This paper presents a series of constructions providing 11-dimensional bosonic supergravity backgrounds. In particular, we treat Lorentzian manifolds given in terms of twisted products of six-dimensional Lorentzian manifolds and five-dimensional Riemannian manifolds. By considering a representative flux 4-form adapted to this setting, we analyse the system of bosonic supergravity equations and describe

We show that nontrivial topologies of the spatial section of Minkowski space–time allow for motion of a charged particle under quantum vacuum fluctuations of the electromagnetic field. This is a potentially observable effect of these fluctuations. We derive the mean squared velocity dispersion when the charged particle lies in Minkowski space–time with compact spatial sections in one, two and/or three

The TOV equation appears as the relativistic counterpart of the classical condition for hydrostatic equilibrium. In the present work we aim at showing that a generalised TOV equation also characterises the equilibrium of models endowed with other symmetries besides spherical. We apply the dual null formalism to spacetimes with two dimensional spherical, planar and hyperbolic symmetries with a perfect

In a previous paper we formulated axisymmetric general relativity in terms of real Ashtekar–Barbero variables. Here we proceed to quantize the theory. We are able to implement Thiemann’s version of the Hamiltonian constraint. This provides a 2 + 1 dimensional arena to test ideas for the dynamics of quantum gravity and opens the possibility of quantum studies of rotating black hole spacetimes.

In this introductory review, we argue that a quantum structure of space-time naturally entails a higher-spin theory, to avoid significant Lorentz violation. A suitable framework is provided by Yang–Mills matrix models, which allow to consider space-time as a physical system, which is treated on the same footing as the fields that live on it. We discuss a specific quantum space-time solution, whose

In classical general relativity, the values of fields on spacetime are uniquely determined by their values at an initial time within the domain of dependence of this initial data surface. However, it may occur that the spacetime under consideration extends beyond this domain of dependence, and fields, therefore, are not entirely determined by their initial data. This occurs, for example, in the well-known

The odd parity gravitational quasi-normal mode spectrum of black holes with non-trivial scalar hair in Horndeski gravity is investigated. We study ‘almost’ Schwarzschild black holes such that any modifications to the spacetime geometry (including the scalar field profile) are treated as small quantities. A modified Regge–Wheeler style equation for the odd parity gravitational degree of freedom is presented

We construct a quasi-inertial reference system for the atom interferometer in terms of the light-field compensation, which is equivalent to the establishment of a quantum drag-free system. The compensation considered in our approach involves feedbacks of both classical and quantum nature. As a result, it may significantly reduce the dependence of the interferometric phase shift on the atomic initial

With the arrival of the era of gravitational wave astronomy, the strong gravitational field regime will be explored soon in various aspects. In this article, we provide a general review over cylindrical systems in Einstein’s theory of general relativity. In particular, we first review the general properties, both local and global, of several important solutions of Einstein’s field equations, including

Gravitational waves from a binary with a single dynamically significant spin, notably including precessing black hole-neutron star binaries, let us constrain that binary’s properties: the two masses and the dominant black hole spin. Based on a straightforward fourier transform of ##IMG## [http://ej.iop.org/images/0264-9381/37/11/115006/cqgab7199ieqn001.gif] enabled by the corotating frame, we show

High precision measurements in various applications rely on active seismic isolation to decouple the experiment from seismic motion; therefore, closed feed-back control techniques such as sensor blending and sensor correction are commonly implemented. This paper reviews the active isolation techniques of the Albert Einstein Institute seismic attenuation system (AEI-SAS). Two approaches to improve the

We study the Schwinger effect of Gaussian correlations (quantum entanglement, discord and mutual information) of the continuous-variable two-mode squeezed states shared by Alice and Bob, paying special attention to the difference of the Schwinger effect of correlations between modes of fermion–fermion and qubit-bosonic fields studied previously. We also study the redistribution and conservativeness

The scalar–tensor theory can be formulated in both Jordan and Einstein frames, which are conformally related together with a redefinition of the scalar field. As the solution to the equation of the scalar field in the Jordan frame does not have the one-to-one correspondence with that in the Einstein frame, we give a criterion along with some specific models to check if the scalar field in the Einstein

For a particular type of k -essence scalar field, the k -essence emergent gravity metric is exactly mapped on to the Barriola–Vilenkin (BV) type metric for Schwarzschild background established by Gangopadhyay and Manna. Based on the Chandrasekhar, we report the exciting features of the time-like geodesic structure in the presence of dark energy in an emergent gravity scenario for this Barriola–Vilenkin

TianQin is a Chinese space-based observatory concept with three drag-free spacecraft orbiting the earth to observe gravitational-waves in the millihertz range. Electrical charge is inevitably accumulating on its isolated test masses which are used as the mirrors for interferometers to measure gravity variation. Charge management system based on ultraviolet (UV) light is developed to reduce the charge-induced

In this paper we review the AdS/BCFT proposal of Takayanagi for holographic description of systems with boundaries, in particular, boundary conformal field theories (BCFTs). Motivated by better understanding of the proposed duality we employ entanglement entropy as a probe of familiar properties of impurities and defects. Using the dual gravity description, we check that in two spacetime dimensions

In a Bohmian quantum cosmology scenario, we investigate some quantum effects on the evolution of the primordial universe arising from the adoption of an alternative non-trivial ordering to the quantization of the constrained Hamiltonian of a minimally coupled scalar field. The Wheeler–DeWitt equation has a contribution from the change in factor ordering, hence there are new quantum effects. We compare

We propose an approach to quantum cosmology of integrable models. To analyze the models with two dynamical variables, we introduce equivalent Hamiltonians in reduced phase spaces, which are obtained with the aid of the Faddeev–Jackiw method. Quantum dynamics of the models can be studied by using the equivalent Hamiltonians with various techniques.

We use two conformal transformations to represent field lines in the poloidal sub-manifold of Kerr space–time. The first one is based on an embedding in ##IMG## [http://ej.iop.org/images/0264-9381/37/10/105003/cqgab8399ieqn1.gif] {${\mathbb{R}}^{3}$} of a manifold which is conform to the poloidal submanifold. The second one is a planar representation using quasi-isotropic coordinates. We compare plots

We derive the modifications introduced by extra-spatial dimensions beyond the four dimensional spacetime on the macroscopic properties of neutron stars, which in turn affect the gravitational wave spectrum of their binaries. It turns out that the mass–radius relation of the neutron stars, and their tidal deformability, are affected non-trivially by the presence of extra dimensions, and can be used

We show that the Penrose inequality is satisfied for generic (in some sense) conformally flat axially symmetric nonmaximal perturbations of the Schwarzschild data. A role of horizon is played by a marginally outer trapped surface which does not have to be minimal. It has a spherical shape with respect to flat metric.

The LIGO and Virgo Scientific Collaborations have cataloged ten confident detections from binary black holes and one from binary neutron stars in their first two observing runs, which has already brought up an immense desire among the scientists to study the Universe and to extend the knowledge of astrophysics from these compact objects. One of the fundamental noise sources limiting the achievable

We show that for detections of gravitational-wave transients, constraints can be given on physical parameters of the source without using any specific astrophysical models. Relying only on fundamental principles of general relativity, we can set upper limits on the size, mass, and distance of the source solely from characteristics of the observed waveform. If the distance of the source is known from

We consider the four-dimensional Einstein–Klein–Gordon–AdS system with the conformal mass subject to the Robin boundary conditions at infinity. Above a critical value of the Robin parameter, at which the AdS spacetime goes linearly unstable, we prove existence of a family of globally regular static solutions (that we call AdS Robin solitons) and discuss their properties.

The gravitational perturbation of the Morris–Thorne wormhole has been derived by using the Newman–Penrose formalism. We apply the Teukolsky equation to the wormhole spacetime, compute the perturbed Weyl scalars, ##IMG## [http://ej.iop.org/images/0264-9381/37/10/105012/cqgab7dd8ieqn1.gif] {${{\Psi}}_{4}^{\left(1\right)}$} and obtain its master equation, decomposed in spin weighted spherical harmonics

We investigate the existence of inhomogeneous Szekeres spacetimes in Einstein-æther theory. We show that inhomogeneous solutions which can be seen as extension of the Szekeres solutions existing in Einstein-æther gravity only for a specific relation between the dimensionless coefficients which defines the coupling between the æther field with gravity. The two Szekeres classes of solutions are derived

Starting from an action principle adapted to the Newman–Penrose formalism, we provide a self-contained derivation of BMS current algebra, which includes the generalization of the Bondi mass loss formula to all BMS generators. In the spirit of the Newman–Penrose approach, infinitesimal diffeomorphisms are expressed in terms of four scalars rather than a vector field. In this framework, the on-shell

We study the teleparallel equivalent of general relativity (TEGR) with Lagrangian that includes the flat (inertial) spin connection and that is evidently invariant with respect to local Lorentz rotations. Applying directly the Noether theorem, we construct new expressions for conserved currents and related superpotentials. They are covariant both under coordinate transformations and local Lorentz rotations

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We point out that the symplectic structure, written in terms of the Sen–Ashtekar–Immirzi–Barbero variables, of a spacetime admitting an isolated horizon as the inner boundary, involves a positive constant parameter, say σ , if γ ≠ ± i , where γ is the Barbero–Immirzi parameter. The parameter σ represents the rescaling freedom that characterizes the equivalence class of null generators of the isolated

Given that gravitational waves are the future probes of the Universe, it is important to test various physical effects of these on matter. This article explores the first-order perturbation, caused by a planar gravitational wave, on massless scalar and chiral fermions. We find a new propagating mode for the perturbed fields with a new dispersion relation by solving inhomogeneous differential equations

It is proposed that if quantum states of space-time are coherent on null surfaces, holographic Planck-scale fluctuations of inflationary horizons dominate the formation of primordial scalar curvature perturbations. It is shown that the reduction of quantum states on nearly-spherical emergent horizon surfaces around each observer creates a distinctive pattern whose correlations in the angular domain

We present an analysis of the null geodesics of the static, spherically symmetric, vacuum solution to the equations of conformal (Weyl) gravity. We classify the full range of exotic spacetimes arising from the parameter space of the metric. The nature of various notable features of these spacetimes is investigated including light spheres, horizons and physical singularities.

We extend the Ori–Thorne–Kesden procedure to consistently describe the non-quasi-circular transition around the ISCO from inspiral to plunge into a black hole of arbitrary spin, including near-extremal. We identify that for moderate or high spins the transition is governed by the Painlevé transcendent equation of the first kind while for extremely high spins it is governed by a self-similar solution

We develop a numerical method to investigate the semiclassical limit of spin foam amplitudes with many vertices. We test it using the Ponzano–Regge model, a spin foam model for three-dimensional euclidean gravity, and a transition amplitude with three vertices. We study the summation over bulk spins, and we identify the stationary phase points that dominate it and that correspond to classical geometries

It is shown here in the framework of standard general relativity that the gravitational potential in static spacetime, equivalently the redshift factor, inside any kind of matter, can be derived from maximum entropy principle. It is used only the Hamiltonian constraint, without further invoking Einstein’s equations or any new principle. The Newtonian potential arises from the same procedure.

The increasing precision of spacecraft radiometric tracking data experienced in the last number of years, coupled with the huge amount of data collected and the long baselines of the available datasets, has made the direct observation of Solar System dynamics possible, and in particular relativistic effects, through the measurement of some key parameters as the post-Newtonian parameters, the Nordtvedt

The concept of a fake particle, or ‘fakeon’, allows us to make sense of quantum gravity as an ultraviolet complete theory, by renouncing causality at very small distances. We investigate whether the violation of microcausality can be amplified or detected in the most common settings. We show that it is actually short range for all practical purposes. Due to our experimental limitations, the violation

It is known that a rotating black hole immersed in a magnetic field can selectively accrete charges of one sign and repel charges of the opposite sign. This gives rise to a magnetic moment of the form ##IMG## [http://ej.iop.org/images/0264-9381/37/9/095002/cqgab7d80ieqn1.gif] {${\mathcal{M}}_{\mathrm{B}\mathrm{H}}=\frac{Q}{{m}_{\mathrm{B}\mathrm{H}}}\;{S}_{\mathrm{B}\mathrm{H}}$} where Q is the black

In this article we consider physical states in the hypercuboidal truncation of the EPRL-FK spin foam model for Euclidean quantum gravity. In particular, these states are defined on graphs which allow considering the entanglement entropy (EE) associated to the bipartition of space. We compute the EE numerically for some examples, and find that it depends on the coupling constant α within the theory

Recently, Tsupko et al have put forward the very interesting proposal to use the shadows of high-redshift supermassive black holes (SMBHs) as standard rulers. This would in principle allow us to probe the expansion history within a redshift range which would otherwise be challenging to access. In this note, we critically examine this proposal, and identify a number of important issues which had been

It was recently shown that the volume operator of loop quantum cosmology (LQC) and all its positive powers are ill-defined on physical states. In this paper, we investigate how it effects predictions of cosmic microwave background (CMB) power spectra obtained within dressed metric approach for which expectations values of â are the key element. We find that almost every step in the procedure is ill-defined

There are at least two ways to encode gravity into geometry: Einstein’s general theory of relativity (GR) for the metric tensor, and teleparallel gravity, where torsion as opposed to curvature encodes the dynamics of the gravitational degrees of freedom. The main purpose of the paper is to explore the relation between loop gravity and teleparallel gravity. We argue that these two formulations of gravity

By numerical simulation, we compare the performance of four speedmeter interferometer configurations with potential application in future gravitational wave detectors. In the absence of optical loss, all four configurations can be adjusted to yield the same sensitivity in a fair comparison. Once we introduce a degree of practicality in the form of lossy optics and mode mismatch, however, the situation

In this paper we elevate the formalism for off-shell Abbott–Deser–Tekin (ADT) conserved charges in the presence of arbitrary matter fields to including the internal gauge transformation, when the gauge fields are present. For this purpose, we resort to exact symmetry, and the symmetry generator is combined by diffeomorphism and internal gauge transformation. For universality, we consider an apparently

We derive the uncertainty principle for a Dirac fermion in a torsion field obeying the Hehl–Datta (HD) equation. We find out how the non-linear term in the HD equation modifies the uncertainty principle and how it compares with the generalized uncertainty principle (GUP). We first discuss that there should be a correction factor to the Heisenberg uncertainty principle (HUP) when torsional effects are

We study the canonical Hamiltonian analysis of gauge theories in the presence of boundaries. While the implementation of Dirac’s programme in the presence of boundaries, as put forward by Regge and Teitelboim, is not new, there are some instances in which this formalism is incomplete. Here we propose an extension to the Dirac formalism—together with the Regge–Teitelboim strategy—that includes generic

Pulsar timing arrays have yet to convincingly observe gravitational waves. Some time ago it was pointed out by one of the authors that a dramatic enhancement of the signal would take place for particular values of the angle subtended by the source and the observed pulsar. This enhancement is due to the fact that waves propagate in a Friedmann–Lemaitre–Robertson–Walker metric where, contrary to some

It is well known that a superfluid rotates by forming an array of quantized vortices. A relativistic formulation for superfluid vortex dynamics is required for a range of problems in astrophysics and cosmology, from neutron star interiors and radio pulsar glitches to possible dark matter condensates on galactic scales. This paper develops a formalism for such systems, extending the well-established

We consider a non-minimally coupled curvature–matter gravity model (NMC) with a Weyl connection, a theory referred to as non-minimally coupled Weyl connection gravity (NMCWCG). The Weyl connection is an affine connection that is not compatible with the metric, and involves a vector field. Assuming a vacuum expectation value for the vector field and a matter Lagrangian that only contains the contributions

Despite their potential importance for understanding astrophysical jets, physically realistic exact solutions for magnetospheres around Kerr black holes have not been found, even in the force-free approximation. Instead approximate analytical solutions such as the Blandford–Znajek (split-)monopole, as well as numerical solutions, have been constructed. In this paper we consider a new approach to the

In the first part of this paper we consider expanding vacuum cosmological spacetimes with a free T N -action. Among them, we give evidence that Gowdy spacetimes have AVTD (asymptotic velocity term dominated) behavior for their initial geometry, in any dimension. We then give sufficient conditions to reach a similar conclusion about a T 2 -invariant four dimensional nonGowdy spacetime. In the second

We present a gauge-invariant treatment of singularity resolution using loop quantum gravity techniques with respect to local SU(2) transformations. Our analysis reveals many novel features of quantum geometry which were till now hidden in models based on non-gauge-invariant discretizations. Quantum geometric effects resolve the big bang singularity replacing it with a non-singular bounce when spacetime

With the first direct detection of gravitational waves, the advanced laser interferometer gravitational-wave observatory (LIGO) has initiated a new field of astronomy by providing an alternative means of sensing the universe. The extreme sensitivity required to make such detections is achieved through exquisite isolation of all sensitive components of LIGO from non-gravitational-wave disturbances.