Proceedings of the London Mathematical Society Advance Access published online on June 16, 2009
Proceedings of the London Mathematical Society, doi:10.1112/plms/pdp023
© 2009 London Mathematical Society
A Maslov cocycle for unitary groups
Mathematisches Institut
Universität Münster
Einsteinstr. 62
48149 Münster
Germany
tent@uni-muenster.de
Received 24 September 2008.
We introduce a 2-cocycle for symplectic and skew-hermitian hyperbolic groups over arbitrary fields and skew-fields, with values in the Witt group of hermitian forms. This cocycle has good functorial properties: it is natural under extension of scalars and stable, and so it can be viewed as a universal 2-dimensional characteristic class for these groups. Over
and
, it coincides with the first Chern class.
The authors were supported by SFB 478 and SFB 701.
2000 Mathematics Subject Classification 11E70, 19C09, 20G10, 20J05.