Selfextensions of modules for Nakayama and Brauer tree algebras

Abstract

For Nakayama algebras $A$, we prove that in case $Ext_A^1(M,M) \neq 0$ for an indecomposable $A$-module $M$, we have that the projective dimension of $M$ is infinite. As an application we give a new proof of a classical result from \cite{Gus} on bounds of the Loewy length for Nakayama algebras with finite global dimension. For Brauer tree algebras $A$ with an indecomposable module $M$, we prove that $Ext_A^1(M,M) \neq 0$ implies $Ext_A^i(M,M) \neq 0$ for all $i>0$.