{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"685c13bc04021033670d93294e557e601cce296c6df06d7b40bc406fc0886198","created":"2026-10-03T07:18:02Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"c0861209fd079412aacc5314f5c53e0ce812c12d354b4a175608daf7a2f3babc","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"cosmo.structure-growth-neutrino-mass.reionization-optical-depth","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Free electrons released when the first galaxies ionized hydrogen scatter microwave background light, an effect measured by a number called the optical depth. If it is larger than the Planck value, several current tensions, including the neutrino-mass one, ease.","posed_since":"","precise":"Planck low-multipole EE polarization gives $\\tau = 0.054 \\pm 0.007$. Sailer, Farren, Ferraro and White (2025, arXiv:2504.16932) show that a larger $\\tau$ removes the DESI BAO versus CMB tension in extended models, including the preference for very small or negative sum $m_\\nu$, but conflicts with Planck large-scale polarization. Determine $\\tau$ with $\\sigma(\\tau)$ below 0.003 from an independent large-angle E-mode measurement or from 21-cm and kinetic Sunyaev-Zeldovich reionization histories, and state whether it agrees with the Planck value.","problem_ref":null,"references":"","settled_by":"Large-angle E-mode polarization from LiteBIRD or a ground or balloon experiment such as CLASS, cross-checked with reionization histories from 21-cm and kSZ data.","status_note":"","title":"Is the CMB reionization optical depth underestimated?","topic_ref":"7f5d118cb8a64bd99639aa18f99daf7cb794d9366c6bec82eeea82eef99d0ccd"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"e78507b756e7a013b0d7f37b3e96ea34143249f0d9d881d9bd947f4a2997d8b4","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"63a23ecbe8b7d23ed8a77f4031edec686032e50e9c2957a6af5c0e02defb1450","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"o5B509ebzIvXloKWPGn3Yqnn9y9nWOSP-qHvrGkr7IfDcsP0SCCPzny_HDFDsqk8P7pnGB_hE9uN-bMfXJUeBg"},"schema":"pubphys.envelope/1"},"record_hash":"e78507b756e7a013b0d7f37b3e96ea34143249f0d9d881d9bd947f4a2997d8b4","leaf_index":1282}