Abstract
The principal graph X of a subfactor with finite Jones index is one of the important algebraic invariants of the subfactor. If Δ is the adjacency matrix of X we consider the equation Δ = U + U −1. When X has square norm ≤ 4 the spectral measure of U can be averaged by using the map u→ u −1, and we get a probability measure \(\varepsilon\) on the unit circle which does not depend on U. We find explicit formulae for this measure \(\varepsilon\) for the principal graphs of subfactors with index ≤ 4, the (extended) Coxeter-Dynkin graphs of type A, D and E. The moment generating function of \(\varepsilon\) is closely related to Jones’ Θ-series.
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Communicated by Y. Kawahigashi
D.B. was supported by NSF under Grant No. DMS-0301173.
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Banica, T., Bisch, D. Spectral Measures of Small Index Principal Graphs. Commun. Math. Phys. 269, 259–281 (2007). https://doi.org/10.1007/s00220-006-0122-1
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DOI: https://doi.org/10.1007/s00220-006-0122-1