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SUMMARY:A new invariant of G2 structures  - Diarmuid Crowley\, Max Planck 
 Bonn
DTSTART:20130227T160000Z
DTEND:20130227T170000Z
UID:TALK41479@talks.cam.ac.uk
CONTACT:Ivan Smith
DESCRIPTION: I will report on recent joint work with Johannes Nordström w
 here we define an invariant of \ndiffeomorphisms and homotopies of a G2 st
 ructure on a closed 7 manifold.  The invariant takes values \nin Z/48 and 
 is defined via the Euler characteristic and signature of a Spin(7) cobound
 ary of the G2 structure.\nI will discuss examples\, calculations for the i
 nvariant to date and its relationship to the mapping class \ngroups of spi
 n 7-manifolds.
LOCATION:MR13
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