Actions of F_\infty whose II_1 factors and orbit equivalence relations have prescribed fundamental group

具有同调中特定预定挠的Etale等价关系

Etale equivalence relations with certain prescribed torsion in their homology

本文构造了极小étale等价关系，使其第零同调群同构于给定非循环简单维度群与Q/Z子群的直和，方法结合Bratteli图尾部等价与部分同胚。

Explicit examples of equivalence relations and factors with prescribed fundamental group and outer automorphism group

In this paper we give a number of explicit constructions for II$_1$ factors and II$_1$ equivalence relations that have prescribed fundamental group and outer automorphism group. We construct factors and relations that have uncountable fundamental group different from $\IRpos$. In fact, given any II$_1$ equivalence relation, we construct a II$_1$ factor with the same fundamental group. Given any locally compact unimodular second countable group $G$, our construction gives a II$_1$ equivalence relation $\RelR$ whose outer automorphism group is $G$. The same construction does not give a II$_1$ fa…

单侧拓扑马尔可夫移位连续轨道等价中的拓扑熵

Topological entropy in continuous orbit equivalence of one-sided topological Markov shifts

本文证明单侧拓扑马尔可夫移位的连续轨道等价类包含拓扑熵可任意大于或小于给定正实数的移位。

Some classifiable groupoid C*-algebras with prescribed K-theory

Given a simple, acyclic dimension group $G_{0}$ and countable, torsion-free, abelian group $G_{1}$, we construct a minimal, amenable, étale equivalence relation $R$ on a Cantor set whose associated groupoid $C^{*}$-algebra, $C^{*}(R)$, is tracially AF, and hence classifiable in the Elliott classification scheme for simple, amenable, separable $C^{*}$-algebras, and with $K_{*}(C^{*}(R)) \cong(G_{0}, G_{1})$.

Approximate unitary equivalence of homomorphisms from O_{\infty}

We prove that if two homomorphisms from O_{\infty} to a purely infinite simple C*-algebra have the same class in KK-theory, and if either both are unital or both are nonunital, then they are approximately unitarily equivalent. It follows that O_{\infty} is classifiable in the sense of Rordam. In particular, Rordam's classification theorem for direct limits of matrix algebras over even Cuntz algebras extends to direct limits involving both matrix algebras over even Cuntz algebras and corners of O_{\infty}, for which the K_0-group can be an arbitrary countable abelian group with no even torsion.

Proper asymptotic unitary equivalence in $\KK$-theory and projection lifting from the corona algebra

In this paper we generalize the notion of essential codimension of Brown, Douglas, and Fillmore using $\KK$-theory and prove a result which asserts that there is a unitary of the form `identity + compact' which gives the unitary equivalence of two projections if the `essential codimension' of two projections vanishes for certain $C\sp*$-algebras employing the proper asymptotic unitary equivalence of $\KK$-theory found by M. Dadarlat and S. Eilers. We also apply our result to study the projections in the corona algebra of $C(X)\otimes B$ where $X$ is $[0,1]$, $(-\infty, \infty)$, $[0,\infty)$, …