arXiv subjects
Publications and source records attributed to Manuel Saorin.
In the category of finitely generated modules over an artinian ring, we classify all the abelian exact subcategories closed under predecessors or, equivalently, all the split torsion pairs with torsion-free class closed under quotients.
Given a finite--dimensional monomial algebra $A$ we consider the trivial extension $TA$ and provide formulae, depending on the characteristic of the field, for the dimensions of the summands $HH_1(A)$ and $\Alt(DA)$ of the first Hochschild cohomology group $HH^1(TA)$. From these a formula for the dimension of $HH^1(TA)$ can be derived.
Suppose that $A$ is a semiprimary ring satisfying one of the two conditions: 1) its Yoneda ring is generated in finite degrees; 2) its Loewy length is less or equal than three. We prove that the global dimension of $A$ is finite if, and only if, there is a $m>0$ such that $Ext_A^n(S,S)=0$, for all simple $A$-modules $S$ and all $n\geq m$.
The two main theorems proved here are as follows: If $A$ is a finite dimensional algebra over an algebraically closed field, the identity component of the algebraic group of outer automorphisms of $A$ is invariant under derived equivalence. This invariance is obtained as a consequence of the following generalization of a result of Voigt. Namely, given an appropriate geometrization $\text{Comp}^A_{\bold d}$ of the family of finite $A$-module complexes with fixed sequence $\bold d$ of dimensions and an ``almost projective'' complex $X\in \text{Comp}^A_{\bold d}$, there exists a canonical vector space embedding $$T_{X}(\text{Comp}^A_{\bold d}) / T_{X}(G.X) \ \longrightarrow \text{Hom}_{D^b (A\text{-Mod})}(X, X[1]),$$ where $G$ is the pertinent product of general linear groups acting on $\text{Comp}^A_{\bold d}$, tangent spaces at $X$ are denoted by $T_X(-)$, and $X$ is identified with its image in the derived category $D^b (A\text{-Mod})$.