We study the initial value problem for the conformal field equations with data given on a cone ${\cal N}_p$ with vertex $p$ so that in a suitable conformal extension the point $p$ will represent past time-like infinity $i^-$, the set ${\cal N}_p \setminus \{p\}$ will represent past null infinity ${\cal J}^-$, and the freely prescribed (suitably smooth) data will acquire the meaning of the incoming {\it radiation field} for the prospective vacuum space-time. It is shown that: (i) On some coordinate neighbourhood of $p$ there exist smooth fields which satisfy the conformal vacuum field equations and induce the given data at all orders at $p$. The Taylor coefficients of these fields at $p$ are uniquely determined by the free data. (ii) On ${\cal N}_p$ there exists a unique set of fields which induce the given free data and satisfy the transport equations and the inner constraints induced on ${\cal N}_p$ by the conformal field equations. These fields and the fields which are obtained by restricting the functions considered in (i) to ${\cal N}_p$ coincide at all orders at $p$.
We show that the asymptotic charges associated with Lorentz symmetries on past and future null infinity match in the limit to spatial infinity in a class of asymptotically-flat spacetimes. These are spacetimes that obey the Ashtekar-Hansen definition of asymptotic flatness at null and spatial infinity and satisfy an additional set of conditions which we lay out explicitly. Combined with earlier results on the matching of supertranslation charges, this shows that all Bondi-Metzner-Sachs (BMS) charges on past and future null infinity match in the limit to spatial infinity in this class of spacet…
Population studies of stellar-mass black-hole binaries have become major players in gravitational-wave astronomy. The underlying assumptions are that the targeted source parameters refer to the same quantities for all events in the catalog and are included when modeling selection effects. Both these points have so far been neglected when estimating the orientations of the black-hole spins. In particular, the detector-frame gravitational-wave frequency used to define frequency-dependent quantities (e.g., 20 Hz) introduces an inconsistent reference between events at the population level. We solv…
Matching conditions at null infinity in the presence of logarithms: the role of advanced and retarded radiation
Facultad de Ingeniería, Universidad San Sebastián（圣塞巴斯蒂安大学工程学院）；Université Libre de Bruxelles（布鲁塞尔自由大学）；International Solvay Institutes（国际索尔维研究所）；Collège de France, Université PSL（法兰西公学院，巴黎文理研究大学）；Centro de Estudios Científicos (CECs)（科学研究中心）；Erwin Schrödinger Int. Institute for Mathematics and Physics, University of Vienna（维也纳大学埃尔温·薛定谔数学与物理国际研究所）
Zero rest-mass fields of spin 1 (the electromagnetic field) and spin 2 propagating on flat space and their corresponding Newman-Penrose (NP) constants are studied near spatial infinity. The aim of this analysis is to clarify the correspondence between data for these fields on a spacelike hypersurface and the value of their corresponding NP constants at future and past null infinity. To do so, Friedrich's framework of the cylinder at spatial infinity is employed to show that, expanding the initial data in terms spherical harmonics and powers of the geodesic spatial distance $ρ$ to spatial infin…
We resume former discussions of the conformally invariant wave equation on a Schwarzschild background, with a particular focus on the behaviour of solutions near the 'cylinder', i.e. Friedrich's representation of spacelike infinity. This analysis can be considered a toy model for the behaviour of the full Einstein equations and the resulting logarithmic singularities that appear to be characteristic for massive spacetimes. The investigation of the Cauchy problem for the conformally invariant wave equation (Frauendiener and Hennig 2018, Class. Quantum Grav. 35, 065015) showed that solutions gen…
Linear zero-rest-mass fields generically develop logarithmic singularities at the critical sets where spatial infinity meets null infinity. Friedrich's representation of spatial infinity is ideally suited to study this phenomenon. These logarithmic singularities are an obstruction to the smoothness of the zero-rest-mass field at null infinity and, in particular, to peeling. In the case of the spin-2 field it has been shown that these logarithmic singularities can be precluded if the initial data for the field satisfies a certain regularity condition involving the vanishing, at spatial infinity…
Characterization of (asymptotically) Kerr-de Sitter-like spacetimes at null infinity
本文研究了具有正宇宙学常数$Λ$的爱因斯坦真空场方程的解$(\mathcal{M}, g)$，该方程允许一个光滑的零无穷$\mathcal{J}^-$ à la Penrose和一个Killing矢量场，其相关的Mars-Simon张量（MST）为零.这项工作的主要目的是提供一个表征这些时空的柯西数据$\mathcal{J}^-$。在此过程中，我们还研究了MST不消失的时空。在这种情况下，其定义中存在由标量函数$Q$捕获的模糊性。我们分析了不同选择的$Q$的MST的属性。在这样做的时候，我们导致的“渐近克尔-德西特类时空”的定义，我们也在$\mathcal{J}^-$的渐近数据方面的特点。
We study the quantum analogue of the classical process of superradiance for a massless charged scalar field on a static charged black hole space-time. We show that an "in" vacuum state, which is devoid of particles at past null infinity, contains an outgoing flux of particles at future null infinity. This radiation is emitted in the superradiant modes only, and is nonthermal in nature.
A scattering theory for the wave equation on Kerr black hole exteriors
在一般次极值情形|a| <M下，我们发展了Kerr外背景上标量波动方程的确定性物理空间散射理论.特别是，我们证明了相应的结果“散射状态的存在性和唯一性”和“渐近完备性”，我们还表明，由此产生的“散射矩阵”映射辐射场在过去的地平线和过去的零无穷远辐射场在未来的地平线和未来的零无穷远是一个有界算子。后者使我们能够给出超辐射反射的时域理论。散射矩阵的有界性特别表明，与进入的有限能量波包在过去的零无穷大的解的最大放大是有界的。在频率方面，这对应于新的说法，即适当归一化的反射和透射系数独立于频率参数均匀地有界。我们进一步补充这一点，证明超辐射反射确实放大了能量辐射到未来零无限的合适的波包如上所述。结果利用了我们最近证明[M.达费莫斯岛Rodnianski和Y. Shlapentokh-Rothman，Decay for the solutions of the wave equation on Kerr external spacetimes III：the full subextremal case |a| <M，arXiv：1402.6034] of the solutions of the boundness and decay for the solutions of the Cauchy problem so to apply in the class of solutions w…
We show that the causal properties of asymptotically flat spacetimes depend on their dimensionality: while the time-like future of any point in the past conformal infinity $\mathcal{I}^-$ contains the whole of the future conformal infinity $\mathcal{I}^+$ in $(2+1)$ and $(3+1)$ dimensional Schwarzschild spacetimes, this property (which we call the Penrose property) does not hold for $(d+1)$ dimensional Schwarzschild if $d>3$. We also show that the Penrose property holds for the Kerr solution in $(3+1)$ dimensions, and discuss the connection with scattering theory in the presence of positive ma…
