Communications in Mathematical Physics

, Volume 316, Issue 2, pp 531–554 | Cite as

Subfactors of Index Less Than 5, Part 3: Quadruple Points

  • Masaki Izumi
  • Vaughan F. R. Jones
  • Scott Morrison
  • Noah Snyder


One major obstacle in extending the classification of small index subfactors beyond \({3 +\sqrt{3}}\) is the appearance of infinite families of candidate principal graphs with 4-valent vertices (in particular, the “weeds” \({\mathcal{Q}}\) and \({\mathcal{Q}'}\) from Part 1 (Morrison and Snyder in Commun. Math. Phys., doi: 10.1007/s00220-012-1426-y, 2012). Thus instead of using triple point obstructions to eliminate candidate graphs, we need to develop new quadruple point obstructions. In this paper we prove two quadruple point obstructions. The first uses quadratic tangles techniques and eliminates the weed \({\mathcal{Q}'}\) immediately. The second uses connections, and when combined with an additional number theoretic argument it eliminates both weeds \({\mathcal{Q}}\) and \({\mathcal{Q}'}\) . Finally, we prove the uniqueness (up to taking duals) of the 3311 Goodman-de la Harpe-Jones subfactor using a combination of planar algebra techniques and connections.


Fusion Category Graph Automorphism Gauge Class Fusion Ring Quadruple Point 
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Copyright information

© The Author(s) 2012

Authors and Affiliations

  • Masaki Izumi
    • 1
  • Vaughan F. R. Jones
    • 2
  • Scott Morrison
    • 2
  • Noah Snyder
    • 3
  1. 1.Department of Mathematics, Graduate School of ScienceKyoto UniversityKyotoJapan
  2. 2.Department of MathematicsUniversity of CaliforniaBerkeleyUSA
  3. 3.Department of MathematicsColumbia UniversityNew YorkUSA

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