The fp-injective module conjecture

Let AA be a ring, and let FpinjA\operatorname{Fpinj} A be the category of fp-injective AA-modules. Write K(InjA)\mathbf K(\operatorname{Inj} A) for the homotopy category of complexes of injective AA-modules, K(FpinjA)\mathbf K(\operatorname{Fpinj} A) for the homotopy category of complexes in FpinjA\operatorname{Fpinj} A, and D(FpinjA)\mathbf D(\operatorname{Fpinj} A) for its derived category. If AA is coherent, also write Dpur(ModA)\mathbf D_{\mathrm{pur}}(\operatorname{Mod} A) for the pure derived category, D(FpinjA)c\mathbf D(\operatorname{Fpinj} A)^c for the compact objects, and Db(modA)\mathbf D^b(\operatorname{mod} A) for the bounded derived category of finitely presented AA-modules. The fp-injective module conjecture. For every ring AA, the composite

K(InjA)incK(FpinjA)canD(FpinjA)\mathbf K(\operatorname{Inj} A)\xrightarrow{\mathrm{inc}}\mathbf K(\operatorname{Fpinj} A)\xrightarrow{\mathrm{can}}\mathbf D(\operatorname{Fpinj} A)

is an equivalence. If AA is coherent, then D(FpinjA)\mathbf D(\operatorname{Fpinj} A) is compactly generated, and the composite

D(FpinjA)Dpur(ModA)D(ModA)\mathbf D(\operatorname{Fpinj} A)\to\mathbf D_{\mathrm{pur}}(\operatorname{Mod} A)\to\mathbf D(\operatorname{Mod} A)

induces an equivalence

D(FpinjA)cDb(modA).\mathbf D(\operatorname{Fpinj} A)^c\xrightarrow{\sim}\mathbf D^b(\operatorname{mod} A).

This conjecture extends analogous results for flat modules and predicts that injective resolutions model the derived category of fp-injective modules. Its general categorical form is stated in terms of exact functor categories, but the source provides no resolution of either formulation.

Sources & referencesView supporting material

Primary source

Henning Krause, “Approximations and adjoints in homotopy categories”, arXiv:1005.0209 (2010).

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