Operadic comodules and (co)homology theories

Abstract

An operad describes a category of algebras and a (co)homology theory for these algebras may be formulated using the homological algebra of operads. A morphism of operads $f:\mathcal{O}\rightarrow\mathcal{P}$ describes a functor allowing a $\mathcal{P}$-algebra to be viewed as an $\mathcal{O}$-algebra. We show that the $\mathcal{O}$-algebra (co)homology of a $\mathcal{P}$-algebra may be represented by a certain operadic comodule. Thus filtrations of this comodule result in spectral sequences computing the (co)homology. As a demonstration we study operads with a filtered distributive law; for the associative operad we obtain a new proof of the Hodge decomposition of the Hochschild cohomology of a commutative algebra. This generalises to many other operads and as an illustration we compute the post-Lie cohomology of a Lie algebra.