{
  "annotation_id": "676d6cf2-ecea-4e6e-ba9a-80acdfd87760",
  "date_created": "2026-03-02T18:02:37.267000Z",
  "date_modified": "2026-03-02T18:02:37.267000Z",
  "file_hash": "720bbc8e8278dc9407ffe505111b6b5a3c2c50bf730f0833335811d218fc06b6",
  "private": false,
  "record": {
    "abstract": "It is shown that the spin operator can be described by an algebra which is in\nbetween so(3) and e(2). Relativistic version of the singlet state for two Dirac\nelectrons is discussed. It is shown that a measure of massless particle\u0027s\nextension can be naturally constructed and that this measure corresponds at the\nclassical level to the radius of the Robinson congruence.",
    "arxiv_id": "quant-ph/9501017",
    "authors": [
      "M. Czachor",
      "A. Posiewnik"
    ],
    "categories": [
      "quant-ph"
    ],
    "title": "What happens to spin during the SO(3)-\u003eSE(2) contraction? (On spin and   extended structures in quantum mechanics)",
    "url": "https://arxiv.org/abs/quant-ph/9501017"
  },
  "schema_id": "dorsal/arxiv",
  "source": {
    "execution_id": "ee42e4be-f61d-4d25-94c5-3ff3e869fafb",
    "id": "arXiv Dataset IDs",
    "type": "Model",
    "variant": "snapshot-2026-03-01",
    "version": "0.1.0"
  },
  "user_id": 1000002
}