{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"bafb414658cced173f84c50f4628099f9f1890d57e79a011e921cb5eda5d4821","created":"2026-10-03T07:17:54Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"84835aebdf930c49aa9881f31e45bf771b7a0a8d9833c5408f5a1e92c44f648f","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"amo.unitary-fermi-transport.spin-diffusion-bound","kind":"well-posed","literature_status":"contested","n":"1","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":null,"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":"b4f1be3df3747cf1d62d5ccbaa2ed5e283f70c00fc559fc9419649add747e05b"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"a87240394c001c90c7ea93a8c21346d60ca346b17fe614b6c98ba94f349b862e","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"3ae4d467a48f09ef61bc0cd3269a270e701b9bee3b44a0a36f1bcc3ff6928e32","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"uw08syA5ZjDsur8uKNUurZHnh-ZeKxSZpJ2yPhm3CDJDUVhsd76KLABHvcGqsPbc95gFjSbVqAHGP0rAZ7G5DQ"},"schema":"pubphys.envelope/1"},"record_hash":"a87240394c001c90c7ea93a8c21346d60ca346b17fe614b6c98ba94f349b862e","leaf_index":476}