{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ef12d1d811d9f69219dc6514df9c8740f75dbd41640110ce85c631f16923e1b0","created":"2026-10-03T07:18:02Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","8f01e07130ca052ceb0cc44241859d89ccc352e3fc638b3dd4f94da9479c6f49"],"salt":"b76dbf94ac33577a3cbd8c73a44bb68a6a5a7f2f9f3222190fc109a779e8e715","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"cosmo.dark-energy.phantom-crossing","kind":"well-posed","literature_status":"open","n":"1","parents":[{"note":"","parent_revision":"8f01e07130ca052ceb0cc44241859d89ccc352e3fc638b3dd4f94da9479c6f49","relation":"special_case"}],"plain":"The current best fits say dark energy was once stronger than empty-space energy and is now weaker. A simple rolling field cannot do that, so either the fits mislead or the physics is more exotic.","posed_since":"2005","precise":"DESI $w0-wa$ best fits imply $w < -1$ at redshift $z > \\sim 0.4$ and $w > -1$ today, which a single minimally coupled canonical scalar field cannot produce. Determine whether the data require crossing $w = -1$ when fitted with physically consistent models (thawing quintessence, coupled dark energy and dark matter, scalar-tensor gravity) or whether the crossing is an artifact of the linear parametrization and priors.","problem_ref":null,"references":"","settled_by":"Model comparison using reconstructions of w(z) in redshift bins and physical models, showing whether non-crossing models fit as well as crossing ones.","status_note":"","title":"Does the dark energy equation of state cross $w = 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