The summability converse for spectral triples on the Sierpiński gasket

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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>log⁡3/log⁡2p>\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 sup⁡m→∞(∑k=13m−1∣f(m,k)∣)1/m≤3.\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.

References

Primary source

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

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