The Positive Mass Theorem near null infinity

Evolution of angular momentum and center of mass at null infinity

We study how conserved quantities such as angular momentum and center of mass evolve with respect to the retarded time at null infinity, which is described in terms of a Bondi-Sachs coordinate system. These evolution formulae complement the classical Bondi mass loss formula for gravitational radiation. They are further expressed in terms of the potentials of the shear and news tensors. The consequences that follow from these formulae are (1) Supertranslation invariance of the fluxes of the CWY conserved quantities. (2) A conservation law of angular momentum à la Christodoulou. (3) A duality pa…

Total mass and limits of quasi-local mass at future null infinity

An idealized observer of an astronomical event is situated at future null infinity, where light rays emitted from the source approach. Mathematically, null infinity corresponds to the portion of the spacetime boundary defined by equivalence classes of null geodesics. But what can we observe at future null infinity? In the note, we start by reviewing the description of null infinity in terms of the Bondi-Sachs coordinate system. In particular, we reformulate and extend the invariance of Bondi mass and the mass loss formula in terms of a modified mass aspect 2-form. At the end, we discuss new re…

在渐近平坦时空中的微局分析近null无穷

Microlocal analysis near null infinity in asymptotically flat spacetimes

本文提出了一种分析渐近平坦时空波方程在null无穷邻域正则性和衰减性质的新方法，并证明了相关正则性和衰减估计。

Formation of Trapped Surfaces from Past Null Infinity

In this paper, we extend the results of Klainerman and Rodnianski in \cite{KR:Trapped}, which were obtained for a finite region, by showing similar results from past null infinity. This allows us to recover and extend the results from past null infinity in the work of Christodoulou \cite{Chr:book}.

Quasi-local mass at axially symmetric null infinity

We give a brief review of the definition of the Wang-Yau quasilocal mass and discuss the evaluation of which on surfaces of unit size at null infinity of an axi-symmetric spacetime in Bondi-van der Burg-Metzner coordinates.

Quasi-local mass at null infinity in Bondi-Sachs coordinates

There are two important statements regarding the Trautman-Bondi mass at null infinity: one is the positivity, and the other is the Bondi mass loss formula, which are both global in nature. In this note, we compute the limit of the Wang-Yau quasi-local mass on unit spheres at null infinity of an asymptotically flat spacetime in the Bondi-Sachs coordinates. The quasi-local mass leads to a local description of the radiation that is purely gravitational at null infinity. In particular, the quasi-local mass is evaluated in terms of the news function of the Bondi-Sachs coordinates.

Uniqueness of the AdS Spacetime among Static Vacua with prescribed Null infinity

We prove that an $(n+1)$-dimensional spin static vacuum with negative cosmological constant whose null infinity has a boundary admitting a non-trivial Killing spinor field is the AdS spacetime. As a consequence, we generalize previous uniqueness results by X. Wang \cite{Wa2} and by Chru{ś}ciel-Herzlich \cite{CH} and introduce, for this class of spin static vacua, some Lorentzian manifolds which are prohibited as null infinities.

Spherically symmetric Einstein-scalar-field equations for wave-like decaying null infinity

We show that the spherically symmetric Einstein-scalar-field equations for wave-like decaying initial data at null infinity have unique local solutions and unique global solutions for small initial data. We also generalize Christodoulou's global generalized solutions to the wave-like decaying initial data. We emphasize that this decaying condition is sharp.

A novel notion of null infinity for c-boundaries and generalized black holes

We give new definitions of null infinity and black hole in terms of causal boundaries, applicable to any strongly causal spacetime $(M,g)$. These are meant to extend the standard ones given in terms of conformal boundaries, and use the new definitions to prove a classic result in black hole theory for this more general context: if the null infinity is regular (i.e. well behaved in a suitable sense) and $(M,g)$ obeys the null convergence condition, then any closed trapped surface in $(M,g)$ has to be inside the black hole region. As an illustration of this general construction, we apply it to t…

Conformal structures of static vacuum data

In the Cauchy problem for asymptotically flat vacuum data the solution-jets along the cylinder at space-like infinity develop in general logarithmic singularities at the critical sets at which the cylinder touches future/past null infinity. The tendency of these singularities to spread along the null generators of null infinity obstructs the development of a smooth conformal structure at null infinity. For the solution-jets arising from time reflection symmetric data to extend smoothly to the critical sets it is necessary that the Cotton tensor of the initial three-metric h satisfies a certain…

On the Penrose inequality along null hypersurfaces

The null Penrose inequality, i.e. the Penrose inequality in terms of the Bondi energy, is studied by introducing a funtional on surfaces and studying its properties along a null hypersurface $Ω$ extending to past null infinity. We prove a general Penrose-type inequality which involves the limit at infinity of the Hawking energy along a specific class of geodesic foliations called Geodesic Asymptotic Bondi (GAB), which are shown to always exist. Whenever, this foliation approaches large spheres, this inequality becomes the null Penrose inequality and we recover the results of Ludvigsen-Vickers …

Conserved quantities in general relativity -- the view from null infinity

In general relativity, an idealized distant observer is situated at future null infinity where light rays emitted from the source approach. This article concerns conserved quantities such as mass, energy-momentum, angular momentum, and center of mass at future null infinity. The classical definitions of Bondi mass at future null infinity ascertains the mass radiated away in gravitational waves distinctively. However, the same question for other conserved quantities such as angular momentum has been a subtle issue since the discovery of "supertranslation ambiguity" in the 1960's. Recently, new …

Evaluating quasilocal energy and solving optimal embedding equation at null infinity

We study the limit of quasilocal energy defined in [7] and [8] for a family of spacelike 2-surfaces approaching null infinity of an asymptotically flat spacetime. It is shown that Lorentzian symmetry is recovered and an energy-momentum 4-vector is obtained. In particular, the result is consistent with the Bondi-Sachs energy-momentum at a retarded time. The quasilocal mass in [7] and [8] is defined by minimizing quasilocal energy among admissible isometric embeddings and observers. The solvability of the Euler-Lagrange equation for this variational problem is also discussed in both the asymptot…

Asymptotic Shear and the Intrinsic Conformal Geometry of Null-Infinity

In this article we propose a new geometrization of the radiative phase space of asymptotically flat space-times: we show that the geometry induced on null-infinity by the presence of gravitational waves can be understood to be a generalisation of the tractor calculus of conformal manifolds adapted to the case of degenerate conformal metrics. It follows that the whole formalism is, by construction, manifestly conformally invariant. We first show that a choice of asymptotic shear amounts to a choice of linear differential operator of order two on the bundle of scales of null-infinity. We refer t…

Kerr扰动下零无穷远处的正则叶状结构

A canonical foliation on null infinity in perturbations of Kerr

本文基于Klainerman-Szeftel的GCM球面存在唯一性结果，在Kerr扰动下的未来零无穷远处构造正则叶状结构，使零能量、线动量、质心和角动量良定义并满足引力辐射物理定律，同时证明黑洞质心在扰动后发生大反冲。

Schwarzschild时空零无穷远附近的类空常平均曲率曲面

Spacelike CMC surfaces near null infinity of the Schwarzschild spacetime

本文受Treibergs结果启发，在Schwarzschild时空中构造了具有任意给定常平均曲率H_0的类空曲面，并证明其渐近行为由给定球面函数f及由f和H_0确定的函数ϕ、ψ控制，且在未来零无穷远附近一致Lipschitz。

Null-geodesics in complex conformal manifolds and the LeBrun correspondence

In the complex-Riemannian framework we show that a conformal manifold containing a compact, simply-connected, null-geodesic is conformally flat. In dimension 3 we use the LeBrun correspondence, that views a conformal 3-manifold as the conformal infinity of a selfdual four-manifolds. We also find a relation between the conformal invariants of the conformal infinity and its ambient.

The weak null condition and global existence using the p-weighted energy method

We prove global existence for solutions arising from small initial data for a large class of quasilinear wave equations satisfying the `weak null condition' of Lindblad and Rodnianski, significantly enlarging upon the class of equations for which global existence is known. In addition to the usual weak null condition, we require a certain hierarchical structure in the semilinear terms. Included in this class are the Einstein equations in harmonic coordinates, so a special case of our results is a new proof of the stability of Minkowski space. Our proof also applies to the coupled Einstein-Maxw…

反对光滑类光无限远的案例 I：启发式分析与反例

The Case Against Smooth Null Infinity I: Heuristics and Counter-Examples

本文通过回顾Christodoulou的论证，以标量辐射模拟引力辐射并构造球对称爱因斯坦-标量场方程解，证明光滑类光无限远无法准确捕捉引力辐射结构，其渐近展开含对数项，为非光滑性提供反例。