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arXiv 0902.0024math.OA
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图秩为1的单C* 代数中的酉

Unitaries in a Simple C*-algebra of Tracial Rank One

Huaxin Lin

摘要:

设$A$是一个迹秩不大于1的单无穷维\CA,其迹状态空间为$T(A)$,$U(A)$是$A.$的酉群,且$u\in U_0(A),$是$U(A)$的含有单位元的连通分支.证明了对任意的$\ep>0,$,存在一个自伴元$h\in A_{s.a}$,使得$$ \|u-\exp(ih)\|<\ep. $$.并研究了当$u$可以用有限谱$A$中的酉逼近时的问题.用$CU(A)$表示$U(A)$的酉群的子群由其分解子生成的闭包。本文证明了$CU(A)\subset U_0(A).$可以用有限谱的酉来逼近当且仅当对所有的$n\ge 1.$都有$u\in CU(A)$和$\widehat{u^n+(u^n)^*},i(\widehat{u^n-(u^n)^*})\in \overline{ρ_A(K_0(A)}$.并举例说明了$CU(A)$中存在不能用有限谱的酉来逼近的酉.值得注意的是,这些结果是在缺乏顺从性的情况下获得的。

英文摘要:

Let $A$ be a unital separable simple infinite dimensional \CA with tracial rank no more than one and with the tracial state space $T(A)$ and let $U(A)$ be the unitary group of $A.$ Suppose that $u\in U_0(A),$ the connected component of $U(A)$ containing the identity. We show that, for any $\ep>0,$ there exists a selfadjoint element $h\in A_{s.a}$ such that $$ \|u-\exp(ih)\|<\ep. $$ We also study the problem when $u$ can be approximated by unitaries in $A$ with finite spectrum. Denote by $CU(A)$ the closure of the subgroup of unitary group of $U(A)$ generated by its commutators. It is known that $CU(A)\subset U_0(A).$ Denote by $\widehat{a}$ the affine function on $T(A)$ defined by $\widehat{a}(τ)=τ(a).$ We show that $u$ can be approximated by unitaries in $A$ with finite spectrum if and only if $u\in CU(A)$ and $\widehat{u^n+(u^n)^*},i(\widehat{u^n-(u^n)^*})\in \overline{ρ_A(K_0(A)}$ for all $n\ge 1.$ Examples are given that there are unitaries in $CU(A)$ which can not be approximated by unitaries with finite spectrum. Significantly these results are obtained in the absence of amenability.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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