Segal Group Actions

Abstract

We define a model category structure on a slice category of simplicial spaces, called the "Segal group action" structure whose fibrant-cofibrant objects may be viewed as representing spaces $X$ with a coherent action of a given Segal group (i.e. a group-like, reduced Segal space). We show that this model structure is Quillen equivalent to the projective model structure on $G$-spaces, $\mathcal{S}^{\mathbb{B}G}$, where $G$ is a simplicial group represented by this Segal group. Since Segal group actions are invariant under weak monoidal endofunctors of spaces they enable to construct, for an arbitrary $G$-space $X$, an "equivariant Postnikov tower" which in degree $n$ has $P_nX$ viewed as a space with a coherent action of (the Segal group corresponding to) $P_nG$.