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Dimension of the Torelli group for Out(F_n)


Speaker: Dan Margalit, University of Utah
Location: 1147 MSB
Start time: Tue, Apr 4 2006, 2:30PM

(This lecture is part of BATS) Let T_n be the kernel of the natural map from Out(F_n) to GL(n,Z). We use combinatorial Morse theory to prove that T_n has an Eilenberg-MacLane space which is (2n-4)-dimensional and that H_{2n-4}(T_n,Z) is not finitely generated (n at least 3). In particular, this recovers the result of Krstic-McCool that T_3 is not finitely presented. We also give a new proof of the fact, due to Magnus, that T_n is finitely generated. This is joint work with Mladen Bestvina and Kai-Uwe Bux.