Stable rational cohomology of automorphism groups of free groups and the integral cohomology of moduli spaces of graphs

C. A. Jensen
2002 Publicacions matemàtiques  
It is not known whether or not the stable rational cohomology groupsH * (Aut(F∞); Q) always vanish (see Hatcher in [5] and Hatcher and Vogtmann in [7] where they pose the question and show that it does vanish in the first 6 dimensions). We show that either the rational cohomology does not vanish in certain dimensions, or the integral cohomology of a moduli space of pointed graphs does not stabilize in certain other dimensions. Similar results are stated for groups of outer automorphisms. This
more » ... tomorphisms. This yields that H 5 (Qm; Z), H 6 (Qm; Z), and H 5 (Qm; Z) never stabilize as m → ∞, where the moduli spacesQm and Qm are the quotients of the spinesXm and Xm of "outer space" and "auter space", respectively, introduced in [3] by Culler and Vogtmann and [6] by Hatcher and Vogtmann.
doi:10.5565/publmat_46102_06 fatcat:gznrlv3ymzefhl3447sh2ti3r4