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SUMMARY:Obstructions to homotopy sections of curves over number fields - W
 ickelgren\, K (Stanford)
DTSTART:20090728T130000Z
DTEND:20090728T140000Z
UID:TALK19273@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Grothendieck's section conjecture is analogous to equivalences
  between fixed points and homotopy fixed points of Galois actions on relat
 ed topological spaces. We use cohomological obstructions of Jordan Ellenbe
 rg coming from nilpotent approximations to the curve to study the sections
  of etale pi_1 of the structure map. We will relate Ellenberg's obstructio
 ns to Massey products\, and explicitly compute mod 2 versions of the first
  and second for P^1-{0\,1\,infty} over Q. Over R\, we show the first obstr
 uction alone determines the connected components of real points of the cur
 ve from those of the Jacobian.
LOCATION:Seminar Room 1\, Newton Institute
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