Kinematically forbidden processes may be allowed in the presence of external gravitational fields. These ca be taken into account by introducing generalized particle momenta. The corresponding transition probabilities can then be calculated to all orders in the metric deviation from the field-free expressions by simply replacing the particle momenta with their generalized counterparts. The procedure applies to particles of any spin and to any gravitational fields. transition probabilities, emission power, and spectra are, to leading order, linear in the metric deviation. It is also shown how a small dissipation term in the particle wave equations can trigger a strong backreaction that introduces resonances in the radiative process and deeply affects the resulting gravitational background.
We extend our recent analysis (Ferrando J J and Sáez J A 2012 Class. Quantum Grav. 29 075012) on the Bel radiative gravitational fields to the super-energy radiative gravitational fields defined by Garc\'ıa-Parrado (Class. Quantum Grav. 25 015006). We give an intrinsic characterization of the {\it new radiative fields}, and consider some distinguished classes of both radiative and non radiative fields. Several super-energy inequalities are improved.
We analyze the concept of intrinsic radiative gravitational fields defined by Bel and we show that the three radiative types, N, III and II, correspond with the three following different physical situations: {\it pure radiation}, {\it asymptotic pure radiation} and {\it generic} (non pure, non asymptotic pure) {\it radiation}. We introduce the concept of {\em observer at rest} with respect to the gravitational field and that of {\em proper super-energy} of the gravitational field and we show that, for non radiative fields, the minimum value of the relative super-energy density is the proper su…
Radiative losses have traditionally been neglected in the calculation of thermal noise of transmissive optical elements because for the most commonly used geometries they are small compared to losses due to thermal conduction. We explore the use of such transmissive optical elements in extremely noise-sensitive environments such as the arm cavities of future gravitational-wave interferometers. This drives us to a geometry regime where radiative losses are no longer negligible. In this paper we derive the thermo-refractive noise associated with such radiative losses and compare it to other know…
A formalism is introduced which may describe both standard linearized waves and gravitational waves in Isaacson's high-frequency limit. After emphasizing main differences between the two approximation techniques we generalize the Isaacson method to non-vacuum spacetimes. Then we present three large explicit classes of solutions for high-frequency gravitational waves in particular backgrounds. These involve non-expanding (plane, spherical or hyperboloidal), cylindrical, and expanding (spherical) waves propagating in various universes which may contain a cosmological constant and electromagnetic…
We derive the matching conditions between FLRW and generalised Vaidya spacetimes with spherical, planar or hyperbolic symmetry, across timelike hypersurfaces. We then construct new models of gravitational collapse of FLRW spacetimes with a negative cosmological constant having electromagnetic radiation in the exterior. The final state of the collapse are asymptotically AdS black holes with spherical, toroidal or higher genus topologies. We analyse the collapse dynamics including trapped surface formation, for various examples.
Extremely high precision of near-future radio/optical interferometric observatories like SKA, Gaia, SIM and the unparalleled sensitivity of LIGO/LISA gravitational-wave detectors demands more deep theoretical treatment of relativistic effects in the propagation of electromagnetic signals through variable gravitational fields of the solar system, oscillating and precessing neutron stars, coalescing binary systems, exploding supernova, and colliding galaxies. Especially important for future gravitational-wave observatories is the problem of propagation of light rays in the field of multipolar gr…
We revisit the issue of memory effects, i.e. effects giving rise to a net cumulative change of the configuration of test particles, using a toy model describing the emission of radiation by a compact source and focusing on the scalar, hence non-radiative, part of the Riemann curvature. Motivated by the well known fact that gravitational radiation is accompanied by a memory effect, i.e. a permanent displacement of the relative separation of test particles, present after radiation has passed, we investigate the existence of an analog effect in the non-radiative part of the gravitational field. W…
Working within the post-Minkowskian approach to General Relativity, we prove that the radiation-reaction to the emission of gravitational waves during the large-impact-parameter scattering of two (classical) point masses modifies the conservative scattering angle by an additional contribution of order $G^3$ which involves a high-energy (or massless) logarithmic divergence of opposite sign to the one contained in the third-post-Minkowskian result of Bern et al. [Phys. Rev. Lett. {\bf 122}, 201603 (2019)]. The high-energy limit of the resulting radiation-reaction-corrected (classical) scattering…
We present a class of conformally flat solutions of the Einstein's field equations for spherical systems undergoing gravitational collapse accompanied with radial heat flux. The interior space-time of the collapsing matter is chosen to be conformal to the Robertson-Walker space-time so that its Weyl tensor vanishes identically. The conditions which ensure smooth matching of the interior space-time of the collapsing system, across its boundary, with the exterior space-time of a radiating star which is described by Vaidya metric lead to an equation governing its overall subsequent evolution. New…
In this paper we consider some aspects of the relativistic dynamics of a cylindrical shell of counter rotating particles. In some sense these are the simplest systems with a physically acceptable matter content that display in a well defined sense an interaction with the radiative modes of the gravitational field. These systems have been analyzed previously, but in most cases resorting to approximations, or considering a particular form for the initial value data. Here we show that there exists a family of solutions where the space time inside the shell is flat and the equation of motion of th…
We demonstrate how plane fronted waves with colliding wave fronts are the asymptotic limit of spherical electromagnetic and gravitational waves. In the case of the electromagnetic waves we utilize Bateman's representation of radiative solutions of Maxwell's vacuum field equations. The gravitational case involves a novel form of the radiative Robinson--Trautman solutions of Einstein's vacuum field equations.
The evolution of spheroids of matter emitting gravitational waves and null radiation field is studied in the realm of radiative Robinson-Trautman spacetimes. The null radiation field is expected in realistic gravitational collapse, and can be either an incoherent superposition of waves of electromagnetic, neutrino or massless scalar fields. We have constructed the initial data identified as representing the exterior spacetime of uniform and non-uniform spheroids of matter. By imposing that the radiation field is a decreasing function of the retarded time, the Schwarzschild solution is the asym…
Single-vertex Feynman diagrams represent the dominant contribution to physical processes, but are frequently forbidden kinematically. This is changed when the particles involved propagate in a gravitational background and acquire an effective mass. Procedures are introduced that allow the calculation of lowest order diagrams, their corresponding transition probabilities, emission powers and spectra to all orders in the metric deviation, for particles of any spin propagating in gravitational fields described by any metric. Physical properties of the "space-time medium" are also discussed. It is…
The extremely high precision of current astronomical observations demands a much better theoretical treatment of relativistic effects in the propagation of electromagnetic signals through variable gravitational fields of isolated astronomical systems emitting gravitational waves. This paper presents a consistent approach giving a complete and exhaustive solution of this problem in the first post-Minkowskian approximation of general relativity.
We give a new definition, based on considerations of well-posedness for a certain asymptotic initial value problem, of the phase space for the radiative degrees of freedom of the gravitational field in exact General Relativity. This space fibres over the space of final states, with the fibres being the purely radiative degrees of freedom. The symplectic form is rigorously identified. The infrared sectors are shown to be the level surfaces of a moment map of an action of the quotient group Supertranslations/Translations. A similar result holds for Electromagnetism in Minkowski space.
It is shown that the motion of a multielectron atom in an external gravitational field in a good approximation is described by system of the Mathisson-Papapetrou equations, if we put as a classical angular momentum of the atom the expectation value of the operator of the full angular momentum of the system, which includes spins of the nucleus and electrons, and orbital momentums of the electrons in the atom.
We model the behaviour of a relativistic spherically symmetric shearing fluid undergoing gravitational collapse with heat flux. It is demonstrated that the governing equation for the gravitational behaviour is a Riccati equation. We show that the Riccati equation admits two classes of new solutions in closed form. We regain particular models, obtained in previous investigations, as special cases. A significant feature of our solutions is the general spatial dependence in the metric functions which allows for a wider study of the physical features of the model, such as the behaviour of the caus…
The first order perturbations of the energy levels of a stationary hydrogen atom in static external gravitational field, with Schwarzschild metric, are investigated. The energy shifts are calculated for the relativistic 1S, 2S, 2P, 3S, 3P, 3D, 4S, 4P, 4D and 4F levels. The results show that the energy-level shifts of the states with total angular momentum quantum number 1/2 are all zero, and the ratio of absolute energy shifts with total angular momentum quantum number 5/2 is 1:4:5. This feature can be used to help us to distinguish the gravitational effect from other effect.
Neutrino asymmetry in general relativistic radiative spacetime exterior to spinning stars is investigating by making use of Newmann-Penrose (NP) spin coefficient formalism. It is shown that neutrino current depends on the direction of rotation of the star. The solution is obtained in test field approximation where the neutrinos do not generate gravitational fields.
The paper gives an introduction to the gravitational radiation theory of isolated sources and to the propagation properties of light rays in radiative gravitational fields. It presents a theoretical study of the generation, propagation, back-reaction, and detection of gravitational waves from astrophysical sources. After reviewing the various quadrupole-moment laws for gravitational radiation in the Newtonian approximation, we show how to incorporate post-Newtonian corrections into the source multipole moments, the radiative multipole moments at infinity, and the back-reaction potentials. We f…
We derive the radiation characteristics of an accelerated, charged particle in a model due to Caianiello in which the proper acceleration of a particle of mass $m$ has the upper limit $\mathcal{A}_m=2mc^3/\hbar$. We find two power laws, one applicable to lower accelerations, the other more suitable for accelerations closer to $\mathcal{A}_m$ and to the related physical singularity in the Ricci scalar. Geometrical constraints and power spectra are also discussed. By comparing the power laws due to the maximal acceleration with that for particles in gravitational fields, we find that the model o…
The influence of radiative corrections on the photon propagation in a gravitational background is investigated without the low-frequency approximation $ω\ll m$. The conclusion is made in this way that the velocity of light can exceed unity.
We compute to high post-Newtonian accuracy the 4-momentum (linear momentum, and energy), radiated as gravitational waves in a two-body system undergoing gravitational scattering. We include, for the first time, all the relevant {\it time-asymmetric} effects that arise when consistently going three post Newtonian orders beyond the leading post Newtonian order. We find that the inclusion of time-asymmetric radiative effects (both in tails and in the radiation-reacted hyperbolic motion) is crucial to ensure the mass-polynomiality of the post-Minkowskian expansion ($G$ expansion) of the radiated 4…
The cosmic strings(CSs) may be one important source of gravitational waves(GWs), and it has been intensively studied due to its special properties such as the cylindrical symmetry. The CSs would generate not only usual continuous GW, but also impulsive GW that brings more concentrated energy and consists of different GW components broadly covering low-, intermediate- and high-frequency bands simultaneously. These features might underlie interesting electromagnetic(EM) response to these GWs generated by the CSs. In this paper, with novel results and effects, we firstly calculate the analytical …
An astrophysically realistic model of wave dynamics in black-hole spacetimes must involve a non-spherical background geometry with angular momentum. We consider the evolution of gravitational (and electromagnetic) perturbations in rotating Kerr spacetimes. We show that a rotating Kerr black hole becomes `bald' slower than the corresponding spherically-symmetric Schwarzschild black hole. Moreover, our results turn over the traditional belief (which has been widely accepted during the last three decades) that the late-time tail of gravitational collapse is universal. In particular, we show that …
In the study of covariant wave equations, linear gravity manifests itself through the metric deviation $γ_{μν}$ and a two-point vector potential $K_λ$ itself constructed from $γ_{μν}$ and its derivatives. The simultaneous presence of the two gravitational potentials is non contradictory. Particles also assume the character of quasiparticles and $K_λ$ carries information about the matter with which it interacts. We consider the influence of $K_λ$ on the dispersion relations of the particles involved, the particles' motion, quantum tunneling through a horizon, radiation, energy-momentum dissipat…
We give a conceptual exposition of aspects of gravitational radiation, especially in relation to energy. Our motive for doing so is that the strong analogies with electromagnetic radiation seem not to be widely enough appreciated. In particular, we reply to some recent papers in the philosophy of physics literature that seem to deny that gravitational waves carry energy. Our argument is based on two points: (i) that for both electromagnetism and gravity, in the presence of material sources, radiation is an effective concept, unambiguously emerging only in certain regimes or solutions of the th…
A numerical-relativity calculation yields in general a solution of the Einstein equations including also a radiative part, which is in practice computed in a region of finite extent. Since gravitational radiation is properly defined only at null infinity and in an appropriate coordinate system, the accurate estimation of the emitted gravitational waves represents an old and non-trivial problem in numerical relativity. A number of methods have been developed over the years to "extract" the radiative part of the solution from a numerical simulation and these include: quadrupole formulas, gauge-i…
We consider a monopole detector interacting with a massive scalar field. The radiative processes are discussed from the accelerated frame point of view. After this, we obtain the Minkowski vacuum stress tensor measured by the accelerated observer using a non-gravitational stress tensor detector as discussed by Ford and Roman (PRD 48, 776 (1993)). Finally, we analyse radiative processes of the monopole detector travelling in a world line that is inertial in the infinite past and has a constant proper acceleration in the infinite future.
The gravitational radiation backreaction effects are considered in the Lense-Thirring approximation. New methods for parameterizing the orbit and for averaging the instantaneous radiative losses are developed. To first order in the spin S of the black hole, both in the absence and in the presence of gravitational radiation, a complete description of the test-particle orbit is given. This is achieved by two improvements over the existing descriptions. First, by introducing new angle variables with a straightforward geometrical meaning. Second, by finding a new parametrization of a generic orbit…
We explore, in the framework of linearized quantum gravity, the induced gravitational interaction between two gravitationally polarizable objects in their ground states in the presence of an external quantized gravitational radiation field. The interaction energy decreases as $r^{-5}$ in the near regime, and oscillates with a decreasing amplitude proportional to $r^{-1}$ in the far regime, where $r$ is the distance between the two objects. The interaction can be either attractive or repulsive depending on the propagation direction, polarization and frequency of the external gravitational field…
The conventional gravitational memory effect is a relative displacement in the position of two detectors induced by radiative energy flux. We find a new type of gravitational `spin memory' in which beams on clockwise and counterclockwise orbits acquire a relative delay induced by radiative angular momentum flux. It has recently been shown that the displacement memory formula is a Fourier transform in time of Weinberg's soft graviton theorem. Here we see that the spin memory formula is a Fourier transform in time of the recently-discovered subleading soft graviton theorem.
We study realistic models of relativistic radiating stars undergoing gravitational collapse which have vanishing Weyl tensor components. Previous investigations are generalised by retaining the inherent nonlinearity at the boundary. We transform the boundary condition to an Abel equation of the first kind. A variety of nonlinear solutions are generated all of which can be written explicitly. Several classes of infinite solutions exist.
The Chern-Simons-like gravitational action is evaluated explicitly in four dimensional space-time by radiative corrections at one-loop level. The calculation is performed in fermionic sector where the Dirac fermions interact with the background gravitational field, including the parity-violating term \barψ\bsγ_5ψ. The investigation takes into account the weak field approximation and dimensional regularization scheme.
We study the quantum particle creation in a toy model of spherically symmetric gravitational collapse whose final product is not a black hole but a gravastar. Precedent studies revealed that even in the case of the gravitational collapse to form a horizonless ultra-compact object, thermal radiation named transient Hawking radiation is generated at the late stage of the gravitational collapse, and a sudden stop of collapsing motion to form a horizonless ultra-compact object causes one or two bursts of quantum particle creation. The very different behavior of the model studied in this paper from…
The estimation of radiative modes is a central problem in gravitational wave theory, with essential applications in signal modeling and data analysis. This problem is complicated by most astrophysically relevant systems' not having modes that are analytically tractable. A ubiquitous workaround is to use not modes, but multipole moments defined by spin weighted spherical harmonics. However, spherical multipole moments are only related to the modes of systems without angular momentum. As a result, they can obscure the underlying physics of astrophysically relevant systems, such as binary black h…
We investigate, in the framework of linearized quantum gravity, the induced quantum gravitational interaction between two ground-state objects with permanent quadrupole moments, which are subjected to an external gravitational radiation field. Compared with the nonpolar case, there exists an additional term in the leading-order field-induced interobject interaction between two polar objects. This term arises when a real graviton is scattered by the same object center with coupling between the two objects occurring via the exchange of a single virtual graviton, and the interaction is thus relev…
We study the fate of a collapsing star on the brane in a generalized braneworld gravity with bulk matter. Specifically, we investigate for the possibility of having a static exterior for a collapsing star in the radiative bulk scenario. Here, the nonlocal correction due to bulk matter is manifest in an induced mass that adds up to the physical mass of the star resulting in an effective mass. A Schwarzschild solution for the exterior in terms of this effective mass is obtained, which reveals that even if the star exchanges energy with the bulk, the exterior may appear to be static to a branewor…
We study the radiation reaction on cosmic strings due to the emission of dilatonic, gravitational and axionic waves. After verifying the (on average) conservative nature of the time-symmetric self-interactions, we concentrate on the finite radiation damping force associated with the half-retarded minus half-advanced ``reactive'' fields. We revisit a recent proposal of using a ``local back reaction approximation'' for the reactive fields. Using dimensional continuation as convenient technical tool, we find, contrary to previous claims, that this proposal leads to antidamping in the case of the …
The linear-order effects of radiation-reaction on the classical scattering of two point masses, in General Relativity, are derived by a variation-of-constants method. Explicit expressions for the radiation-reaction contributions to the changes of 4-momentum during scattering are given to linear order in the radiative losses of energy, linear-momentum and angular momentum. The polynomial dependence on the masses of the 4-momentum changes is shown to lead to non-trivial identities relating the various radiative losses. At order $G^3$ our results lead to a streamlined classical derivation of resu…
We obtain a family of exact solutions describing magnetized black holes in an external gravitational field. Locally the solutions can be interpreted as representing the near-horizon region of a black hole, which interacts with a surrounding matter distribution producing a strong magnetic field. Thus, the solutions reflect the influence of both a gravitational and an electromagnetic external potential in the strong field regime. The static members in the family are generalizations of the Schwarzschild solution in the described environment, while the rotating ones generalize the magnetized Reiss…
We compute classical gravitational observables for the scattering of two spinless black holes in general relativity and $\mathcal N {=} 8$ supergravity in the formalism of Kosower, Maybee, and O'Connell (KMOC). We focus on the gravitational impulse with radiation reaction and the radiated momentum in black hole scattering at $\mathcal O(G^3)$ to all orders in the velocity. These classical observables require the construction and evaluation of certain loop-level quantities which are greatly simplified by harnessing recent advances from scattering amplitudes and collider physics. In particular, …
In this paper we construct an effective field theory (EFT) that describes long wavelength gravitational radiation from compact systems. To leading order, this EFT consists of the multipole expansion, which we describe in terms of a diffeomorphism invariant point particle Lagrangian. The EFT also systematically captures "post-Minkowskian" corrections to the multipole expansion due to non-linear terms in general relativity. Specifically, we compute long distance corrections from the coupling of the (mass) monopole moment to the quadrupole moment, including up to two mass insertions. Along the wa…
We study the interaction of massless scalar fields with self-gravitating neutron stars by means of fully dynamic numerical simulations of the Einstein-Klein-Gordon perfect fluid system. Our investigation is restricted to spherical symmetry and the neutron stars are approximated by relativistic polytropes. Studying the nonlinear dynamics of isolated neutron stars is very effectively performed within the characteristic formulation of general relativity, in which the spacetime is foliated by a family of outgoing light cones. We are able to compactify the entire spacetime on a computational grid a…
In a region with a boundary, the gravitational phase space consists of radiative modes in the interior and edge modes at the boundary. Such edge modes are necessary to explain how the region couples to its environment. In this paper, we characterise the edge modes and radiative modes on a null surface for the tetradic Palatini--Holst action. Our starting point is the definition of the action and its boundary terms. We choose the least restrictive boundary conditions possible. The fixed boundary data consists of the radiative modes alone (two degrees of freedom per point). All other boundary fi…
In a vacuum spacetime equipped with the Bondi's radiating metric which is asymptotically flat at spatial infinity including gravitational radiation ({\bf Condition D}), we establish the relation between the ADM total energy-momentum and the Bondi energy-momentum for perturbed radiative spatial infinity. The perturbation is given by defining the "real" time the sum of the retarded time, the Euclidean distance and certain function $f$.
By using elementary astrophysical concepts, we show that for any self-luminous astrophysical object, the ratio of radiation energy density inside the body (rho_r) and the baryonic energy density (rho_0) may be crudely approximated, in the Newtonian limit, as rho_r/rho_0 ~ GM/Rc^2, where G is constant of gravitation, c is the speed of light, M is gravitational mass, and R is the radius of the body. The key idea is that radiation quanta must move out in a diffusive manner rather than free stream inside the body of the star. When one would move to the extreme General Realtivistic case i.e., if th…
