Extended Bloch group and the Chern-Simons class (Incomplete working version)

The Extended Bloch Group and the Cheeger-Chern-Simons Class

We present a formula for the full Cheeger-Chern-Simons class of the tautological flat complex vector bundle of rank two over BSL(2,\C^δ). Our formula improves the formula by Dupont and Zickert, where the class is only computed modulo 2-torsion.

Extended Bloch group and the Cheeger-Chern-Simons class

We define an extended Bloch group and show it is naturally isomorphic to H_3(PSL(2,C)^δ;Z). Using the Rogers dilogarithm function this leads to an exact simplicial formula for the universal Cheeger-Chern-Simons class on this homology group. It also leads to an independent proof of the analytic relationship between volume and Chern-Simons invariant of hyperbolic 3-manifolds conjectured by Neumann and Zagier [Topology 1985] and proved by Yoshida [Invent. Math. 1985] as well as effective formulae for the Chern-Simons invariant of a hyperbolic 3-manifold.

Bloch invariants of hyperbolic 3-manifolds

We define an invariant β(M) of a finite volume hyperbolic 3-manifold M in the Bloch group B(C) and show it is determined by the simplex parameters of any degree one ideal triangulation of M. β(M) lies in a subgroup of \B(\C) of finite \Q-rank determined by the invariant trace field of M. Moreover, the Chern-Simons invariant of M is determined modulo rationals by β(M). This leads to a simplicial formula and rationality results for the Chern Simons invariant which appear elsewhere. Generalizations of β(M) are also described, as well as several interesting examples. An appendix describes a scisso…

Geometric interpretation of simplicial formulas for the Chern-Simons invariant

We give a direct interpretation of Neumann's combinatorial formula for the Chern-Simons invariant of a 3-manifold with a representation in PSL(2,C) whose restriction to the boundary takes values in upper triangular matrices. Our construction does not involve group homology or Bloch group but is based on the construction of an explicit flat connection for each tetrahedron of a simplicial decomposition of the manifold.

双曲3-流形、Bloch群与Walter Neumann的工作

Hyperbolic 3-manifolds, the Bloch group, and the work of Walter Neumann

本文综述Walter Neumann关于双曲3-流形理想三角剖分、体积、Chern–Simons不变量及Bloch群元素的研究，并阐明其对量子拓扑与数学物理的影响。

Fundamental classes of 3-manifold group representations in SL(4,R)

We compute the fundamental class (in the extended Bloch group) for representations of fundamental groups of 3-manifolds to SL(4,R) that factor over SL(2,C), in particular for those factoring over the isomorphism PSL(2,C) = S0(3,1). We also discuss consequences for the number of connected components of SL(4,R)-character varieties, and we show that there are knots with arbitrarily many components of vanishing Chern-Simons invariant in their SL(n,C)-character varieties