Self-Orthogonal $\tau$-Tilting Modules and Tilting Modules II: Annihilator Separation

Abstract

Let $A$ be an Artin algebra and let $T$ be a self-orthogonal $\tau$-tilting right $A$-module. Set $I=\Ann_A(T)$. We prove that \[ \Hom_A(I,T)=0=\Ext_A^n(I,T)\qquad(n\geq 1). \] It follows that the torsion class generated by $I$ is Hom-orthogonal to $\Sub T$. This separation yields faithfulness criteria expressed through ideal tops, socles, and projective supports. We also prove a finitistic-dimension obstruction: if $B=\End_A(T)^{\rm op}$ has finite little finitistic dimension, then $\Fac T\cap{}^{\perp_{\geq0}}T=\{0\}$. As an application, the self-orthogonal $\tau$-tilting conjecture holds for radical square zero Artin algebras. Finally, the support criteria apply to semisimple-source triangular matrix algebras with arbitrary local terminal blocks.