Preprojective Modules and Auslander-Reiten Components

Abstract

Auslander and Smalø (Auslander, M., Smalø, S. O. (1980). Preprojective modules over artin algebras. J. Algebra 66:61–122) introduced and studied extensively preprojective modules and preinjective modules over an artin algebra. We now call a module hereditarily preprojective or hereditarily preinjective if its submodules are all preprojective or its quotient modules are all preinjective, respectively. Coelho (Coelho, F. U. (1993). Components of Auslander-Reiten quivers with only preprojective modules. J. Algebra 157: 472–488) studied Auslander-Reiten components containing only hereditarily preprojective modules and gave a number of characterizations of such components. We shall study further these modules by using the description of shapes of semi-stable Auslander-Reitan components; see Liu (Liu, S. (1992). Degrees of irreducible maps and the shapes of Auslander-Reiten quivers. J. London Math. Soc. 45(2):32–54; Liu, S. (1993). Semi-stable components of an Auslander-Reiten quiver. J. London Math. Soc. 47(2):405–416). Our results will imply the result of Coelho (Coelho, F. U. (1993). Components of Auslander-Reiten quivers with only preprojective modules. J. Algebra 157: 472–488, (1.2)) and that of Auslander-Smalø (Auslander, M. and Smalø, S. O. (1980). Preprojective modules over artin algebras, J. Algebra 66:61–122, (9.16)). As an application, moreover, we shall show that a stable Auslander-Reiten component with “few” stable maps in TrD-direction is of shape ℤA ∞.