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On characteristic classes of vector bundles over quantum spheres

Francesco D’Andrea, Giovanni Landi and Chiara Pagani

Vol. 11 (2026), No. 4, 709–745
Abstract

We study the quantization of spaces whose K-theory in the classical limit is the ring of dual numbers ℤ[t]∕(t2). For a compact Hausdorff space we recall necessary and sufficient conditions for this to hold. For a compact quantum space, we give sufficient conditions that guarantee that there is a morphism K0 → ℤ[t]∕(t2) of abelian groups that is compatible with the tensor product of bimodules. Applications include 2-dimensional and 4-dimensional quantum spheres. We discuss in detail the quantum 4-sphere Sq4 coming from quantum symplectic groups, whose K-theory is generated by the Euler class of the instanton bundle. We give explicit formulas for the projections of vector bundles on Sq4 associated to the principal SU ⁡ q(2)-bundle Sq7 → Sq4 via irreducible corepresentations of SU ⁡ q(2), and compute their characteristic classes.

Keywords
quantum spaces, K-theory, principal and associated vector bundles, instantons on $q$-spheres, Euler class, Chern characters
Mathematical Subject Classification
Primary: 20G42
Secondary: 46L89, 58B34
Milestones
Received: 5 February 2026
Accepted: 9 May 2026
Published: 21 October 2026
Authors
Francesco D’Andrea
Dipartimento di Matematica e Applicazioni
Università di Napoli Federico II and INFN-Napoli
Napoli
Italy
Giovanni Landi
Matematica
Università di Trieste and INFN-Trieste
Trieste
Italy
Chiara Pagani
Dipartimento di Matematica e Applicazioni
Università di Napoli Federico II and INFN-Napoli
Napoli
Italy