In the paper we study propagation of light in general relativity through a spacetime filled with cold plasma with infinite conductivity. We use the geometric optics based on Synge's approach. As the main result we provide a formula for calculation of spectral flux of radiation emitted from a pointlike source. The formula employs connecting vectors that are obtained by integrating the ray deviation equation along the reference ray connecting the source and observation event. As a byproduct we formulate Etherington's reciprocity theorem with the inclusion of plasma, interrelating angular size distance and luminosity distance. We also discuss the Liouville theorem and its formulation in terms of connecting vectors.
We study a binary system composed of point particles of unequal masses in eccentric orbits in the linear regime of the characteristic formulation of general relativity, generalising a previous study found in the literature in which a system of equal masses in circular orbits is considered. We also show that the boundary conditions on the time-like world tubes generated by the orbits of the particles can be extended beyond circular orbits. Concerning the power lost by the emission of gravitational waves, it is directly obtained from the Bondi's News function. It is worth stressing that our resu…
Conceptual tensions between quantum mechanics and general relativity: Are there experimental consequences, e.g., superconducting transducers between electromagnetic and gravitational radiation?
The weight of light: colliding pulses of radiation in General Relativity
CENTRA, Departamento de Física, Instituto Superior Técnico – IST, Universidade de Lisboa – UL（里斯本大学高等理工学院物理系CENTRA）；Center of Gravity, Niels Bohr Institute（尼尔斯·玻尔研究所引力中心）
Gravitational effect of "magnetic type" -- those having a curl-like character over large spheres -- are investigated, for isolated systems. The Bondi-Sachs-Newman-Penrose formalism clarifies a number of points, especially related to radiation memory. It is shown that the "memory tensor" is equivalent to the change in Bondi shear, from before to after the emission of radiation. This means that if magnetic radiation memory is present, at least one of the intervals bracketing the radiation must have non-zero magnetic shear but vanishing radiation. Such intervals, called here CPMS regimes, are sho…
(Short abstract). In Galilean physics, the universality of free fall implies an inertial frame, which in turns implies that the mass m of the falling body is omitted. Otherwise, an additional acceleration proportional to m/M would rise either for an observer at the centre of mass of the system, or for an observer at a fixed distance from the centre of mass of M. These elementary, but overlooked, considerations fully respect the equivalence principle and the identity of an inertial or a gravitational pull for an observer in the Einstein cabin. They value as fore-runners of the self-force and ga…
The center of mass and spin for isolated sources of gravitational radiation that move at relativistic speeds are defined. As a first step, we also present these definitions in flat space. This contradicts some general wisdom given in textbooks claiming that such definitions are not covariant and thus, have no physical meaning. We then generalize the definitions to asymptotically flat spacetimes giving their equations of motion when gravitational radiation is emitted by the isolated sources. The resulting construction has some similarities with the Mathisson-Papapetrou equations which describes…
General relativity explains gravitational radiation from binary black hole or neutron star mergers, from core-collapse supernovae and even from the inflation period in cosmology. These waves exhibit a unique effect called memory or Christodoulou effect, which in a detector like LIGO or LISA shows as a permanent displacement of test masses and in radio telescopes like NANOGrav as a change in the frequency of pulsars' pulses. It was shown that electromagnetic fields and neutrino radiation enlarge the memory. Recently it has been understood that the two types of memory addressed in the literature…
General relativity (GR) has been extensively tested in the solar system and in binary pulsars, but never in the strong-field, dynamical regime. Soon, gravitational-wave (GW) detectors like Advanced LIGO and eLISA will be able to probe this regime by measuring GWs from inspiraling and merging compact binaries. One particularly interesting alternative to GR is scalar-tensor gravity. We present progress in the calculation of second post-Newtonian (2PN) gravitational waveforms for inspiraling compact binaries in a general class of scalar-tensor theories. The waveforms are constructed using a stand…
We implement advanced Riemann solvers HLLC and HLLD \cite{Mignone:2005ft,MUB:2009} together with an advanced constrained transport scheme \cite{Gardiner:2007nc} in a numerical-relativity neutrino-radiation magnetohydrodynamics code. We validate our implementation by performing a series of one- and multi-dimensional test problems for relativistic hydrodynamics and magnetohydrodynamics in both Minkowski spacetime and a static black hole spacetime. We find that the numerical solutions with the advanced Riemann solvers are more accurate than those with the HLLE solver \cite{DelZanna:2002rv}, which…
The topic of this thesis is the so-called Non-Relativistic General Relativity, an effective field theory approach proposed by Goldberger and Rothstein to study the conservative and dissipative dynamics of binary systems of compact objects in the post-Newtonian expansion. In the first part of the thesis we review this approach in the simplest possible case: a binary of non-spinning black holes at leading post-Newtonian order, both for the conservative and dissipative sector in general relativity. In the second part of the thesis we present the so-called Kaluza-Klein parametrization of the metri…
[Abridged] This review surveys the theory of gravitational self-force in curved spacetime and its application to the gravitational two-body problem in the extreme-mass-ratio regime. We first lay the relevant formal foundation, describing the rigorous derivation of the equation of self-forced motion using matched asymptotic expansions and other ideas. We then review the progress that has been achieved in numerically calculating the self-force and its physical effects in the astrophysical scenario of a compact object inspiralling into a (rotating) massive black hole. We highlight the way in whic…
We endeavour to illustrate the physical relevance of the Landauer principle applying it to different important issues concerning the theory of gravitation. We shall first analyze, in the context of general relativity, the consequences derived from the fact, implied by Landauer principle, that information has mass. Next, we shall analyze the role played by the Landauer principle in order to understand why different congruences of observers provide very different physical descriptions of the same space--time. Finally, we shall apply the Landauer principle to the problem of gravitational radiatio…
Gravitational waves deliver information in exquisite detail about astrophysical phenomena, among them the collision of two black holes, a system completely invisible to the eyes of electromagnetic telescopes. Models that predict gravitational wave signals from likely sources are crucial for the success of this endeavor. Modeling binary black hole sources of gravitational radiation requires solving the Eintein equations of General Relativity using powerful computer hardware and sophisticated numerical algorithms. This proceeding presents where we are in understanding ground-based gravitational …
Null Asymptotics of Solutions of the Einstein-Maxwell Equations in General Relativity and Gravitational Radiation
我们证明了在时空中求解Einstein-Maxwell（EM）方程时，电磁场对引力波的非线性记忆效应的贡献是最高阶的。在[5] D. Christodoulou证明了引力波具有非线性记忆。他讨论了如何在激光干涉仪引力波探测器中将这种效应测量为测试质量的永久位移。赫里斯托杜卢在爱因斯坦真空（EV）的情况下推导出了这种永久位移的精确公式。我们在定理6中证明，对于EM方程，该永久位移表现出来自电磁场的项。这一项与支配EV情形的纯引力项处于相同的最高阶。另一方面，在第三章中，我们证明了对于首阶，电磁场的存在并不改变测试质量的瞬时位移。根据D. Christodoulou在[5]中给出的渐近性和N. Zipser在文[8]和[9]中，通过求解电磁方程，研究了时空中零无穷远处的引力辐射。本文研究了文献[9]中导出的零无穷远处的Bondi质量损失公式。我们证明了[9]中的质量损失公式与[4]中得到的Bondi坐标下的质量损失公式是相容的。我们观察到，电磁场的存在使辐射的总能量增加到无穷大，直到首阶。此外，我们在定理7中计算了零无穷远处面积半径的极限。
We perform neutrino radiation-hydrodynamics simulations for the merger of asymmetric binary neutron stars in numerical relativity. Neutron stars are modeled by soft and moderately stiff finite-temperature equations of state (EOS). We find that the properties of the dynamical ejecta such as the total mass, neutron richness profile, and specific entropy profile depend on the mass ratio of the binary systems for a given EOS in a unique manner. For the soft EOS (SFHo), the total ejecta mass depends weakly on the mass ratio, but the average of electron number per baryon ($Y_e$) and specific entropy…
