Abstract. Using Franke's methods we construct new examples of exotic equivalences. We show that for any symmetric ring spectrum R whose graded homotopy ring π * R is concentrated in dimensions divisible by a natural number N ≥ 5 and has homological dimension at most three, the homotopy category of R-modules is equivalent to the derived category of π * R. The Johnson-Wilson spectrum E(3) and the truncated Brown-Peterson spectrum BP 2 for any prime p ≥ 5 are our main examples. If additionally the homological dimension of π * R is equal to two, then the homotopy category of R-modules and the derived category of π * R are triangulated equivalent. Here the main examples are E(2) and BP 1 at p ≥ 5. The last part of the paper discusses a triangulated equivalence between the homotopy category of E(1)-local spectra at a prime p ≥ 5 and the derived category of Franke's model. This is a theorem of Franke and we fill a gap in the proof.
IntroductionLet R be a symmetric ring spectrum and suppose that the homotopy ring π * R of R is concentrated in dimensions divisible by some natural number N ≥ 2. Further assume that the graded global homological dimension gl.dim π * R of π * R is less than N . Using Franke's methods from [5], the paper [10] constructs a functor R : D(π * R) → Ho(Mod -R). Here Ho(Mod -R) is the homotopy category of Mod-R, the model category of module spectra over R and D(π * R) is the derived category of π * R which is by definition the homotopy category of differential graded π * R-modules. The functor R has many interesting properties: It commutes with suspensions, is compatible with homology and homotopy groups, and restricts to an equivalence between the full subcategories of at most one-dimensional objects. In case when gl.dim π * R < N − 1, then R restricts to an equivalence between the full subcategories of at most two dimensional objects. As an application of the latter fact, one concludes that R : D(π * R) → Ho(Mod -R) is an equivalence of categories if N ≥ 4 and gl.dim π * R ≤ 2. These facts are proved in [10]. In particular, the latter result improves a classification theorem by Wolbert [14]. This paper extends the results of [10] to homological dimension three. More precisely we prove the following: Theorem 1.1.1. Let R be a symmetric ring spectrum such that π * R is concentrated in degrees divisible by a natural number N ≥ 2 and assume that the graded global homological dimension of π * R is less than N − 1. Then the functor R : D(π * R) → Ho(Mod-R) restricts to an equivalence of the full subcategories of at most three dimensional objects.As a consequence we obtain: Corollary 1.1.2. Let R be a symmetric ring spectrum such that π * R is concentrated in degrees divisible by a natural number N ≥ 5 and assume that the graded global homological dimension of π * R is less than or equal to three. Then the functor R : D(π * R) → Ho(Mod-R) is an equivalence of categories.Examples to which this corollary applies are the Johnson-Wilson spectrum E(3) and the truncated Brown-Peterson spectrum BP 2 at any pri...