JournalsjncgVol. 16, No. 3pp. 1103–1135

Cyclic cocycles in the spectral action

  • Teun D. H. van Nuland

    Radboud University, Nijmegen, Netherlands
  • Walter D. van Suijlekom

    Radboud University, Nijmegen, Netherlands
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We show that the spectral action, when perturbed by a gauge potential, can be written as a series of Chern–Simons actions and Yang–Mills actions of all orders. In the odd orders, generalized Chern–Simons forms are integrated against an odd (b,B)(b,B)-cocycle, whereas, in the even orders, powers of the curvature are integrated against (b,B)(b,B)-cocycles that are Hochschild cocycles as well. In both cases, the Hochschild cochains are derived from the Taylor series expansion of the spectral action Tr(f(D+V))\operatorname{Tr}(f(D+V)) in powers of V=πD(A)V=\pi_D(A), but unlike the Taylor expansion we expand in increasing order of the forms in AA. This extends the work of Connes and Chamseddine (2006), which computes only the scale-invariant part of the spectral action, works in dimension at most 4, and assumes the vanishing tadpole hypothesis. In our situation, we obtain a truly infinite odd (b,B)(b,B)-cocycle. The analysis involved draws from recent results in multiple operator integration, which also allows us to give conditions under which this cocycle is entire, and under which our expansion is absolutely convergent. As a consequence of our expansion and of the gauge invariance of the spectral action, we show that the odd (b,B)(b,B)-cocycle pairs trivially with K1K_1.

Cite this article

Teun D. H. van Nuland, Walter D. van Suijlekom, Cyclic cocycles in the spectral action. J. Noncommut. Geom. 16 (2022), no. 3, pp. 1103–1135

DOI 10.4171/JNCG/500