Rigidity results for certain 3-dimensional singular spaces and their fundamental groups

Diagram rigidity for geometric amalgamations of free groups

We prove a topological rigidity result for simple, thick, hyperbolic P-manifolds of dimension 2: isomorphism of the fundamental groups implies homeomorphism of the P-manifolds. An immediate application is a diagram rigidity theorem for certain amalgamations of free groups: the direct limits of two such diagrams are isomorphic if and only if there is an isomorphism between the respective diagrams.

Absolute profinite rigidity of some closed fibered hyperbolic 3-manifolds

We give the first examples of closed fibered hyperbolic 3-manifolds whose fundamental groups are distinguished from every other finitely generated, residually finite group by their finite quotients. One of the examples is also the first example of a non-orientable profinitely rigid hyperbolic 3-manifold.

Patterson-Sullivan系统刚性及其在随机游走和熵刚性中的应用

Rigidity for Patterson--Sullivan systems with applications to random walks and entropy rigidity

本文引入Patterson-Sullivan系统，研究其在随机游走和熵刚性中的应用，证明了Tukia的测度边界刚性定理的推广，并探讨了Patterson-Sullivan测度的奇异性猜想。

Quasi-isometric rigidity of piecewise geometric manifolds

Two groups are virtually isomorphic if they can be obtained one from the other via a finite number of steps, where each step consists in taking a finite extension or a finite index subgroup (or viceversa). Virtually isomorphic groups are always quasi-isometric, and a group G is quasi-isometrically rigid if every group quasi-isometric to G is virtually isomorphic to G. In this survey we describe quasi-isometric rigidity results for fundamental groups of manifolds which can be decomposed into geometric pieces. After stating by now classical results on lattices in semisimple Lie groups, we focus …

3-流形中的投射有限几乎刚性

Profinite almost rigidity in 3-manifolds

该研究证明带空或环面边界的紧致可定向3-流形具投射有限几乎刚性，结合外围结构可唯一确定混合3-流形Seifert部分同胚类型，否则无法唯一确定，证明基于JSJ分解。

Rigidity of warped cones and coarse geometry of expanders

We study the geometry of warped cones over free, minimal isometric group actions and related constructions of expander graphs. We prove a rigidity theorem for the coarse geometry of such warped cones: Namely, if a group has no abelian factors, then two such warped cones are quasi-isometric if and only if the actions are finite covers of conjugate actions. As a consequence, we produce continuous families of non-quasi-isometric expanders and superexpanders. The proof relies on the use of coarse topology for warped cones, such as a computation of their coarse fundamental groups.

Profinite刚性及圆周上的双曲四穿孔球丛

Profinite rigidity and hyperbolic four-punctured sphere bundles over the circle

本文证明了圆周上的双曲四穿孔球丛可由其基本群的有限商群在所有3-流形群中被唯一区分，并通过改进Liu的结果证明了纤维拓扑类型可由profinite完备性检测。

Rigidity for von Neumann algebras and their invariants

We give a survey of recent classification results for crossed product von Neumann algebras arising from measure preserving group actions on probability spaces. This includes II_1 factors with uncountable fundamental groups and the construction of W*-superrigid actions where the crossed product entirely remembers the initial group action that it was constructed from.

Rigidity results for Bernoulli actions and their von Neumann algebras (after Sorin Popa)

We survey Sorin Popa's recent work on Bernoulli actions. The paper was written on the occasion of the Bourbaki seminar. Using very original methods from operator algebras, Sorin Popa has shown that the orbit structure of the Bernoulli action of a property (T) group, completely remembers the group and the action. This information is even essentially contained in the crossed product von Neumann algebra, yielding the first von Neumann strong rigidity theorem in the literature. The same methods allow Popa to obtain II_1 factors with prescribed countable fundamental group.

Profinite rigidity in the SnapPea census

A well-known question asks whether any two non-isometric finite volume hyperbolic 3-manifolds are distinguished from each other by the finite quotients of their fundamental groups. At present, this has been proved only when one of the manifolds is a once-punctured torus bundle over the circle. We give substantial computational evidence in support of a positive answer, by showing that no two manifolds in the SnapPea census of 72 942 finite volume hyperbolic 3-manifolds have the same finite quotients.