On single commutators in II_1-factors

Sums of commutators in ideals and modules of type II factors

Let M be a factor of type II_\infty or II_1 having separable predual and let M-bar be the algebra of affiliated τ-measureable operators. We characterize the commutator space [I,J] for sub-(M,M)-bimodules I and J of M-bar.

Abelian self-commutators in finite factors

An abelian self-commutator in a C*-algebra $\mathcal{A}$ is an element $A$ that can be written as $A=X^*X-XX^*$, with $X\in\mathcal{A}$ such that $X^*X$ and $XX^*$ commute. It is shown that, given a finite AW*-factor $\mathcal{A}$, there exists another finite AW*-factor $\mathcal{M}$ of same type as $\mathcal{A}$, that contains $\mathcal{A}$ as an AW*-subfactor, such that any self-adjoint element $X\in\mathcal{M}$ of quasitrace zero is an abelian self-commutator in $\mathcal{M}$.

Nilpotent elements of operator ideals as single commutators

For an arbitrary operator ideal I, every nilpotent element of I is a single commutator of operators from I^t, for an exponent t that depends on the degree of nilpotency.

Commutator estimates in $W^*$-factors

Let $\mathcal{M}$ be a $W^*$-factor and let $S\left( \mathcal{M} \right) $ be the space of all measurable operators affiliated with $\mathcal{M}$. It is shown that for any self-adjoint element $a\in S(\mathcal{M})$ there exists a scalar $λ_0\in\mathbb{R}$, such that for all $\varepsilon > 0$, there exists a unitary element $u_\varepsilon$ from $\mathcal{M}$, satisfying $|[a,u_\varepsilon]| \geq (1-\varepsilon)|a-λ_0\mathbf{1}|$. A corollary of this result is that for any derivation $δ$ on $\mathcal{M}$ with the range in an ideal $I\subseteq\mathcal{M}$, the derivation $δ$ is inner, that is $δ(…

UHF代数中的交换子

Single commutators in $C^*$-algebras

本文证明在UHF代数中，迹为零的元素均可表示为单个交换子，即核等于所有交换子集合。

由因子映射和子群胚产生的拓扑全群的最大子群

Maximal subgroups of topological full groups arising from factor maps and subgroupoids

本文通过因子映射和宽开子群胚构造拓扑全群及其换位子群的最大子群，给出最大性判据，并应用于康托尔极小系统，产生 Grigorchuk-Vorobets 猜想中的划分稳定化子及顺从群中的最大子群例子。