20.08.2015 Views

process

K-theory and Noncommutative Geometry.pdf

K-theory and Noncommutative Geometry.pdf

SHOW MORE
SHOW LESS
  • No tags were found...

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

334 U. Bunke, T. Schick, M. Spitzweck, and A. ThomDKH 1 .BI Z n /H 0 .BI ƒ 2 Z n /s˛H 3 .BI Z/i c.E/H 2 .BI Z n /ˇ(60)K AF 2 H 3 Nˇ.EI Z/ BH 4 .BI Z/0 0Since K as a subgroup of the free abelian group H 0 .B; ƒ 2 Z n / is free we can choosea lift s as indicated.6.3.5 We now define a map (the underlying pair map)upW Q E ! P.B/as follows. Any Picard stack P 2 PIC.S=B/ comes with a natural map of stacksP ! H 0 .P / (where on the right-hand side we consider a sheaf of sets as a stack). IfP 2 Q E , then H 0 .P / Š E has a natural map to Z jB (see (57)). We define the stackG by the pull-back in stacks on S=BG PEE ¹1º jBZ jB .All squares are two-cartesian, and the outer square is the composition of the two innersquares. We have omitted to write the canonical two-isomorphisms. By constructionE is a sheaf of T n -torsors (see 6.2.5), i.e. by Lemma 6.13 a T n -principal bundle, andG ! E is a gerbe with band T. We setup.P / WD .E; G/:

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!