Enriched Koszul duality for dg categories

Abstract

It is well-known that the category of small dg categories dgCat, though it is monoidal, does not form a monoidal model category. In this paper we construct a monoidal model structure on the category of pointed curved coalgebras ptdCoa* and show that the Quillen equivalence relating it to dgCat is monoidal. We also show that dgCat is a ptdCoa*-enriched model category. As a consequence, the homotopy category of dgCat is closed monoidal and is equivalent as a closed monoidal category to the homotopy category of ptdCoa*. In particular, this gives a conceptual construction of a derived internal hom in dgCat. As an application we obtain a new description of simplicial mapping spaces in dgCat and a calculation of their homotopy groups in terms of Hochschild cohomology groups, reproducing and slightly generalizing well-known results of To\"en. Comparing our approach to To\"en's, we also obtain a description of the core of Lurie's dg nerve in terms of the ordinary nerve of a discrete category.