a78c31511","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2004,"title":"Observable primordial vector modes","work_id":"96128296-ea06-440e-a335-149e2000c5cf","ref_index":3,"cited_arxiv_id":"astro-ph/0403583","is_internal_anchor":true},{"doi":"","year":2012,"title":"Constraint on the primordial vector mode and its magnetic field generation from seven-year Wilkinson Microwave Anisotropy Probe Observations","work_id":"a5a3f9a7-858b-4906-844f-4fb36e0c382c","ref_index":4,"cited_arxiv_id":"1112.4705","is_internal_anchor":true},{"doi":"","year":2014,"title":"Constraining primordial vector mode from B-mode polarization","work_id":"6c4631b0-dfe0-4dd3-8252-5dca98c9d001","ref_index":5,"cited_arxiv_id":"1405.4810","is_internal_anchor":true}],"resolved_work":46,"snapshot_sha256":"3d4d03368b452884f50029cc8bec6bf9a03b65f708f0429480463e50ac550f85","internal_anchors":26},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}