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# Asian Journal of Mathematics

## Volume 21 (2017)

### Number 4

### Quantising proper actions on $\mathrm{Spin}^c$-manifolds

Pages: 631 – 686

DOI: http://dx.doi.org/10.4310/AJM.2017.v21.n4.a2

#### Authors

#### Abstract

Paradan and Vergne generalised the quantisation commutes with reduction principle of Guillemin and Sternberg from symplectic to $\mathrm{Spin}^c$-manifolds. We extend their result to noncompact groups and manifolds. This leads to a result for cocompact actions, and a result for non-cocompact actions for reduction at zero. The result for cocompact actions is stated in terms of $K$-theory of group $C^{*}$-algebras, and the result for non-cocompact actions is an equality of numerical indices. In the non-cocompact case, the result generalises to $\mathrm{Spin}^c$-Dirac operators twisted by vector bundles. This yields an index formula for Braverman’s analytic index of such operators, in terms of characteristic classes on reduced spaces.

#### Keywords

$\mathrm{Spin}^c$-manifolds, geometric quantisation, quantisation commutes with reduction, proper Lie group actions, noncompact index theorem

#### 2010 Mathematics Subject Classification

Primary 53C27. Secondary 53D20, 53D50, 58J20, 81S10.

Paper received on 2 July 2015.