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Wagner, Stefan, PhD
Publications (4 of 4) Show all publications
Wagner, S. (2018). Extending characters of fixed point algebras. Axioms, 7(4), Article ID 79.
Open this publication in new window or tab >>Extending characters of fixed point algebras
2018 (English)In: Axioms, ISSN 2075-1680, Vol. 7, no 4, article id 79Article in journal (Refereed) Published
Abstract [en]

A dynamical system is a triple (A, G, α) consisting of a unital locally convex algebra A, a topological group G, and a group homomorphism α: G → Aut(A) that induces a continuous action of G on A. Furthermore, a unital locally convex algebra A is called a continuous inverse algebra, or CIA for short, if its group of units A× is open in A and the inversion map i: A× → A×, a → a-1 is continuous at 1A. Given a dynamical system (A, G, α) with a complete commutative CIA A and a compact group G, we show that each character of the corresponding fixed point algebra can be extended to a character of A. © 2018 by the authors.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
Character, Continuous inverse algebra, Dynamical system, Extension, Fixed point algebra, Maximal ideal
National Category
Algebra and Logic
Identifiers
urn:nbn:se:bth-17355 (URN)10.3390/axioms7040079 (DOI)000456944400011 ()2-s2.0-85056790615 (Scopus ID)
Note

open access

Available from: 2018-11-29 Created: 2018-11-29 Last updated: 2019-02-21
Schwieger, K. & Wagner, S. (2017). Part III, Free Actions of Compact Quantum Groups on C*-Algebras. SIGMA. Symmetry, Integrability and Geometry, 13, Article ID 62.
Open this publication in new window or tab >>Part III, Free Actions of Compact Quantum Groups on C*-Algebras
2017 (English)In: SIGMA. Symmetry, Integrability and Geometry, ISSN 1815-0659, E-ISSN 1815-0659, Vol. 13, article id 62Article in journal (Refereed) Published
Abstract [en]

We study and classify free actions of compact quantum groups on unital C*-algebras in terms of generalized factor systems. Moreover, we use these factor systems to show that all finite coverings of irrational rotation C*-algebras are cleft.

Place, publisher, year, edition, pages
NATL ACAD SCI UKRAINE, INST MATH, 2017
Keywords
free action, C*-algebra, quantum group, factor system, finite covering
National Category
Algebra and Logic
Identifiers
urn:nbn:se:bth-15088 (URN)10.3842/SIGMA.2017.062 (DOI)000407251200001 ()
Note

Open Access

Available from: 2017-08-31 Created: 2017-08-31 Last updated: 2017-09-08Bibliographically approved
Wagner, S. & Schwieger, K. Noncommutative Coverings of Quantum Tori. Mathematica Scandinavica
Open this publication in new window or tab >>Noncommutative Coverings of Quantum Tori
(English)In: Mathematica Scandinavica, ISSN 0025-5521, E-ISSN 1903-1807Article in journal (Other academic) Accepted
Abstract [en]

We investigate a framework for coverings of noncommutative spaces. Furthermore, we study noncommutative coverings of irrational quantum tori and characterize all such coverings that are connected in a reasonable sense.

Keywords
Free action, noncommutative covering, fundamental group, quantum tori, gauge action, connected, Bogoliubov transformation, Schrödinger representation
National Category
Mathematics Algebra and Logic
Identifiers
urn:nbn:se:bth-17514 (URN)
Funder
Carl Tryggers foundation , CTS16:540
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-01-25Bibliographically approved
Wagner, S. Secondary Characteristic Classes of Lie Algebra Extensions.
Open this publication in new window or tab >>Secondary Characteristic Classes of Lie Algebra Extensions
(English)In: Article in journal (Other academic) Accepted
Abstract [en]

We introduce a notion of secondary characteristic classes of Lie algebra extensions. As a spin-off of our construction we obtain a new proof of Lecomte’s generalization of the Chern–Weil homomorphism.

Keywords
Secondary characteristic class, Lie algebra extension
National Category
Mathematics Algebra and Logic
Identifiers
urn:nbn:se:bth-17519 (URN)
Funder
Carl Tryggers foundation , CTS16:540
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-01-25Bibliographically approved
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