A pairing in homology and the category of linear complexes of tilting modules for a quasi-hereditary algebra

Abstract

We show that there exists a natural non-degenerate pairing of the homomorphism space between two neighbor standard modules over a quasi-hereditary algebra with the first extension space between the corresponding costandard modules and vise versa. Investigation of this phenomenon leads to a family of pairings involving standard, costandard and tilting modules. In the graded case, under some "Koszul-like" assumptions (which we prove are satisfied for example for the blocks of the category $\mathcal{O}$), we obtain a non-degenerate pairing between certain graded homomorphism and graded extension spaces. This motivates the study of the category of linear tilting complexes for graded quasi-hereditary algebras. We show that, under assumptions, similar to those mentioned above, this category realizes the module category for the Koszul dual of the Ringel dual of the original algebra. As a corollary we obtain that under these assumptions the Ringel and Koszul dualities commute.