English

Geometric Dirac operator on noncommutative torus and $M_2(\Bbb C)$

Quantum Algebra 2023-06-21 v3 General Relativity and Quantum Cosmology

Abstract

We solve for quantum-geometrically realised spectral triples or `Dirac operators' on the noncommutative torus Cθ[T2]\Bbb C_\theta[T^2] and on the algebra M2(C)M_2(\Bbb C) of 2×22\times 2 matrices with their standard quantum metrics and associated quantum Levi-Civita connections. For Cθ[T2]\Bbb C_\theta[T^2], we obtain an even standard spectral triple but now uniquely determined by full geometric realisability. For M2(C)M_2(\Bbb C), we are forced to the flat quantum Levi-Civita connection and again obtain a natural fully geometrically realised even spectral triple. In both case there is also an odd spectral triple for a different choice of a sign parameter. We also consider an alternate quantum metric on M2(C)M_2(\Bbb C) with curved quantum Levi-Civita connection and find a natural 2-parameter of almost spectral triple in that DD fails to be antihermitian. In all cases, we split the construction into a local tensorial level related to the quantum geometry, where we classify the results more broadly, and the further requirements relating to the Hilbert space structure. We also illustrate the Lichnerowicz formula for D2D^2 which applies in the case of a full geometric realisation.

Keywords

Cite

@article{arxiv.2208.07821,
  title  = {Geometric Dirac operator on noncommutative torus and $M_2(\Bbb C)$},
  author = {E. Lira-Torres and S. Majid},
  journal= {arXiv preprint arXiv:2208.07821},
  year   = {2023}
}

Comments

33 pages latex no figures. Moved the less interesting second quantum metric on M_2(C) into an appendix, corrected typos and added details of Lichnerowicz theorem related D^2 and Laplacian. This is a sequel to 2104.13212 (math.QA)

R2 v1 2026-06-25T01:44:40.757Z