Extension algebras of standard modules

Abstract

Let $A$ be a finite dimensional $k$-algebra standardly stratified for a partial order $\leqslant$ and $Δ$ be the direct sum of all standard modules. In this paper we study the extension algebra $E= \text{Ext}_A^{\ast} (Δ, Δ)$ of standard modules, characterize the stratification property of $E$ for $\leqslant$ and $\leqslant ^{op}$, and obtain a sufficient condition for $E$ to be a generalized Koszul algebra (in a sense which we define).

The final version accepted by Comm. Algebra