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

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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.