Strongly tilting truncated path algebras

For any truncated path algebra $Λ$, we give a structural description of the modules in the categories ${\cal P}^{<\infty}(Λ\text{-mod})$ and ${\cal P}^{<\infty}(Λ\text{-Mod})$, consisting of the finitely generated (resp. arbitrary) $Λ$-modules of finite projective dimension. We deduce that these categories are contravariantly finite in $Λ\text{-mod}$ and $Λ\text{-Mod}$, respectively, and determine the corresponding minimal ${\cal P}^{<\infty}$-approximation of an arbitrary $Λ$-module from a projective presentation. In particular, we explicitly construct - based on the Gabriel quiver $Q$ and the Loewy length of $Λ$ - the basic strong tilting module $_ΛT$ (in the sense of Auslander and Reiten) which is coupled with ${\cal P}^{<\infty}(Λ\text{-mod})$ in the contravariantly finite case. A main topic is the study of the homological properties of the corresponding tilted algebra $\tildeΛ = \text{End}_Λ(T)^{\text{op}}$, such as its finitistic dimensions and the structure of its modules of finite projective dimension. In particular, we characterize, in terms of a straightforward condition on $Q$, the situation where the tilting module $T_{\tildeΛ}$ is strong over $\tildeΛ$ as well. In this $Λ$-$\tildeΛ$-symmetric situation, we obtain sharp results on the submodule lattices of the objects in ${\cal P}^{<\infty}(\text{Mod-}\tildeΛ)$, among them a certain heredity property; it entails that any module in ${\cal P}^{<\infty}(\text{Mod-}\tildeΛ)$ is an extension of a projective module by a module all of whose simple composition factors belong to ${\cal P}^{<\infty}(\text{mod-}\tildeΛ)$.

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