Rectification of enriched ∞-categories
RUNE HAUGSENGWe prove a rectification theorem for enriched ∞-categories: If V is a nice monoidal model category, we show that the homotopy theory of ∞-categories enriched in V is equivalent to the familiar homotopy theory of categories strictly enriched in V. It follows, for example, that ∞-categories enriched in spectra or chain complexes are equivalent to spectral categories and dg-categories. A similar method gives a comparison result for enriched Segal categories, which implies that the homotopy theories of n-categories and (∞, n)-categories defined by iterated ∞-categorical enrichment are equivalent to those of more familiar versions of these objects. In the latter case we also include a direct comparison with complete n-fold Segal spaces. Along the way we prove a comparison result for fibrewise simplicial localizations potentially of independent use. 18D2, 55U35; 18D50, 55P48
IntroductionIn [13], David Gepner and I set up a general theory of "weakly enriched categories" -more precisely, we introduced a notion of ∞-categories enriched in a monoidal ∞-category, and constructed an ∞-category of these objects where the equivalences are the natural analogue of fully faithful and essentially surjective functors in this context. In this paper we are interested in the situation where the monoidal ∞-category we enrich in can be described by a monoidal model category -this applies to many, if not most, interesting examples of monoidal ∞-categories. If V is a model category, then inverting the weak equivalences W gives an ∞-category V[W −1 ]; if V is a monoidal model category, then V[W −1 ] inherits a monoidal structure, so our theory produces an ∞-category of V[W −1 ]-enriched ∞-categories. On the other hand, there is also often a model structure on ordinary V-enriched categories (cf. [19,6,32,24]) where the weak equivalences are the so-called DK-equivalences, namely the functors that are weakly fully faithful (i.e. given by weak equivalences in V on morphism objects), and essentially surjective (up to homotopy). Our main goal in this paper is to prove a rectification theorem in this setting: In particular, V[W −1 ]-enriched ∞-categories can be rectified to V-categories: every V[W −1 ]-enriched ∞-category is equivalent to one coming from a category enriched in V. We will state and prove a precise version of this result in §5. The precise meaning of "nice" required applies, for example, to the category of chain complexes over a ring with the usual projective model structure, and certain model structures on symmetric spectra. We can therefore conclude that the ∞-category of spectral categories is equivalent to that of spectral ∞-categories, and the ∞-category of dg-categories to that of ∞-categories enriched in the derived ∞-category of abelian groups. We will prove a precise version of this theorem in §6. From this we can conclude that the homotopy theories of n-categories and (∞, n)-categories constructed in [13, §6.1] using iterated enrichment are equivalent to those construct...