Classification of Finite Potent Endomorphisms

Sums of two square-zero selfadjoint or skew-selfadjoint endomorphisms

Let $V$ be a finite-dimensional vector space over a field $\mathbb{F}$, equipped with a symmetric or alternating non-degenerate bilinear form $b$. When the characteristic of $\mathbb{F}$ is not $2$, we characterize the endomorphisms $u$ of $V$ that split into $u=a_1+a_2$ for some pair $(a_1,a_2)$ of $b$-selfadjoint (respectively, $b$-skew-selfadjoint) endomorphisms of $V$ such that $(a_1)^2=(a_2)^2=0$. In the characteristic $2$ case, we obtain a similar classification for the endomorphisms of $V$ that split into the sum of two square-zero $b$-alternating endomorphisms of $V$ when $b$ is altern…

Sums and products of two quadratic endomorphisms of a countable-dimensional vector space

Let $V$ be a vector space with countable dimension over a field, and let $u$ be an endomorphism of it which is locally finite, i.e. $(u^k(x))_{k \geq 0}$ is linearly dependent for all $x$ in $V$. We give several necessary and sufficient conditions for the decomposability of $u$ into the sum of two square-zero endomorphisms. Moreover, if $u$ is invertible, we give necessary and sufficient conditions for the decomposability of $u$ into the product of two involutions, as well as for the decomposability of $u$ into the product of two unipotent endomorphisms of index $2$. Our results essentially ex…

Endomorphism rings of finite global dimension

For a commutative local ring $R$, consider (noncommutative) $R$-algebras $Λ$ of the form $Λ= End_R(M)$ where $M$ is a reflexive $R$-module with nonzero free direct summand. Such algebras $Λ$ of finite global dimension can be viewed as potential substitutes for, or analogues of, a resolution of singularities of $Spec R$. For example, Van den Bergh has shown that a three-dimensional Gorenstein normal $C$-algebra with isolated terminal singularities has a crepant resolution of singularities if and only if it has such an algebra $Λ$ with finite global dimension and which is maximal Cohen--Macaulay…

Algebras of finite representation type arising from maximal rigid objects

We give a complete classification of all algebras appearing as endomorphism algebras of maximal rigid objects in standard 2-Calabi-Yau categories of finite type. Such categories are equivalent to certain orbit categories of derived categories of Dynkin algebras. It turns out that with one exception, all the algebras that occur are $2$-Calabi-Yau-tilted, and therefore appear in an earlier classification by Bertani-Økland and Oppermann. We explain this phenomenon by investigating the subcategories generated by rigid objects in standard 2-Calabi-Yau categories of finite type.

曲线上向量场的李子代数

Lie subalgebras of vector fields on curves

研究光滑仿射曲线上Krichever-Novikov代数的子代数结构，证明每个无限维子代数同构于另一个Krichever-Novikov代数的有限余维子代数，并给出通用包络代数非诺特性、Dixmier性质及Witt代数无限维子代数分类等应用。