The extreme Reissner–Nordström (ERN) solution has a discrete conformal isometry that maps the future event horizon to future null infinity and vice versa, the Couch–Torrence (CT) inversion isometry. We study the dynamics of a probe Maxwell field on the ERN solution in light of this symmetry. We present a gauge fixing that is compatible with the inversion symmetry. The gauge fixing allows us to relate

We investigate stress–energy tensors constructed from the delta function on a worldline. We concentrate on quadrupoles as they make an excellent model for the dominant source of gravitational waves and have significant novel features. Unlike the dipole, we show that the quadrupole has 20 free components which are not determined by the properties of the stress–energy tensor. These need to be derived

BepiColombo ESA/JAXA mission is currently in its 7 year cruise phase towards Mercury. The Mercury orbiter radioscience experiment (MORE), one of the 16 experiments of the mission, will start its scientific investigation during the superior solar conjunction (SSC) in March 2021 with a test of general relativity (GR). Other solar conjunctions will follow during the cruise phase, providing several opportunities

We consider the question of whether solutions of Klein–Gordon equations on asymptotically anti-de Sitter spacetimes can be uniquely continued from the conformal boundary. Positive answers were first given in [15, 16], under suitable assumptions on the boundary geometry and with boundary data imposed over a sufficiently long timespan. The key step was to establish Carleman estimates for Klein–Gordon

The Lewis solutions describe the exterior gravitational field produced by infinitely long rotating cylinders, and are useful models for global gravitational effects. When the metric parameters are real (Weyl class), the exterior metrics of rotating and static cylinders are locally indistinguishable, but known to globally differ. The significance of this difference, both in terms of physical effects

We consider vacuum spacetimes with a crushing singularity. Under some scale-invariant curvature bounds, we relate the existence of Kasner-like regions to the asymptotics of spatial volume densities.

We construct a class of conserved currents for linearized gravity on a Kerr background. Our procedure, motivated by the current for scalar fields discovered by Carter (1977), is given by taking the symplectic product of solutions to the linearized Einstein equations that are defined by symmetry operators. We consider symmetry operators that are associated with separation of variables in the Teukolsky

The Kerr spacetime is perhaps the most astrophysically important of the currently known exact solutions to the Einstein field equations. Whenever spacetimes can be put in unit-lapse form it becomes possible to identify some very straightforward timelike geodesics, (the ‘rain’ geodesics), making the physical interpretation of these spacetimes particularly clean and elegant. The most well-known of these

In loop quantum gravity (LQG) the quantisation of general relativity leads to precise predictions for the eigenvalues of geometrical observables like volume and area, up to the value of the only free parameter of the theory, the Barbero–Immirzi (BI) parameter. With the help of the eigenvalues equation for the area operator, LQG successfully derives the Bekenstein–Hawking entropy of large black holes

We study asymptotically AdS generalizations of Melvin spacetimes, describing gravitationally bound tubes of magnetic flux. We find that narrow fluxtubes, carrying strong magnetic fields but little total flux, are approximately unchanged from the Λ = 0 case at scales smaller than the AdS scale. However, fluxtubes with weak fields, which for Λ = 0 can grow arbitrarily large in radius and carry unbounded

Galactic cosmic rays and solar energetic particles charge gold-platinum, free-falling test masses (TMs) on board interferometers for the detection of gravitational waves in space. The charging process induces spurious forces on the test masses that affect the sensitivity of these instruments mainly below 10 −3 Hz. Geant4 and FLUKA Monte Carlo simulations were carried out to study the TM charging process

This paper describes the electrodynamics of a null and force-free field in completely geometric terms. As was previously established in Menon (2020 Class. Quantum Grav. 37 245006), solutions to force-free electrodynamics are governed by the existence of certain special types of foliations of spacetime. Here the nature of the foliations in a coordinate-free formalism in the null case is prescribed.

We extend previous work (2020 Class. Quantum Grav. 37 075001) to the case of Maxwell’s equations with a source. Our work shows how to construct a vector potential for the Maxwell field on the Kerr–Newman background in a radiation gauge. The vector potential has a ‘reconstructed’ term obtained from a Hertz potential solving Teukolsky’s equation with a source, and a ‘correction’ term which is obtainable

In this paper, we consider dynamical Chern–Simons gravity with the identification of the scalar field coupled though the Pontryagin density with the axion dark matter, and we discuss the effects of the parametric resonance on gravitational waves (GWs). When we consider GWs in a coherently oscillating axion cloud, we confirm that significant resonant amplification of GWs occurs in a narrow frequency

We study stable circular orbits in spherically symmetric AdS black holes in various dimensions and their limiting innermost stable circular orbits. We provide analytic expressions for their size, angular velocity and angular momentum in a large black hole mass regime. The dual interpretation is in terms of meta-stable states not thermalising in typical thermal scales and whose existence is due to non-perturbative

The acceleration of the Universe is described as a consequence of the extrinsic curvature of a four dimensional space–time embedded in a five dimensional bulk space, defined by the Einstein–Hilbert principle. Using the linear approximation of the Nash–Greene embedding theorem, we obtain the related perturbed equations in which only the gravitational-tensor field equations contribute to the propagation

Eigenfunctions are shown to constitute privileged coordinates of self-dual Einstein spaces with the underlying governing equation being revealed as the general heavenly equation. The formalism developed here may be used to link algorithmically a variety of known heavenly equations. In particular, the classical connection between Plebański’s first and second heavenly equations is retrieved and interpreted

I point out a simple expression for the ‘Hubble’ parameter ##IMG## [http://ej.iop.org/images/0264-9381/38/4/045006/cqgabd146ieqn4.gif] {$\mathcal{H}$} , defined by Borde, Guth and Vilenkin in their proof of past incompleteness of inflationary spacetimes. I show that the parameter ##IMG## [http://ej.iop.org/images/0264-9381/38/4/045006/cqgabd146ieqn5.gif] {$\mathcal{H}$} which an observer O with four-velocity

Oscillons are dense nonperturbative objects that may be copiously produced in the preheating period after inflation. Oscillon preheatings are usually simulated with nonlinear matter interactions but in a rigid FLRW background, without taking into account the gravitational backreactions. We investigate the oscillon preheating scenario in full general relativity with a full numerical relativity scheme

This article deals with the study of the dynamics of particles in different wormhole geometries. Using the Jacobi metric approach we study the geodesic motion on the Morris–Thorne wormhole. We found the only stable circular orbit located at the throat. We show that the Gaussian curvature of the Jacobi metric is directly related with the wormhole flare-out condition. We provide a simple test for determining

We discuss the propagation of light in the C -metric. We discover that null geodesics admit circular orbits only for a certain family of orbital cones. Explicit analytic formulae are derived for the orbital radius and the corresponding opening angle fixing the cone. Furthermore, we prove that these orbits based on a saddle point in the effective potential are Jacobi unstable. This completes the stability

As part of the upgrade program of the advanced Virgo interferometer, the installation of new instrumented baffles surrounding the main test masses is foreseen. As a demonstrator, and to validate the technology, the existing baffle in the area of the input mode cleaner end-mirror will be first replaced by a baffle equipped with photodiodes. This paper presents detailed simulations of the light distribution

The possible existence of stable black holes with entropies larger than the corresponding Schwarzschild black hole has been discussed extensively. The recently proposed ‘rough’ black holes provide a concrete example of this. The fear is that, in accordance with the second law of thermodynamics, the familiar smooth-skinned black holes might spontaneously ‘wrinklify’ into such an object. We show that

We study the geometry of a general class of vacuum asymptotically anti-de Sitter spacetimes near the conformal boundary. In particular, the spacetime is only assumed to have finite regularity, and it is allowed to have arbitrary boundary topology and geometry. For the main results, we derive limits at the conformal boundary of various geometric quantities, and we use these limits to construct partial

After the recent GW170817 event of the two neutron stars merging, many string corrected cosmological theories confronted the non-viability peril. This was due to the fact that most of these theories produce massive gravitons primordially. Among these theories were the ones containing a non-minimal kinetic coupling correction term in the Lagrangian. In this work we demonstrate how these theories may

Accurate simulation of the propagation of light between the spacecraft of the laser interferometer space antenna (LISA) gravitational wave observatory will be a vital tool in determining the optical design of the telescopes used in the constellation. In this work, we examine the methods available for numerical simulation of this propagation, and consider the effect of an aberrated transmitting telescope

We investigate here the thermal properties of accretion disks in a spacetime for some galactic density profiles in spherical symmetry. The matter distributions have a finite outer radius with a naked central singularity. The luminosities of the accretion disks for some density profile models are found to be higher than those for a Schwarzschild black hole of the same mass. The slopes for the luminosity

We study scattering of short Gaussian pulses of axial gravitational waves by a spherically symmetric black hole that has swallowed one or more global monopoles. We qualitatively show how the response of the black hole to the impinging pulses depends both on the number of monopoles the black hole has swallowed and on the symmetry breaking scale of the model which gave rise to the monopoles. We use semianalytical

The Hamiltonian of intrinsic time gravity is elucidated. The theory describes Schrödinger evolution of our universe with respect to the fractional change of the total spatial volume. Gravitational interactions are introduced by extending Klauder’s momentric variable with similarity transformations, and explicit spatial diffeomorphism invariance is enforced via similarity transformation with exponentials

We derive a canonical form for skew-symmetric endomorphisms F in Lorentzian vector spaces of dimension three and four which covers all non-trivial cases at once. We analyze its invariance group, as well as the connection of this canonical form with duality rotations of two-forms. After reviewing the relation between these endomorphisms and the algebra of conformal Killing vectors of ##IMG## [http://ej

We obtain charged and rotating black hole solutions to the novel 3D Gauss–Bonnet theory of gravity recently proposed, both of which generalize the Banados–Teitelboim–Zanelli (BTZ) metric. The charged solutions are obtained in the Maxwell and Born–Infeld theories and feature ‘universal thermodynamics’—identical to the thermodynamics of their Einstein cousins. The rotating Gauss–Bonnet BTZ black holes

Recently it has been proposed that the Gauss–Bonnet coupling parameter of Lovelock gravity may suitably be rescaled in order to admit physically viable models of celestial phenomena such that higher curvature effects are active in standard four dimensions as opposed to the usual higher dimensions. We investigate the consequences of this modification in the context of stellar modelling. The evolution

We consider first order symmetry operators for the equations of motion of differential p -form fields in general D -dimensional background geometry of any signature for both massless and massive cases. For p = 1 and p = 2 we give the general forms of the symmetry operators. Then we find a class of symmetry operators for arbitrary p and D , which is naturally suggested by the lower p results.

We investigate stability issues for steady states of the spherically symmetric Einstein–Vlasov system numerically in Schwarzschild, maximal areal, and Eddington–Finkelstein coordinates. Across all coordinate systems we confirm the conjecture that the first binding energy maximum along a one-parameter family of steady states signals the onset of instability. Beyond this maximum perturbed solutions either

The null limits of the Lemaître–Tolman and Szekeres spacetimes are known to be the Vaidya and news-free Robinson–Trautman metrics. We generalise this result to the case of non-zero Λ, and then ask whether the reverse process is possible—is there a systematic procedure to retrieve the timelike-dust metric from the null-dust case? We present such an algorithm for re-constructing both the metric and matter

Causal concept for the general black hole shadow is investigated, instead of the photon sphere. We define several ‘wandering null geodesics’ as complete null geodesics accompanied by repetitive conjugate points, which would correspond to null geodesics on the photon sphere in Schwarzschild spacetime. We also define a ‘wandering set’, that is, a set of totally wandering null geodesics as a counterpart

This note addresses quasinormal mode (QNM) frequencies of four-dimensional asymptotically de Sitter rotating black holes. The main motivation is that Mathematica 12.1 has implemented a new family of special functions: Heun functions . Using the fact that Teukolsky’s equations for Kerr–de Sitter black holes are mapped to Heun’s equations, we are able to compute their QNM frequencies by the Heun function

The constraint algebra is derived in the second order tetrad Hamiltonian formalism of the bigravity. This is done by a straightforward calculation without involving any insights, implicit functions, and Dirac brackets. The tetrad approach is the only way to present the bigravity action as a linear functional of lapses and shifts and the Hassan–Rosen transform (characterized as ‘a complicated redefinition

We study the utility of chains defined on causal sets in estimating continuum properties like the curvature, the proper time and the spacetime dimension through a numerical analysis. In particular, we show that in d S 2 and FLRW 3 spacetimes the formalism of Roy M et al 2013 Phys. Rev. D 87 044046 with slight modifications gives the right continuum properties. We also discuss a possible test of manifoldlikeness

After a critical overview of the generalized uncertainty principle (GUP) applied to compact objects, we propose a texture of Heisenberg uncertainty principle in curved spacetimes (CHUP). CHUP allows to write down physically motivated STUR (spacetime uncertainty relations) in a generic background for a non commutative spacetime in terms of tetrad variables. In order to study possible quantum effects

We develop a complete framework for modeling general electromechanical systems in the quasi-electrostatic regime. The equations are applicable to a broad range of electrostatic problems and offer the advantage of being theoretically tractable for scaling arguments. Additionally, we show how the formalism can be used together with finite element simulations to obtain estimates for non-stationary effects

Casimir energy in presence of a weak gravitational field is discussed taking into account the issues related to energy and its conservation in a curved background. It is well-known that there are inherent difficulties in defining energy in general relativity, essentially due to its non-localizability. Using the concept of quasi-local mass and energy, it is shown that it is possible to attribute a Tolman

We present a quantum optics treatment of the near horizon behaviour of a quantum oscillator freely-falling into a pre-existing Schwarzschild black hole. We use Painlevé–Gullstrand coordinates to define a global vacuum state. In contrast to an accelerated oscillator in the Minkowski vacuum, where there is no radiation beyond an initial transient, we find that the oscillator radiates positive energy

We consider the newly proposed Bahamonde–Dialektopoulos–Levi Said (BDLS) theory, that is the Horndeski analog in the teleparallel framework and thus contains a non-minimally coupled scalar field, including higher order derivatives, that leads however to second order field equations both for the tetrad and the scalar field. This theory was mostly constructed to revive those models that were severely

In this note we present the Chandrasekhar-like transformations for the electromagnetic waves and the scalar waves in Schwarzschild spacetime, which are simpler than those known before.

It has been pointed out that the holonomy of generic extended loops is not gauge covariant. We show how to define a family of extended loops for which previous criticism does not apply. We also give sufficient conditions that extended loops must satisfy in order to yield covariant holonomies. This makes a quantum representation for Yang–Mills theories and gravity based on extended loops viable.

We introduce a new family of coherent states for loop quantum gravity, inspired by the twisted geometry parametrization. We compute their peakedness properties and compare them with the heat-kernel coherent states. They show similar features for the area and the holonomy operators, but improved peakedness in the direction of the flux. At the gauge-invariant level, the new family is built from tensor

The Geroch group is an infinite dimensional transitive group of symmetries of classical cylindrically symmetric gravitational waves which acts by non-canonical transformations on the phase space of these waves. Here this symmetry is re derived and the unique Poisson bracket on the Geroch group which makes its action on the gravitational phase space Lie–Poisson is obtained. Two possible notions of asymptotic

We examine a novel class of toy models of cosmological inhomogeneities by smoothly matching along a suitable hypersurface an arbitrary number of sections of ‘quasi flat’ inhomogeneous and anisotropic Szekeres-II models to sections of any spatially flat cosmology that can be described by the Robertson–Waker metric (including de Sitter, anti de Sitter and Minkowski spacetimes). The resulting ‘pancake’

Covtree—a partial order on certain sets of finite, unlabeled causal sets—is a manifestly covariant framework for causal set dynamics. Here, as a first step in picking out a class of physically well-motivated covtree dynamics, we study the structure of covtree and the relationship between its paths and their corresponding infinite unlabeled causal sets. We identify the paths which correspond to posts

As sensitivities improve and more detectors are added to the global network of gravitational wave observatories, calibration accuracy and precision are becoming increasingly important. Photon calibrators, relying on power-modulated auxiliary laser beams reflecting from suspended interferometer optics, enable continuous calibration by generating displacement fiducials proportional to the modulated laser

One crucial problem in relativistic astrophysics is that of the nature of black hole candidates. It is usually assumed that astrophysical black holes are described by the Schwarzschild or Kerr space–times; however, there is no direct evidence to assert this. Moreover, there are various solutions in general relativity that can be alternatives to black holes, usually called black hole mimickers. In this

The aim of the present article is to evaluate the motion of neutral and charged test particles in the vicinity of a near-extremal rotating black hole (BH) in the presence of magnetic fields. Euler–Lagrange motion equations and effective potential methods are used to characterize the motion out of the equatorial plane. Such approach is of peculiar significance if it is considered, e.g., accretion processes

This paper presents an algorithm to accelerate the evaluation of inspiral–merger–ringdown waveform models for gravitational wave data analysis. While the idea can also be applied in the time domain, here we focus on the frequency domain, which is most typically used to reduce computational cost in gravitational wave data analysis. Our work extends the idea of multibanding Vinciguerra S et al (2017

Recently, we developed effective fly-by (EFB) waveforms designed to model the burst of gravitational radiation from highly eccentric binaries. We here present a faster to evaluate frequency domain EFB waveform. The waveform is constructed through the use of asymptotic expansions of hypergeometric functions. Since the waveform is fully analytic, we study the accuracy to which the binary’s parameters

Local and global phase-space descriptions and averaging methods are used to find qualitative features of solutions for the FLRW and the Bianchi I metrics in the context of scalar field cosmologies with arbitrary potentials and arbitrary couplings to matter. The stability of the equilibrium points in a phase-space as well as the dynamics in the regime where the scalar field diverges are studied. Equilibrium

The covariant Noether charge formalism (also known as the covariant phase method) of Wald and collaborators, including its cohomological extension, is a manifestly covariant Hamiltonian formalism that, in principle, allows one to define and compute the energy, angular momenta, and chemical potentials of generic solutions of gravitational theories. However, it has been observed that for some supergravity

We show the procedure of BRST deformations of the free Chern–Simons gauge theory with the higher derivatives in antifield formalism and obtain the consistent interactions in the master action at different orders. The key ingredient in our analysis is the local BRST-cohomology which plays a crucial role in the determination of the first-order deformation, also the Jacobi identity is needed since it

We study discrete Lorentzian spectral geometry by investigating to what extent causal sets can be identified through a set of geometric invariants such as spectra. We build on previous work where it was shown that the spectra of certain operators derived from the causal matrix possess considerable but not complete power to distinguish causal sets. We find two especially successful methods for classifying

We study the continuum limit of the Benincasa–Dowker–Glaser causal set action on a causally convex compact region. In particular, we compute the action of a causal set randomly sprinkled on a small causal diamond in the presence of arbitrary curvature in various spacetime dimensions. In the continuum limit, we show that the action admits a finite limit. More importantly, the limit is composed by an