Signatures and Higher Signatures of $S^1$-Quotients

Compact Clifford-Klein forms of symmetric spaces -- revisited

This article discusses the existence problem of a compact quotient of a symmetric space by a properly discontinuous group with emphasis on the non-Riemannian case. Discontinuous groups are not always abundant in a homogeneous space $G/H$ if $H$ is non-compact. The first half of the article elucidates general machinery to study discontinuous groups for $G/H$, followed by the most update and complete list of symmetric spaces with/without compact quotients. In the second half, as applications of general theory, we prove: (i) there exists a 15 dimensional compact pseudo-Riemannian manifold of sign…

The Spectral Geometry of the Riemann Curvature Operator in the Higher Signature Setting

We study the spectral geometry of the Riemann curvature tensor for Pseudo-Riemannian manifolds and provide some examples illustrating the phenomena which can arise in the higher signature setting. Dedication: This paper is dedicated to the memory of our colleague Prof.G. Tsagas who studied the spectral geometry of Laplacian.

Spacelike Jordan Osserman algebraic curvature tensors in the higher signature setting

Let $R$ be an algebraic curvature tensor on a vector space of signature $(p,q)$ defining a spacelike Jordan Osserman Jacobi operator $\JJ_R$. We show that the eigenvalues of $\JJ_R$ are real and that $\JJ_R$ is diagonalizable if $p<q$.

Vectors of Higher Rank on a Hadamard Manifold with Compact Quotient

<ENGLISH> Consider a closed, smooth manifold M of nonpositive sectional curvature. Write p:UM-> M for the unit tangent bundle over M and let R_> denote the subset consisting of all vectors of higher rank. This subset is closed and invariant under the geodesic flow on UM. We will define the structured dimension sdim(R_>) which, essentially, is the dimension of the set p(R_>) of base points of R_>. The main result holds for manifolds with sdim(R_>) < dim(M)/2: For every E>0 there is an E-dense, flow invariant, closed subset Z_E in UM R_> such that p(Z_E)=M. For every point in M this means that t…

The Twisted Higher Harmonic Signature for Foliations

We prove that the higher harmonic signature of an even dimensional oriented Riemannian foliation of a compact Riemannian manifold with coefficients in a leafwise U(p,q)-flat complex bundle is a leafwise homotopy invariant. We also prove the leafwise homotopy invariance of the twisted higher Betti classes. Consequences for the Novikov conjecture for foliations and for groups are investigated. Replaces The Higher Harmonic Signature for Foliations I: The Untwisted Case, and contains significant improvements.

C*-Algebraic higher Signature on Non-Witt space

Signature plays an important role in geometry and topology. In the space with singularity, Goresky and MacPherson extend the signatures to oriented pseudomanifolds with only even codimensional stratums by using generalized Poincare duality of intersection homology. After that Siegel extended the signature on Witt spaces. Higson and Xie study the $C^*$- higher signature on Witt space. Followed by the combinatorial framework developed by Higson and Roe, this paper construct the $C^*$-signature on non Witt space with noncommutative geometric methods. In conical singular case, we compare analytica…

Product formula for Atiyah-Patodi-Singer index classes and higher signatures

We define generalized Atiyah-Patodi-Singer boundary conditions of product type for Dirac operators associated to C*-vector bundles on the product of a compact manifold with boundary and a closed manifold. We prove a product formula for the K-theoretic index classes, which we use to generalize the product formula for the topological signature to higher signatures.

Elliptic Operators and Higher Signatures

Building on the theory of elliptic operators, we give a unified treatment of the following topics: - the problem of homotopy invariance of Novikov's higher signatures on closed manifolds; - the problem of cut-and-paste invariance of Novikov's higher signatures on closed manifolds; - the problem of defining higher signatures on manifolds with boundary and proving their homotopy invariance.

椭圆算子高阶rho不变量的函子性

Functoriality for higher rho invariants of elliptic operators

本文通过有限传播论证证明了具有正数量曲率的闭spin流形上Dirac算子的高阶rho不变量在Galois覆盖商映射下具有函子性，并应用于相关不变量的计算。

Hyperkahler quotients and algebraic curves

We develop a graphical representation of polynomial invariants of unitary gauge groups, and use it to find the algebraic curve corresponding to a hyperkahler quotient of a linear space. We apply this method to four dimensional ALE spaces, and for the A_k, D_k, and E_6 cases, derive the explicit relation between the deformations of the curves away from the orbifold limit and the Fayet-Iliopoulos parameters in the corresponding quotient construction. We work out the orbifold limit of E_7, E_8, and some higher dimensional examples.

紧致商的齐性空间与球丛的同伦理论

Compact quotients of homogeneous spaces and homotopy theory of sphere bundles

本文研究了可约齐性空间的紧致商问题，证明了相关球丛的同伦性质，并推翻了一些经典猜想。

The signature package on Witt spaces, II. Higher signatures

This is a sequel to the paper "The signature package on Witt spaces, I. Index classes" by the same authors. In the first part we investigated, via a parametrix construction, the regularity properties of the signature operator on a stratified Witt pseudomanifold, proving, in particular, that one can define a K-homology signature class. We also established the existence of an analytic index class for the signature operator twisted by a C^*_rΓMischenko bundle and proved that the K-homology signature class is mapped to the signature index class by the assembly map. In this paper we continue our st…

通过高步次子黎曼结构中的商导致测度收缩性质失效

Failure of the measure contraction property via quotients in higher-step sub-Riemannian structures

本文利用等距群作用商下局部 MCP 的稳定性结果，证明高步次子黎曼结构乃至理想结构可违反测度收缩性质，并回答相关公开问题。

高签名下的全局超曲性

Global hyperbolicity in higher signatures

本文研究了高签名下伪黎曼流形的全局超曲性，推广了该概念并证明了因果钻石的紧致性，同时推导了Plateau问题解的存在性及GH-正则表示的特征化。

The Spectral Flow of the Odd Signature operator and Higher Massey Products

We show how to compute the spectral flow of the odd signature operator $\pm *d_{a_t}-d_{a_t}*$ along an analytic path of flat connections $a_t$ on a bundle over a closed odd-dimensional manifold in terms of Massey products in the DGLA of bundle-valued differential forms. To obtain this information, we set up a sequence of cochain complexes $\{\calg^*_n,δ_n\}$, for $n=0,1,2,\ldots$ and Hermitian forms $$Q_n:\calg_n\times\calg_n\ra \bbbC$$ whose signatures determine the spectral flow through $t=0$. The complexes and Hermitian forms are constructed using Massey products.

The quotient girth of normed spaces, and an extension of Schäffer's dual girth conjecture to Grassmannians

In this note we introduce a natural Finsler structure on convex surfaces, referred to as the projective Finsler structure, which is dual in a sense to the obvious inclusion of a convex surface in a normed space. It has an associated projective girth, which is similar to the notion of girth defined by Schäffer. We prove the analogs of Schäffer's dual girth conjecture (proved by Álvarez-Paiva) and the Holmes-Thompson dual volumes theorem in the projective setting. We then show that the projective Finsler structure admits a natural extension to higher Grassmannians, and prove the corresponding th…

Higher signature Delaunay decompositions

A Delaunay decomposition is a cell decomposition in R^d for which each cell is inscribed in a Euclidean ball which is empty of all other vertices. This article introduces a generalization of the Delaunay decomposition in which the Euclidean balls in the empty ball condition are replaced by other families of regions bounded by certain quadratic hypersurfaces. This generalized notion is adaptable to geometric contexts in which the natural space from which the point set is sampled is not Euclidean, but rather some other flat semi-Riemannian geometry, possibly with degenerate directions. We prove …