The Deligne-Mumford spaces as an operadic homotopy quotient -- Kevin Costello, November 12, 2004

I'll describe how the Deligne-Mumford spaces can be realized as a homotopy quotient, in an operadic sense, of the uncompactified moduli spaces of Riemann surfaces with boundary, by a natural circle action. This is used to show that we can extend two dimensional field theories to the boundary of moduli space by taking circle equivariant cohomology.