We give an interpretation of the $(q,t)$-deformed Cartan matrices of finite type and their inverses in terms of bigraded modules over the generalized preprojective algebras of Langlands dual type in the sense of Geiss-Leclerc-Schr{o}er~[Invent.~math.
~{bf{209}} (2017)]. As an application, we compute the first extension groups between the generic kernels introduced by Hernandez-Leclerc~[J.~Eur.~Math.~Soc.~{bf 18} (2016)], and propose a conjecture that their dimensions coincide with the pole orders of the normalized $R$-matrices between the corresponding Kirillov-Reshetikhin modules.
Geiss-Leclerc-Schroer [Invent. Math. 209 (2017)] has introduced a notion of generalized preprojective algebra associated with a generalized Cartan matrix and its symmetrizer. This class of algebra realizes a crystal structure on the set of maximal di
mensional irreducible components of the nilpotent variety [Selecta Math. (N.S.) 24 (2018)]. For general finite types, we give stratifications of these components via partial orders of torsion classes in module categories of generalized preprojective algebras in terms of Weyl groups. In addition, we realize Mirkovic-Vilonen polytopes from generic modules of these components, and give a identification as crystals between the set of Mirkovic-Vilonen polytopes and the set of maximal dimensional irreducible components except for type $mathsf{G}_2$. This generalizes results of Baumann-Kamnitzer [Represent. Theory 16 (2012)] and Baumann-Kamnitzer-Tingley [Publ. Math. Inst. Hautes Etudes Sci. 120 (2014)].
For a symmetrizable GCM $C$ and its symmetrizer $D$, Geiss-Leclerc-Schroer [Invent. Math. 209 (2017)] has introduced a generalized preprojective algebra $Pi$ associated to $C$ and $D$, that contains a class of modules, called locally free modules. We
show that any basic support $tau$-tilting $Pi$-module is locally free and gives a classification theorem of torsion-free classes in $operatorname{mathbf{rep}}{Pi}$ as the generalization of the work of Mizuno [Math. Z. 277 (2014)].
