{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"034cbabf1f2010f4ce15012bf024e3db8f335695dc90aa4da511b963e3ddefa6","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["a87240394c001c90c7ea93a8c21346d60ca346b17fe614b6c98ba94f349b862e","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"333a717d74827314c266e2bc43c0ff2a99eb6fe1b4a1ff4e5f709477fba977c4","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":["ai:gpt-5.5"],"external_id":"amo.unitary-fermi-transport.spin-diffusion-bound","kind":"well-posed","literature_status":"contested","n":"2","parents":[],"plain":"When up and down spins are separated, strong collisions slow how fast they mix back. Experiments suggest a floor of about $\\hbar/m$, but two kinds of measurement disagree.","posed_since":"2011","precise":"Unitary Fermi gas in 3D (and 2D). Determine the minimum longitudinal spin diffusivity $D_s$ and transverse diffusivity $D_{\\perp}$ in units of $\\hbar/m$, and whether a universal bound $D \\ge c \\hbar/m$ holds. Answer: the value of $c$ for each, and a theory explaining the difference.","problem_ref":"a87240394c001c90c7ea93a8c21346d60ca346b17fe614b6c98ba94f349b862e","references":"","settled_by":"Homogeneous measurements of both diffusivities in the same apparatus near $T_{c}$, with a theory that reproduces both.","status_note":"Longitudinal (Sommer et al. 2011, about $6.3\\,\\hbar/\\mathrm{m}$) and transverse (Bardon et al. 2014, about $1.3\\,\\hbar/\\mathrm{m}$) minima differ by about a factor of 5, and spin-hydrodynamics work continues in 2026 (arXiv:2607.29647).","title":"Universal lower bound on spin diffusion in strongly interacting fermions","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"5c54dbf2a74d90c8d342c6993ee52de51498c77998eb3d2be8f5d2a3b62b8dd6","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"3bf2f4d058aa3eb3c527f3bb79842801151b9988d3562c20cb4e135d74d1d0f4","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"hteKfGYKBchYuPCjv5s9twWv01JmAVNZJFAuIXetp2X_m8aacq52GmoP7dt_jc9GxgQt2YvvKF73FiXmGJrmBA"},"schema":"pubphys.envelope/1"},"record_hash":"5c54dbf2a74d90c8d342c6993ee52de51498c77998eb3d2be8f5d2a3b62b8dd6","leaf_index":2292}