In this paper we define the notion of ampleness for two-sided tilting complexes over finite dimensional algebras and prove its basic properties.We call a finite dimensional k-algebra A of finite global dimension Fano if (A * [−d]) −1 is ample for some d ≥ 0. For example geometric algebras in the sense of Bondal-Polishchuk are Fano. We give a characterization of representation type of a quiver from a noncommutative algebro-geometric view point, that is, a finite acyclic quiver has finite representation type if and only if its path algebra is fractional Calabi-Yau, and a finite acyclic quiver has infinite representation type if and only if its path algebra is Fano.
IntroductionLet X be a nonsingular projective variety over a field k and let ω X be its canonical bundle. Then the functor. By this fact, from a noncommutative (or categorical) algebro-geometric view point, one thinks of a triangulated category T as the derived category of coherent sheaves of some "space" X and of the Serre functor S T of T (if exists) as the derived tensor product of " dim X"-shifted "canonical bundle" ω X . From this view point, the notion of Calabi-Yau algebra ( and Calabi-Yau category ) is defined and studied extensively by many researchers.In this paper we introduce the notion of ampleness for two-sided tilting complexes over finite dimensional k-algebras. Let A be a finite dimensional k-algebra of finite global dimension.
Definition 0.1 (Definition 2.6). A two-sided tilting complex σ over A is called very ample if Hi (σ) = 0 for i ≥ 1 and σ n is pure for n 0. σ is called ample if σ n is pure for n 0.In Section 2, we justify this definition by using the theory of noncommutative projective schemes due to Artin-Zhang [AZ] and Polishchuk [Po]. In the theory of noncommutative projective schemes , for a graded coherent ring R over k we attach an imaginary geometric object proj R = ( cohproj R, R, (1) ) . An abelian category cohproj R is considered as the category of coherent sheaves on proj R. (See Section 1.) In Section 2 we show that the following facts hold. If σ is a very ample tilting complex over A, then the tensor algebra T := T A (H 0 (σ)) of H 0 (σ) over A is a graded connected coherent ring over A and there is a t-structure D σ defined by σ in Perf A and its heart H σ is equivalent to cohproj T . Moreover the following Theorem holds. where T := T A (H 0 (σ)) is the tensor algebra of H 0 (σ) over A.