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SUMMARY:Automorphisms of free groups\, hairy graphs and modular forms - Ka
 ren Vogtmann (Cornell)
DTSTART:20120207T170000Z
DTEND:20120207T180000Z
UID:TALK36341@talks.cam.ac.uk
CONTACT:Christopher Brookes
DESCRIPTION:The group  of outer automorphisms of a free group  acts on a
  space of\nfinite graphs known as Outer space\, and a classical theorem of
  Hurwicz\nimplies that the homology of the quotient space is an invariant 
 of the\ngroup. Kontsevich related the homology of this quotient to the Lie
 \nalgebra cohomology of a certain infinite-dimensional symplectic Lie\nalg
 ebra.  Using this connection\, S. Morita discovered a series of new\nhomo
 logy classes for Out(F_n).  We reinterpret Morita's classes in\nterms of 
 hairy graphs\, and show how this leads to the construction of\nlarge numbe
 rs of new classes\, including some based on classical\nmodular forms for S
 L(2\,Z). (joint work with J. Conant and M.\nKassabov).\n
LOCATION:MR15
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