Search arXiv⌕ Search

arXiv · 0709.3660

Einstein's equations and the embedding of 3-dimensional CR manifolds

Abstract

We prove several theorems concerning the connection between the local CR embeddability of 3-dimensional CR manifolds, and the existence of algebraically special Maxwell and gravitational fields. We reduce the Einstein equations for spacetimes associated with such fields to a system of CR invariant equations on a 3-dimensional CR manifold defined by the fields. Using the reduced Einstein equations we construct two independent CR functions for the corresponding CR manifold. We also point out that the Einstein equations, imposed on spacetimes associated with a 3-dimensional CR manifold, imply that the spacetime metric, after an appropriate rescaling, becomes well defined on a circle bundle over the CR manifold. The circle bundle itself emerges as a consequence of Einstein's equations.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

C. Denson Hill, Jerzy Lewandowski, Pawel Nurowski. 2008-05-22. Einstein's equations and the embedding of 3-dimensional CR manifolds. https://arxiv.org/abs/0709.3660

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

A duality theorem for a four dimensional Willmore energy

We prove an analogue of the energy identities underlying Bryant's duality theorem for a four-dimensional Willmore energy $\mathcal{E}_{\rm GR}$ obtained by Graham--Reichert and Zhang in codimension one. We show that, for an immersion $Φ$ of a compact four-dimensional manifold without boundary $Σ$ into $\mathbb{R}^5$, the energy $\mathcal{E}_{\rm GR}(Φ)$ is equal to two energies associated with its conformal Gauss map $Y$: one defined only in terms of the image of $Y$, which is the analogue of the area functional for Willmore surfaces, and another defined on maps from $Σ$ into the de Sitter space $\mathbb{S}^{5,1}$, which is the analogue of the Dirichlet energy for Willmore surfaces. We prove that, even when restricted to immersions of a given topological manifold $Σ^4$, $\mathcal{E}_{\rm GR}$ is not bounded below on the set of immersions from $Σ$ into $\mathbb{R}^5$. We exhibit a second conformally invariant energy $\mathcal{E}_{\rm P}$ that is bounded below and whose construction is closer to that of the two-dimensional Willmore energy.

math.DG↗

Barycentric subspace analysis of network-valued data

Certain data are naturally modeled by networks or weighted graphs, be they biological networks or mobility networks. When there is no canonical labeling of the nodes across the dataset, we talk about unlabeled networks. In this paper, we focus on the question of exploratory analysis of this type of data. More specifically, we address the issue of interpreting the feature subspace constructed by dimensionality reduction methods. Most existing methods for network-valued data are derived from principal component analysis (PCA) and therefore rely on subspaces generated by a set of vectors, which we identify as a major limitation in terms of interpretability. Instead, we propose to implement the method called barycentric subspace analysis (BSA), which relies on subspaces generated by a set of points, which we choose, in practice, to be samples. In order to provide a computationally feasible framework for BSA, we introduce a novel embedding for unlabeled networks where we replace their usual representation by equivalence classes of isomorphic networks with that by equivalence classes of cospectral networks. In a simulated study, we demonstrate the improved interpretability of BSA compared to tangent PCA. We then illustrate through two real-world datasets how BSA can be used both to visualize known patterns and to discover new ones in network-valued distributions.

math.DG↗

Isoparametric Hypersurfaces in Products of Simply Connected Space Forms

For $i\in\{1,2\}, $ let $\mathbb Q_{ε_i}^{n_i}$ denote the simply connected space form of dimension $n_i\ge 2$ and constant sectional curvature $ε_i\in\mathbb R$, $(ε_1,ε_2)\ne (0,0)$. We prove that any connected isoparametric hypersurface of $\mathbb Q_{ε_1}^{n_1}\times\mathbb Q_{ε_2}^{n_2}$ has constant angle function. We use this property to classify both the isoparametric and homogeneous hypersurfaces of $\mathbb Q_{ε_1}^{n_1}\times\mathbb Q_{ε_2}^{n_2}$ when $ε_1ε_2\le 0$. Under additional hypotheses, we obtain a similar classification result in the case $ε_1ε_2>0$.

math.DG↗