The summability converse for spectral triples on the Sierpiński gasket

Let SGSG denote the Sierpiński gasket and let (A,H,D)(A,H,D) be a spectral triple for C(SG)C(SG) inducing the geodesic distance on the gasket. Suppose that it is summable for every p>log3/log2p>\log 3/\log 2, and that (f(m,k))ΠHSGZ(f(m,k))\in\Pi_{HSG}\mathbb{Z} represents its K-homology class. Summability converse. Then

lim supm(k=13m1f(m,k))1/m3.\limsup_{m\to\infty}\left(\sum_{k=1}^{3^{m-1}}|f(m,k)|\right)^{1/m}\leq 3.

This would provide a converse to the preceding characterization of summability for the spectral triples ST(f)ST(f), extending the known implication from bounded sequences to a necessary growth condition for arbitrary spectral triples inducing the geodesic metric. The source does not state whether the converse is resolved.

Sources & referencesView supporting material

Primary source

Erik Christensen, Cristina Ivan and Elmar Schrohe, “Spectral triples and the geometry of fractals”, arXiv:1002.3081 (2011).

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