Comptes Rendus
Homological Algebra/Group Theory
Homology and K-theory of the Bianchi groups
[Homologie et K-théorie des groupes de Bianchi]
Comptes Rendus. Mathématique, Volume 349 (2011) no. 11-12, pp. 615-619.

We reveal a correspondence between the homological torsion of the Bianchi groups and new geometric invariants, which are effectively computable thanks to their action on hyperbolic space. We use it to explicitly compute their integral group homology and equivariant K-homology. By the Baum/Connes conjecture, which holds for the Bianchi groups, we obtain the K-theory of their reduced C-algebras in terms of isomorphic images of the computed K-homology. We further find an application to Chen/Ruan orbifold cohomology.

Nous mettons en évidence une correspondance entre la torsion homologique des groupes de Bianchi et de nouveaux invariants géométriques, calculables grâce à leur action sur lʼespace hyperbolique. Nous lʼutilisons pour calculer explicitement leur homologie de groupe à coefficients entiers et leur K-homologie équivariante. En conséquence de la conjecture de Baum/Connes, qui est vérifiée pour ces groupes, nous obtenons la K-théorie de leurs C*-algèbres réduites en termes dʼimages isomorphes de la K-homologie calculée. Nous trouvons dʼailleurs une application à la cohomologie dʼorbi-espace de Chen/Ruan.

Reçu le :
Accepté le :
Publié le :
DOI : 10.1016/j.crma.2011.05.014

Alexander D. Rahm 1

1 Department of Mathematics, Weizmann Institute of Science, Rehovot, Israel
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Alexander D. Rahm. Homology and K-theory of the Bianchi groups. Comptes Rendus. Mathématique, Volume 349 (2011) no. 11-12, pp. 615-619. doi : 10.1016/j.crma.2011.05.014. https://comptes-rendus.academie-sciences.fr/mathematique/articles/10.1016/j.crma.2011.05.014/

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  • Sam Hughes On the equivariant K- and KO-homology of some special linear groups, Algebraic Geometric Topology, Volume 21 (2021) no. 7, pp. 3483-3512 | DOI:10.2140/agt.2021.21.3483 | Zbl:1509.19010
  • Ethan Berkove; Grant S. Lakeland; Alexander D. Rahm The mod 2 cohomology rings of congruence subgroups in the Bianchi groups, Journal of Algebraic Combinatorics, Volume 52 (2020) no. 4, pp. 527-560 | DOI:10.1007/s10801-019-00912-8 | Zbl:1472.11164
  • Bram Mesland; Mehmet Haluk Şengün Hecke operators in KK-theory and the K-homology of Bianchi groups, Journal of Noncommutative Geometry, Volume 14 (2020) no. 1, pp. 125-189 | DOI:10.4171/jncg/361 | Zbl:1473.11112
  • Awais Yousaf; Hanan Alolaiyan; Abdul Razaq; Muhammad Younis Evolution of ambiguous numbers under the actions of a Bianchi group, Journal of Taibah University for Science, Volume 14 (2020) no. 1, p. 615 | DOI:10.1080/16583655.2020.1760511
  • Alexander D. Rahm; Panagiotis Tsaknias Genuine Bianchi modular forms of higher level at varying weight and discriminant, Journal de Théorie des Nombres de Bordeaux, Volume 31 (2019) no. 1, pp. 27-48 | DOI:10.5802/jtnb.1067 | Zbl:1466.11027
  • Alexander D. Rahm On the equivariant K-homology of PSL2 of the imaginary quadratic integers, Annales de l'Institut Fourier, Volume 66 (2016) no. 4, pp. 1667-1689 | DOI:10.5802/aif.3047 | Zbl:1360.55007
  • Ethan Berkove; Alexander D. Rahm The mod 2 cohomology rings of SL2 of the imaginary quadratic integers. With an appendix by Aurel Page, Journal of Pure and Applied Algebra, Volume 220 (2016) no. 3, pp. 944-975 | DOI:10.1016/j.jpaa.2015.08.002 | Zbl:1401.11100
  • Mehmet Haluk Şengün Arithmetic aspects of Bianchi groups, Computations with modular forms. Proceedings of a summer school and conference, Heidelberg, Germany, August–September 2011, Cham: Springer, 2014, pp. 279-315 | DOI:10.1007/978-3-319-03847-6_11 | Zbl:1375.11039
  • Kevin Hutchinson A refined Bloch group and the third homology of SL2 of a field, Journal of Pure and Applied Algebra, Volume 217 (2013) no. 11, pp. 2003-2035 | DOI:10.1016/j.jpaa.2013.01.001 | Zbl:1281.19003
  • Alexander D. Rahm; Mehmet Haluk Şengün On level one cuspidal Bianchi modular forms, LMS Journal of Computation and Mathematics, Volume 16 (2013), pp. 187-199 | DOI:10.1112/s1461157013000053 | Zbl:1294.11062
  • Alexander D. Rahm Higher torsion in the abelianization of the full Bianchi groups, LMS Journal of Computation and Mathematics, Volume 16 (2013), pp. 344-365 | DOI:10.1112/s1461157013000168 | Zbl:1328.11057
  • Alexander D. Rahm The homological torsion of PSL2 of the imaginary quadratic integers, Transactions of the American Mathematical Society, Volume 365 (2013) no. 3, pp. 1603-1635 | DOI:10.1090/s0002-9947-2012-05690-x | Zbl:1307.11065

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