Noncommutative principal bundles and central extensions

Abstract

Motivated by the classical theory of spin structures, we develop a theory for lifting free C${}^{\ast }$-dynamical systems, a.k.a. noncommutative principal bundles, along central extensions. This theory extends the bundle-theoretic notion of spin structures and yields a complete existence and classification result for such lifts. Using factor system techniques and Picard formalism, our approach introduces new invariants and obstruction classes, thereby unifying geometric, cohomological, and operator-algebraic perspectives. A range of examples demonstrates the scope of the theory.

31 pages. Example in Section 4.6 corrected and updated; minor typos corrected. All comments are welcome