The Auslander-Gruson-Jensen Recollement

TL;DR

This paper studies the Auslander-Gruson-Jensen functor, showing it has fully faithful adjoints and forms a recollement that reveals its nature as a Serre localization, connecting module and functor categories.

Contribution

It establishes the existence of fully faithful adjoints to the Auslander-Gruson-Jensen functor and characterizes it as a Serre localization, extending its duality properties.

Findings

The functor admits fully faithful left and right adjoints.

It induces an equivalence of categories modulo a Serre subcategory.

The functor acts as a Serre localization functor.

Abstract

For any ring $R$, the Auslander-Gruson-Jensen functor is the exact contravariant functor $$\textsf{D}_A:\textsf{fp}(\textsf{Mod}(R),\textsf{Ab})\longrightarrow(\textsf{mod}(R^{op}),\textsf{Ab})$$ sending representable functors $(X,\hspace{0.05cm}\underline{\ \ }\hspace{0.1cm} )$ to tensor functors $X\otimes\hspace{0.05cm}\underline{\ \ }\hspace{0.1cm} $. We show that this functor admits a fully faithful left adjoint $\textsf{D}_L$ and a fully faithful right adjoint $\textsf{D}_R$. The left adjoint $$\textsf{D}_L\:(\textsf{mod}(R^{op}),\textsf{Ab})\longrightarrow \textsf{fp}(\textsf{Mod}(R),\textsf{Ab})$$ induces an equivalence of categories $$\frac{\textsf{fp}(\textsf{Mod}(R),\textsf{Ab})}{\{F\ |\ \textsf{D}_A F=0\}}\cong(\textsf{mod}(R^{op}),\textsf{Ab})^{op}$$ where $\{F \ |\ \textsf{D}_A F=0\}$ is the Serre subcategory of $\textsf{fp}(\textsf{Mod}(R),\textsf{Ab})$ consisting of all functors $F$ arising from pure exact sequences. As a result, the functor $\textsf{D}_A$ is seen to be a Serre localization functor. The right adjoint $$\textsf{D}_R:(\textsf{mod}(R^{op}),\textsf{Ab})\longrightarrow \textsf{fp}(\textsf{Mod}(R),\textsf{Ab})$$ together with $\textsf{D}_A$ restricts to the well known Auslander-Gruson-Jensen duality.