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Recently, there has been significant interest regarding the regularization of a D→4$D\rightarrow 4$ limit of Einstein–Gauss–Bonnet (EGB) gravity. This regularization involves re‐scaling the Gauss–Bonnet (GB) coupling constant as α/(D−4)$\alpha /(D-4)$, which bypasses Lovelock's theorem and avoids Ostrogradsky instability. A noteworthy observation is that the maximally or spherically symmetric solutions for all the regularized gravities coincide in the 4D$4D$ scenario. Considering this, the wormhole solutions in the galactic halos are investigated based on three different choices of dark matter (DM) profiles, such as Universal Rotation Curve, Navarro–Frenk–White, and Scalar Field Dark Matter with the framework of 4D$4D$ EGB gravity. Also, the Karmarkar condition is used to find the exact solutions for the shape functions under different non‐constant redshift functions. The energy conditions for each DM profile are discussed and the influence of GB coefficient α$\alpha$ in violating energy conditions are noticed, especially null energy conditions. Further, some physical features of wormholes, viz. complexity factor, active gravitational mass, total gravitational energy, and embedding diagrams, have been explored. [ABSTRACT FROM AUTHOR]

Multiply lensed images of a same source experience a relative time delay in the arrival of photons due to the path length difference and the different gravitational potentials the photons travel through. This effect can be used to measure absolute distances and the Hubble constant ( H 0 ) and is known as time-delay cosmography. The method is independent of the local distance ladder and early-universe physics and provides a precise and competitive measurement of H 0 . With upcoming observatories, time-delay cosmography can provide a 1% precision measurement of H 0 and can decisively shed light on the current reported 'Hubble tension'. This manuscript details the general methodology developed over the past decades in time-delay cosmography, discusses recent advances and results, and, foremost, provides a foundation and outlook for the next decade in providing accurate and ever more precise measurements with increased sample size and improved observational techniques. [ABSTRACT FROM AUTHOR]

We present time-dependent nova outburst models with optically thick winds for 1.2 and 1.35 |$\, M_{\odot }$| white dwarfs (WDs) with a mass-accretion rate of |$5 \times 10^{-9}\, M_{\odot }$|  yr−1 and for a 1.3 |$\, M_{\odot }$| WD with |$2 \times 10^{-9}\, M_{\odot }$|  yr−1. The X-ray flash occurs 11 d before the optical peak of the 1.2 |$\, M_{\odot }$| WD and 2.5 d before the peak of the 1.3 |$\, M_{\odot }$| WD. The wind mass-loss rate of the 1.2 |$\, M_{\odot }$| WD (1.3 |$\, M_{\odot }$| WD) reaches a peak of |$6.4 \times 10^{-5}\, M_{\odot }$| yr−1 (⁠|$7.4 \times 10^{-5}\, M_{\odot }$| yr−1) at the epoch of the maximum photospheric expansion with the lowest photospheric temperature of log  T ph (K) = 4.33 (4.35). The nuclear energy generated during the outburst is lost in the form of radiation (61% for the 1.2 |$\, M_{\odot }$| WD; 47% for the 1.3 |$\, M_{\odot }$| WD), gravitational energy of ejecta (39%; 52%), and kinetic energy of the wind (0.28%; 0.29%). We found an empirical relation for fast novae between the time to optical maximum from the outburst t peak and the expansion timescale τexp. With this relation, we are able to predict the time to optical maximum t peak from the ignition model (at t = 0) without following a time-consuming nova wind evolution. [ABSTRACT FROM AUTHOR]

Diffusion of atoms and molecules is usually driven by concentration gradients, with the influence of gravitational energy being negligible. However, for alloying components operating at exceptional rotational speeds, such as engine blades, the resulting centrifugal force significantly impacts element distribution. In hypergravity fields, the gravitational potential becomes comparable to the chemical potential, and these two factors jointly determine the diffusion process in solid solutions. This study establishes a theoretical model to quantify the influence of hypergravity on element diffusion in solids, analogous to centrifugal environments in engineering applications. Element diffusion under hypergravity, combined with different boundary conditions, is analyzed. It is found that gravitational energy in a hypergravity field promotes element diffusion when both are in the same direction. In particular, the effect of the hypergravity field on the diffusion process is determined by the difference between the density of diffusing atoms and one-third of the density of the solid substrate. This newly established model provides a valuable tool for assessing element diffusion in solids under extreme hypergravity conditions. [ABSTRACT FROM AUTHOR]

In order to develop a complete theory of star formation, one essentially needs to know two things: what collapses and how long it takes. This is the second paper in a series, where we query how long a parcel of gas takes to collapse and the process it undergoes. We embed pseudo-Lagrangian tracer particles in simulations of collapsing molecular clouds, identify the particles that end in dense knots, and then examine the collapse history of the gas. We find a nearly universal behaviour of cruise-then-collapse, wherein a core stays at intermediate densities for a significant fraction of its life before finally collapsing. We identify time immediately before each core collapses, |$t_{\rm {sing}}$|⁠ , and examine how it transitions to high density. We find that the time to collapse is uniformly distributed between |$0.25 t_{\rm {ff}}$| and the end of the simulation at |$\sim\!\! 1 t_{\rm {ff}}$|⁠ , and that the duration of collapse is universally short, |$\Delta t \sim 0.1 t_{\rm {ff}}$|⁠ , where |$t_{\rm {ff}}$| is the free-fall time at the mean density. We describe the collapse in three stages: collection, hardening, and singularity. Collection sweeps low-density gas into moderate density. Hardening brings kinetic and gravitational energies into quasi-equipartition. Singularity is the free-fall collapse, forming an envelope in rough energy balance and central overdensity in |$\sim\!\! 0.1 t_{\rm {ff}}$|⁠. [ABSTRACT FROM AUTHOR]

Context. The vast majority of close binaries containing a compact object, including the progenitors of supernovae Ia and at least a substantial fraction of all accreting black holes in the Galaxy, form through common-envelope (CE) evolution. Despite this importance, we struggle to even understand the energy budget of CE evolution. For decades, observed long-period post-CE binaries have been interpreted as evidence of additional energies contributing during CE evolution. We have recently shown that this argument is based on simplified assumptions for all long-period post-CE binaries containing massive white dwarfs (WDs). The only remaining post-CE binary star that has been claimed to require contributions from additional energy sources to understand its formation is KOI 3278. Aims. Here, we address in detail the potential evolutionary history of KOI 3278. In particular, we investigate whether extra energy sources, such as recombination energy, are indeed required to explain its existence. Methods. We used the 1D stellar evolution code MESA to carry out binary evolution simulations and searched for potential formation pathways for KOI 3278 that are able to explain its observed properties. Results. We find that KOI 3278 can be explained if the WD progenitor filled its Roche lobe during a helium shell flash. In this case, the orbital period of KOI 3278 can be reproduced if the CE binding energy is calculated taking into account gravitational energy and thermodynamic internal energy. While the CE evolution that led to the formation of KOI 3278 must have been efficient – that is, most of the available orbital energy must have been used to unbind the CE – recombination energy is not required. Conclusions. We conclude that currently not a single observed post-CE binary requires one to assume that energy sources other than gravitational and thermodynamic energy are contributing to CE evolution. KOI 3278, however, remains an intriguing post-CE binary as, unlike its siblings, understanding its existence requires highly efficient CE ejection. [ABSTRACT FROM AUTHOR]

A quantum well (QW) diode that is capable of emitting light is also capable of absorbing light. In particular, the QW diode has broad electroluminescence and responsivity spectra and thus, a distinct spectral overlap exists, enabling the establishment of light communication using two identical QW diodes, namely, one as the transmitter and the other as the receiver. Here, we demonstrate a time-division multiplexing (TDM) wireless light communication using two identical green QW diodes that are defined by software as transmitter or receiver to achieve real-time underwater data transmission via the same optical channel. To further exploit this dual emission-detection characteristics, we unite energy conservation, gravitational field and energy diagram theory to arrive the conclusion that the gravitational field may play a key role in the irreversibility between light emission and detection of the QW diode. [ABSTRACT FROM AUTHOR]

With the rapid development of new-generation artificial intelligence and Internet of Things technology, mobile robot technology has been widely used in various fields. Among them, the autonomous path-planning technology of mobile robots is one of the cores for realizing their autonomous driving and obstacle avoidance. This study conducts an in-depth discussion on the real-time and dynamic obstacle avoidance capabilities of mobile robot path planning. First, we proposed a preprocessing method for obstacles in the grid map, focusing on the closed processing of the internal space of concave obstacles to ensure the feasibility of the path while effectively reducing the number of grid nodes searched by the A* algorithm, thereby improving path search efficiency. Secondly, in order to achieve static global path planning, this study adopts the A algorithm. However, in practice, algorithm A has problems such as a large number of node traversals, low search efficiency, redundant path nodes, and uneven turning angles. To solve these problems, we optimized the A* algorithm, focusing on optimizing the heuristic function and weight coefficient to reduce the number of node traversals and improve search efficiency. In addition, we use the Bezier curve method to smooth the path and remove redundant nodes, thereby reducing the turning angle. Then, in order to achieve dynamic local path planning, this study adopts the artificial potential field method. However, the artificial potential field method has the problems of unreachable target points and local minima. In order to solve these problems, we optimized the repulsion field so that the target point is at the lowest point of the global energy of the gravitational field and the repulsive field and eliminated the local optimal point. Finally, for the path-planning problem of mobile robots in dynamic environments, this study proposes a hybrid path-planning method based on a combination of the improved A* algorithm and the artificial potential field method. In this study, we not only focus on the efficiency of mobile robot path planning and real-time dynamic obstacle avoidance capabilities but also pay special attention to the symmetry of the final path. By introducing symmetry, we can more intuitively judge whether the path is close to the optimal state. Symmetry is an important criterion for us to evaluate the performance of the final path. [ABSTRACT FROM AUTHOR]

It is often noted that the Earth is slightly oblate rather than spherical, but the calculation of the Earth's eccentricity can be challenging. Here, we calculate it by minimizing the sum of the Earth's gravitational potential energy and its centrifugal potential energy. The Earth's gravitational potential energy can be derived with the help of the Green's function of the Laplace operator in oblate spheroidal coordinates. Under the assumption of a homogeneous planet, we obtain an analytic relationship for the Earth's eccentricity that was first derived by Maclaurin in 1742 and is about 13 percent larger than the observed value. Better agreement with observation is obtained by assuming that the Earth's core is about twice the density of the mantle, which reduces the Earth's moment of inertia. This exercise can provide practice in analyzing gravitational systems in spheroidal coordinates; the problem may also be relevant for other gravitating and rotating bodies, such as stars and galaxies. Editor's note: This short paper presents a new derivation of the Earth's eccentricity using the minimization of the Earth's total energy that includes both the gravitational and the centrifugal energies. It employs the Green's function of the Laplace operator, a mathematical tool that is commonly used, for instance in electrostatics. Appropriate for advanced undergraduate mechanics courses or for illustrating the utility of Green's functions. [ABSTRACT FROM AUTHOR]

In the field of theoretical physics, the fundamental characteristics and evolutionary mechanism of dark energy remain a subject of ongoing enquiry. While the simplest explanation for dark energy within General Relativity Theory is the cosmological constant, this concept faces a significant challenge known as the fine-tuning problem. In this study, we adopt an alternative approach, where we attribute the evolution of dark energy to the gravitational sector rather than the matter source. We explore the recently proposed theory of gravity known as modified symmetric teleparallel gravity, f (Q) , in which gravitational interactions are governed by the non-metricity term Q. Within this manuscript, we consider f (Q) = α Q β that incorporates nonlinear forms of the non-metricity scalar, where α and β are free model parameters. Subsequently, we determine the values of these model parameters that align with the observed values of cosmographic parameters. Our analysis delves into the behavior of various cosmological parameters, including the deceleration parameter, density, and equation of state parameters, as well as the cosmological distances for our cosmological model. [ABSTRACT FROM AUTHOR]

This study explores nonlinear development of the magnetized Rayleigh–Taylor instability (RTI) in a prominence-corona transition region. Using a two-fluid model of a partially ionized plasma, we compare RTI simulations for several different magnetic field configurations. We follow prior descriptions of the numerical prominence model (Popescu Braileanu et al. 2021 Astron. Astrophys.646, A93 (doi:10.1051/0004-6361/202039053), Popescu Braileanu et al. 2021 Astron. Astrophys.650, A181 (doi:10.1051/0004-6361/202140425) and Popescu Braileanu et al. 2023 Astron. Astrophys.670, A31 (doi:10.1051/0004-6361/202142996)) and explore the charged-neutral fluid coupling and plasma heating in a two-dimensional mixing layer for different magnetic field configurations. We also investigate how the shear in magnetic field surrounding a prominence may impact the release of the gravitational potential energy of the prominence material. We show that the flow decoupling is strongest in the plane normal to the direction of the magnetic field, where neutral pressure gradients drive ion-neutral drifts and frictional heating is balanced by adiabatic cooling of the expanding prominence material. We also show that magnetic field within the mixing plane can lead to faster nonlinear release of the gravitational energy driving the RTI, while more efficiently heating the plasma via viscous dissipation of associated plasma flows. We relate the computational results to potential observables by highlighting how integrating over under-resolved two-fluid sub-structure may lead to misinterpretation of observational data. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

A gravity compensation (GC) device compensates for the torque originating from a constant mass or payload, which occupies a large part of the capacity and energy consumption of an actuator on the joint. Adapting a GC device can reduce energy consumption and capacity of the actuator. A GC device comprises an energy-storage component and a motion-converting mechanism. The energy storage component stores and releases energy according to the change in gravitational energy as the mass of the joint rotates. The motion-converting mechanism matches the energy from the energy storage component to the gravitational energy of the rotating mass. The majority of GC devices use springs as the energy storage component, and they are connected to the body by motion-converting mechanisms, such as gears and slide cranks. A GC device that uses magnetic energy as an energy storage component was proposed in this study. It uses noncontact permanent magnets (PMs) as energy storage components. It is designed to have a simple structure and compact size, and can be easily connected to the actuator module, similar to commercial gear reducers. It comprises two identical structures, consisting of one yoke and two PMs. The two structures are assembled as the PMs face each other and generate attractive and repulsive forces depending on the relative angle between the two facing PMs. The shapes of the PMs were determined to generate a sinusoidal torque profile to compensate for the gravitational torque by a mass. The designed mechanism is verified through simulations and experiments. [ABSTRACT FROM AUTHOR]

The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. The cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. The outflows from the central engine tightly couple with the surrounding gaseous medium and provide the dominant heating source, preventing runaway cooling. Every major modern hydrodynamical simulation suite now includes a prescription for AGN feedback to reproduce the realistic populations of galaxies. However, the mechanisms governing the feeding/feedback cycle between the central black holes and their surrounding galaxies and halos are still poorly understood. Galaxy groups are uniquely suited to constrain the mechanisms governing the cooling–heating balance, as the energy supplied by the central AGN can exceed the gravitational binding energy of halo gas particles. Here, we provide a brief overview of our knowledge of the impact of AGN on the hot atmospheres of galaxy groups, with a specific focus on the thermodynamic profiles of the groups. We then present our on-going efforts to improve on the implementation of AGN feedback in galaxy evolution models by providing precise measurements of the properties of galaxy groups. We introduce the XMM-Newton Group AGN Project (X-GAP), a large program on XMM-Newton targeting a sample of 49 galaxy groups out to R 500 c . [ABSTRACT FROM AUTHOR]

A mechanism for the ejection of relativistic jets from slim disks is studied. Since radiation pressure is dominant in the slim disk, radiative energy flows along the pressure gradient in the vertical direction. The divergence of the radiative flux tells us that the flow of radiative energy from a bottom layer near the equatorial plane is absorbed by another layer above the boundary surface. The absorbed energy accumulates in the upper layer as the matter advances inward, and calculations show that the specific energy of the flow in the upper layer can be as large as ∼ c 2 near the black hole when the accretion rate through the upper layer is relatively low. Since the specific energy ∼ c 2 is much larger than the gravitational energy, the height of the upper layer could significantly increase then. Hence, the innermost part of the upper layer after almost all the angular momentum has been removed could have a much greater height than the size of the black hole, and the flow could collide with itself around the central axis of the disk, bouncing back from the axis while simultaneously expanding along it. The flow is expected to go outward along the central axis and to become supersonic due to the change in its cross section, finally producing relativistic jets. [ABSTRACT FROM AUTHOR]

Deformable linear objects (DLOs), such as rods, cables, and ropes, play important roles in daily life. However, manipulation of DLOs is challenging as large geometrically nonlinear deformations may occur during the manipulation process. This problem is made even more difficult as the different deformation modes (e.g., stretching, bending, and twisting) may result in elastic instabilities during manipulation. In this paper, we formulate a physics-guided data-driven method to solve a challenging manipulation task—accurately deploying a DLO (an elastic rod) onto a rigid substrate along various prescribed patterns. Our framework combines machine learning, scaling analysis, and physical simulations to develop a physics-based neural controller for deployment. We explore the complex interplay between the gravitational and elastic energies of the manipulated DLO and obtain a control method for DLO deployment that is robust against friction and material properties. Out of the numerous geometrical and material properties of the rod and substrate, we show that only three non-dimensional parameters are needed to describe the deployment process with physical analysis. Therefore, the essence of the controlling law for the manipulation task can be constructed with a low-dimensional model, drastically increasing the computation speed. The effectiveness of our optimal control scheme is shown through a comprehensive robotic case study comparing against a heuristic control method for deploying rods for a wide variety of patterns. In addition to this, we also showcase the practicality of our control scheme by having a robot accomplish challenging high-level tasks such as mimicking human handwriting, cable placement, and tying knots. [ABSTRACT FROM AUTHOR]

In this work, the spreading of a small sessile drop on a smooth, flat surface has been analyzed. A comprehensive energy balance was developed that consists of wetting energy, air-liquid interfacial energy, gravitational energy, and heat due to flow dissipation. The net change in these energies is predicted to vary widely with the wettability of the solid surface. On the least wettable surfaces, energy released by contraction of the air-liquid interface drives spreading. On the most wettable surfaces, spreading is powered by wetting energy released from the advancing contact line. On surfaces with intermediate wettability, spreading is fueled by a combination of energies released from both the air-liquid interface and the contact line. Generally, gravitational energy is minuscule compared to the other energies. Overall, the model suggests that spreading is exothermic, as expected for a spontaneous process. Small liquid drops with a wide variety of surface tension and density are anticipated to give similar results. [ABSTRACT FROM AUTHOR]

Gas‐particle aero‐type cyclones have revolutionized biochemical processes, engineering industries, and environmental pollution protection by effectively separating particles from gas. These devices rely on gravitational energy and centrifugal force to dissipate particle phase energy, but achieving optimal energy efficiency while minimizing pressure drop remains challenging. This has led to the development of various cyclone designs in commercial industries, each with unique energy efficiency characteristics. The intricate gas‐particle flow inside cyclones is a critical issue impacted by cyclone geometry, operating conditions, and media parameters. Advanced numerical simulations have been employed to understand this complex flow pattern better, offering researchers valuable insights into the mechanisms of different cyclone separators. This comprehensive review explores the available numerical methods in the literature on cyclones and their corresponding validations. Computational numerical modeling is a promising technique for predicting cyclone energy efficiency, gas‐particle behavior, and overall performance. This investigation delves into the progress and numerical forms of gas‐particle flow cyclones, examining how different parameters impact cyclone performance and flow patterns within the two‐phase flow. The future developments and challenges that may further promote the development of aero‐type cyclone separators, providing theory and engineering support for future cyclone designs, are also covered. As a result, it can confidently be reported that aero‐type cyclone separators remain a critical component in various industrial sectors, offering energy‐efficient solutions for mitigating environmental pollutants and gas‐particle separation systems. With continued development and research, these devices will undoubtedly shape the future of energy processes and engineering industries, ushering in a new era of sustainability and efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we investigate relations or differences among various conserved quantities which involve the matter Energy Momentum Tensor (EMT) in general relativity. These quantities include the energy with Einstein's pseudo EMT, the generalized Komar integral, or the ADM energy, all of which can be derived from Noether's second theorem, as well as an extra conserved charge recently proposed in general relativity. For detailed analyses, we apply definitions of these charges to a system of free massive particles. We employ the post-Newtonian (PN) expansion to make physical interpretations. We find that the generalized Komar integral is not conserved at the first non-trivial order in the PN expansion due to non-zero contributions at spatial boundaries, while the energy with Einstein's pseudo EMT at this order agrees with a total energy of massive particles with gravitational interactions through the Newtonian potential, and thus is conserved. In addition, this total energy is shown to be identical to the ADM energy not only at this order but also all orders in the PN expansion. We next calculate an extra conserved charge for the system of massive particles, at all orders in the PN expansion, which turns out to be a total number of particles. We call it a gravitational charge, since it is clearly different from the total energy. We finally discuss an implication from a fact that there exist two conserved quantities, energy and gravitational charge, in general relativity. [ABSTRACT FROM AUTHOR]

In the face of increasing global energy demand and growing dependence on renewable sources, there exists a compelling need for innovative energy storage solutions. Traditional methods, while effective, face limitations in terms of scalability, adaptability, cost, and environmental impact. This urgency is particularly evident in the intermittent nature of renewable sources like solar and wind. To bridge the gap between energy production and demand, there is a compelling call for innovative storage technologies that not only overcome current limitations but also align with the evolving landscape of sustainable energy solutions. This short communication introduces a preliminary design concept for an innovative energy storage system (ESS) designed to store excess electrical energy generated during off‐peak periods, particularly from renewable sources, for subsequent retrieval during peak demand. The proposed storage solution capitalizes on the principles of electromagnetic induction and gravitational potential energy, providing an inventive and sustainable approach to energy storage. The proposed ESS can promise a swift and effective storage solution, particularly for remote, off‐grid areas, boasting high energy autonomy, minimal maintenance requirements, and negligible environmental impact. The preliminary design specifics and distinctive features of the proposed ESS are outlined, along with a discussion on the challenges associated with its development and implementation. [ABSTRACT FROM AUTHOR]

We considered the generation of gravitational waves by the binary system associated with a wormhole. In the Newtonian limit, the gravitational potential of a wormhole requires the effective mass of the wormhole taking into account radial tension effects. This definition allows us to derive gravitational wave production in homogeneous and heterogeneous binary systems. Therefore, we studied gravitational waves generation by orbiting wormhole–wormhole and wormhole–black hole binary systems before coalescence. Cases involving negative mass require more careful handling. We also calculated the energy loss to gravitational radiation by a particle orbiting around the wormhole and by a particle moving straight through the wormhole mouth, respectively. [ABSTRACT FROM AUTHOR]

This paper deals with the thermodynamics of gravitational radiation arising from the Bondi-Sachs space-time. The equation of state found allows us to conclude that the dependence of the energy density on the temperature is a quadratic power of the latter. Such a conclusion is possible once the consequences of the first law of thermodynamics are analyzed. Then, in analogy to electromagnetic radiation, the same approach used by Planck to obtain the quantum of energy of the gravitational radiation is proposed. An energy for the graviton proportional to the cubic frequency is found. The graviton is here understood as the quantum of gravitational energy. [ABSTRACT FROM AUTHOR]

We obtain two equations (following from two different approaches) for the density profile in a self-gravitating polytropic cylindrically symmetric and rotating turbulent gas disc. The adopted physical picture is appropriate to describe the conditions near to the cloud core where the equation of state of the gas changes from isothermal (in the outer cloud layers) to one of 'hard polytrope', and the symmetry changes from spherical to cylindrical. On the assumption of steady state, as the accreting matter passes through all spatial scales, we show that the total energy per unit mass is an invariant with respect to the fluid flow. The obtained equation describes the balance of the kinetic, thermal, and gravitational energy of a fluid element. We also introduce a method for approximating density profile solutions (in a power-law form), leading to the emergence of three different regimes. We apply, as well, dynamical analysis of the motion of a fluid element. Only one of the regimes is in accordance with the two approaches (energy and force balance). It corresponds to a density profile of a slope −2, polytropic exponent 3/2, and sub-Keplerian rotation of the disc, when the gravity is balanced by the thermal pressure. It also matches with some observations and numerical works and, in particular, leads to a second power-law tail (of a slope ∼−1) of the density distribution function in dense, self-gravitating cloud regions. [ABSTRACT FROM AUTHOR]

The definitions of stored gravitational energy are given. The value of the limited gravitational energy of two massive mutually nonpenetrating balls is calculated. It is established that the stored gravitational energy is always positive. A formula is presented for the maximum possible gravitational energy of two massive balls, which can be used to estimate the energy of the merger of space objects, in particular, gaseous, dusty, and plasma, as well as for ballistic calculations of space flights. [ABSTRACT FROM AUTHOR]

Motivated by the generation of exceptionally large gravito-elastic waves during the Hunga Tonga–Hunga Ha'apai explosion of 15 January 2022, we examine theoretically the nature of the main air wave branch G R 0 , whose undispersed celerity, ∼ 313 m/s, suggests that it may represent a "tsunami" of the atmospheric column for an effective thickness H eff ≈ 10 km. However, we find that its potential energy is about 90% elastic across a wide frequency band, thus negating the widely held perception that it constitutes an oscillation between kinetic and gravitational energy. Based on the systematic study of the effect of finite compressibility on the dispersion and potential energy of a classic oceanic tsunami, we confirm that this feature of the branch G R 0 stems from the similarity between its celerity and the average speed of sound in the atmosphere. We then show that this similarity is not fortuitous, but rather expected for a perfect gas, which, we conclude, cannot sustain "tsunamis", i.e., oscillations between kinetic and gravitational energy. [ABSTRACT FROM AUTHOR]

The concept and definitions of the energy–momentum and angular momentum of the gravitational field in the teleparallel equivalent of general relativity (TEGR) are reviewed. The importance of these definitions is justified by three major reasons. First, the TEGR is a well established and widely accepted formulation of the gravitational field, whose basic field strength is the torsion tensor of the Weitzenböck connection. Second, in the phase space of the TEGR there exists an algebra of the Poincaré group. Not only the definitions of the gravitational energy–momentum and 4‐angular momentum satisfy this algebra, but also the first class constraints related to these definitions satisfy the algebra. And third, numerous applications of these definitions lead to physically consistent results. These definitions follow from a well established Hamiltonian formulation, and rely on the idea of localization of the gravitational energy. In this review, the concept of localizability of the gravitational energy is revisited, in light of results obtained in recent years. The behavior of free particles is studied in the space–time of plane fronted gravitational waves (pp‐waves). Free particles are here understood as particles that are not subject to external forces other than the gravitational acceleration due to pp‐waves. Since these particles acquire or loose kinetic energy locally, the transfer of energy from or to the gravitational field must also be localized. This theoretical result is considered an important and definite argument in favor of the localization of the gravitational energy–momentum, and by extension, of the gravitational 4‐angular momentum. [ABSTRACT FROM AUTHOR]

In order to resolve several theoretical and practical flaws in general relativity GR, a variety of modified theories of gravity have been proposed. One exciting strategy is to modify gravity's geometrical nature. The teleparallel theory of gravity accomplishes this. In this paper, we study the gravitational energy GE and gravitational pressure of stringy charged black holes SCBH namely within the basic framework of the teleparallel equivalent of general relativity GR. We determine GE bounded by the event horizon of the black hole BH and the radial pressure RP over it. Furthermore, we examine the gravitational entropy of SCBH which is affected by BH's mass m and charge Q. [ABSTRACT FROM AUTHOR]

The main purpose of this study is to review the Schenberg resonant antenna transfer function and to recalculate the antenna design strain sensitivity for gravitational waves. We consider the spherical antenna with six transducers in the semi dodecahedral configuration. When coupled to the antenna, the transducer-sphere system will work as a mass-spring system with three masses. The first one is the antenna effective mass for each quadrupole mode, the second one is the mass of the mechanical structure of the transducer first mechanical mode and the third one is the effective mass of the transducer membrane that makes one of the transducer microwave cavity walls. All the calculations are done for the degenerate (all the sphere quadrupole mode frequencies equal) and non-degenerate sphere cases. We have come to the conclusion that the "ultimate" sensitivity of an advanced version of Schenberg antenna (aSchenberg) is around the standard quantum limit (although the parametric transducers used could, in principle, surpass this limit). However, this sensitivity, in the frequency range where Schenberg operates, has already been achieved by the two aLIGOs in the O3 run, therefore, the only reasonable justification for remounting the Schenberg antenna and trying to place it in the sensitivity of the standard quantum limit would be to detect gravitational waves with another physical principle, different from the one used by laser interferometers. This other physical principle would be the absorption of the gravitational wave energy by a resonant mass like Schenberg. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) are widely believed to be one of the promising acceleration sites of ultrahigh-energy cosmic rays (CRs). Essentially, AGNs are powered by the gravitational energy of matter falling into supermassive black holes. However, the conversion efficiency of gravitational to kinetic energy of CRs in AGNs, which is defined as the baryon loading factor η p , is not well known yet. After being accelerated, high-energy CRs could escape the host galaxy and enter the intracluster medium (ICM). These CRs can be confined within the galaxy cluster and produce γ -rays and neutrinos through proton–proton collisions with the ICM. In this paper, we study the diffusion of CRs in galaxy clusters and calculate the diffuse neutrino flux from the galaxy cluster population. Using the latest upper limits on the cumulative unresolved TeV–PeV neutrino flux from galaxy clusters posed by the IceCube Neutrino Observatory, we derive the upper limit of the average baryon loading factor as η p,grav ≲ 2 × 10−3 − 0.1 for the population of galaxy clusters. This constraint is more stringent than the one obtained from γ -ray observation on the Coma cluster. [ABSTRACT FROM AUTHOR]

The idea of quantum mechanical vacuum energy contributing to the cosmological vacuum energy density is not new. However, despite the persisting cosmological constant problem, few investigations have focused on this subject. We explore the possibility that the quantum vacuum energy density contributes to the (local) gravitational energy density in the framework of a scale-dependent cosmological constant Λ and Newton's constant G. This hypothesis has several important consequences, ranging from quantum scale-dependence to the hypothetical prospect of novel experimental insight concerning the quantum origin of cosmological energy density. [ABSTRACT FROM AUTHOR]

Core-collapse supernovae (SNe) are one of the most powerful cosmic sources of neutrinos, with energies of several MeV. The emission of neutrinos and antineutrinos of all flavors carries away the gravitational binding energy of the compact remnant and drives its evolution from the hot initial to the cold final states. Detecting these neutrinos from Earth and analyzing the emitted signals present a unique opportunity to explore the neutrino mass ordering problem. This research outlines the detection of neutrinos from SNe and their relevance in understanding the neutrino mass ordering. The focus is on developing a model-independent analysis strategy, achieved by comparing distinct detection channels in large underground detectors. The objective is to identify potential indicators of mass ordering within the neutrino sector. Additionally, a thorough statistical analysis is performed on the anticipated neutrino signals for both mass orderings. Despite uncertainties in supernova explosion parameters, an exploration of the parameter space reveals an extensive array of models with significant sensitivity to differentiate between mass orderings. The assessment of various observables and their combinations underscores the potential of forthcoming supernova observations in addressing the neutrino mass ordering problem. [ABSTRACT FROM AUTHOR]

Current observational data indicate that dark energy (DE) is a cosmological constant without considering its conclusiveness evidence. Considering the dynamic nature of Λ individually as a function of time and the scale factor, we review their effects on the gravitational waves. This article is a continuation of the previous work (Khodagholizadeh in JHEAp 36:48–54, 2022), in which DE only was based on Hubble's parameter and/or its derivatives. For the DE model based on the scale factor ( a - m ), the results showed that the parameter m is more limited as 2 < m ⩽ 3 compared with the other models and due to the small value of DE density at the early universe. It is only in the mode m = 3 that DE affects the low-frequency gravitational waves when its frequency is less than the 10 - 3 Hz in a matter-dominated epoch. The broad bound on reducing the amplitude and the B-B polarization multipole coefficients, from maximum to minimum, is for the models developed based on the Hubble parameter function. There are primary sources of low- and very low-frequency GWs, such as the coalescence of massive black hole binaries with M bh > 10 3 M sun , to determine the type of DE by mHz frequency space experiments (e.g., LISA) and by nHz-range NANOGrav 15-year data. [ABSTRACT FROM AUTHOR]

The majority of baryons, which account for 15% of the matter in the Universe, will end their lives as carbon and oxygen inside cold black dwarfs. Dark matter (DM) makes up the remaining 85% of the matter in the Universe; however, the fate of DM is unknown. Here we show that the destiny of purely gravitationally interacting DM particles follows one of two possible routes. The first possible route, the "radiation-destiny" scenario, is that massive DM particles lose sufficient energy through gravitational radiation, causing them to spiral into a supermassive black hole that ultimately disappears through Hawking radiation. The second possible route, the "drifting-alone" destiny, applies to lighter DM particles, where only the central DM halo region spirals into the central BH, which is then Hawking radiated away. The rest of the DM halo is ripped apart by the accelerated expansion of the Universe. [ABSTRACT FROM AUTHOR]

The thermodynamics of local causal horizons has been shown to imply gravitational dynamics. In this essay, we discuss the principles underlying this observation, and its significance in our understanding of (quantum) gravity. We also show why the local thermodynamic methods cannot by themselves recover general relativity. Instead, they lead to the so-called Weyl transverse gravity. Because of this, local thermodynamic approaches avoid huge vacuum energy contributions to the cosmological constant. They even suggest a possible source for its small observed value. We also outline a way in which thermodynamics allows us to study low energy quantum gravitational effects. We arrive at quantum corrections to the gravitational equations which are suppressed by the Planck length squared. [ABSTRACT FROM AUTHOR]

A new formula for the angular velocity of equilibrium figures of a self-gravitating rotating fluid mass is derived. An important feature of this formula is that the angular velocity is expressed in terms of the components of the inner and outer gravitational energy of the figure introduced by us earlier. We proved the adequacy of the new formula by establishing that it gives correct values of angular velocity in important special cases for sequences of homogeneous classical Maclaurin spheroids and Jacobi triaxial ellipsoids. The advantage of the new formula is that it can describe not only uniform ellipsoid equilibrium figures, but also equilibrium figures of any other geometric form, including toroidal and non-ellipsoidal configurations. This formula extends the application of the theory of equilibrium figures and provides additional possibilities for studying the equilibrium and stability of complex dynamical systems. [ABSTRACT FROM AUTHOR]

This article explores the energy behavior of two inverted, oppositely moving wave pulses as they approach each other and destructively interfere. The article presents a graphical approach to studying the energy of these wave pulses and analyzes the kinetic and potential energy associated with the pulses. The results show that the energy travels with the pulses at the same speed and that during total superposition, the only energy present is kinetic. The article provides visual representations and numerical values to support the findings. The authors acknowledge Dr. Angel Franco García for his contributions to the discussion and verification of the results. [Extracted from the article]

With the planning of new ambitious gravitational wave observatories, fully controlled laboratory experiments on dynamic gravitation become more and more important. Such experiments can provide new insights in potential dynamic effects such as gravitational shielding or energy flow and might contribute to bringing light into the mystery still surrounding gravity. Here we present a laboratory-based transmitter-detector experiment using two rotating bars as transmitter and a 42 Hz, high-Q bending beam resonator as detector. Using a precise phase control to synchronize the rotating bars, a dynamic gravitational field emerges that excites the bending motion with amplitudes up to 100 nm/s or 370 pm, which is a factor of 500 above the thermal noise. The two-bar design enables the investigation of different transmitter configurations. The detector movement is measured optically, using three commercial interferometers. Acoustical, mechanical, and electrical isolation, a temperature-stable environment, and lock-in detection are central elements of the setup. The moving load response of the detector is numerically calculated based on Newton's law of gravitation via discrete volume integration, showing excellent agreement between measurement and theory both in amplitude and phase. The near field gravitational energy transfer is 1025 times larger than the one of the propagating gravitational wave component. The ever-expanding field of gravitational wave science calls for controlled laboratory experiments on dynamic gravitation to provide insights and more precise measurements of gravity. The authors propose, model, and experimentally realize a system using two rotating bars as transmitter and a bending beam resonator as detector, finding that the near field gravitational energy transfer that creates detector amplitudes of up to 100 nm/s is 10 to the power of 25 times higher than what would be expected from gravitational waves emitted from an equivalent quadrupole gravitational wave generator. [ABSTRACT FROM AUTHOR]

A wavelike scalar-Einstein solution is found and indicating vectors constructed from the Bel-Robinson tensor are used to study which objects co-move with the wave and whether gravitational energy transfer is null. It is found that this Bel-Robinson energy criteria gives null energy transfer for both the vacuum plane wave and the scalar plane wave. [ABSTRACT FROM AUTHOR]

We consider a hybrid bimetric model where, in addition to the ordinary metric tensor that determines geometry, an informational metric is introduced to describe the reference frame of an observer. We note that the local information metric being Minkowskian explains one of the key aspects of the Einstein equivalence principle. Our approach has the potential to justify the three-dimensional nature of physical space and address the gravitational energy puzzle. Furthermore, it appears to be free of ghost instabilities in the matter sector, as the second metric tensor couples exclusively to the observer and is non-dynamical. [ABSTRACT FROM AUTHOR]

In General Relativity, the issue of defining the gravitational energy contained in a given spatial region is still unresolved, except for particular cases of localized objects where the asymptotic flatness holds for a given spacetime. In principle, a theory of gravity is not self-consistent, if the whole energy content is not uniquely defined in a specific volume. Here, we generalize the Einstein gravitational energy–momentum pseudotensor to non-local theories of gravity where analytic functions of the non-local integral operator □ − 1 are taken into account. We apply the Noether theorem to a gravitational Lagrangian, supposed invariant under the one-parameter group of diffeomorphisms, that is, the infinitesimal rigid translations. The invariance of non-local gravitational action under global translations leads to a locally conserved Noether current, and thus, to the definition of a gravitational energy–momentum pseudotensor, which is an affine object transforming like a tensor under affine transformations. Furthermore, the energy–momentum complex remains locally conserved, thanks to the non-local contracted Bianchi identities. The continuity equations for the gravitational pseudotensor and the energy–momentum complex, taking into account both gravitational and matter components, can be derived. Finally, the weak field limit of pseudotensor is performed to lowest order in metric perturbation in view of astrophysical applications. [ABSTRACT FROM AUTHOR]

In the present study we broadly explored the perception of physical and animated motion in bouncing-like scenarios through four experiments. In the first experiment, participants were asked to categorize bouncing-like displays as physical bounce, animated motion, or other. Several parameters of the animations were manipulated, that is, the simulated coefficient of restitution, the value of simulated gravitational acceleration, the motion pattern (uniform acceleration/deceleration or constant speed) and the number of bouncing cycles. In the second experiment, a variable delay at the moment of the collision between the bouncing object and the bouncing surface was introduced. Main results show that, although observers appear to have realistic representations of physical constraints like energy conservation and gravitational acceleration/deceleration, the amount of visual information available in the scene has a strong modulation effect on the extent to which they rely on these representations. A coefficient of restitution >1 was a crucial cue to animacy in displays showing three bouncing cycles, but not in displays showing one bouncing cycle. Additionally, bouncing impressions appear to be driven by perceptual constraints that are unrelated to the physical realism of the scene, like preference for simulated gravitational attraction smaller than g and perceived temporal contiguity between the different phases of bouncing. In the third experiment, the visible opaque bouncing surface was removed from the scene, and the results showed that this did not have any substantial effect on the resulting impressions of physical bounce or animated motion, suggesting that the visual system can fill-in the scene with the missing element. The fourth experiment explored visual impressions of causality in bouncing scenarios. At odds with claims of current causal perception theories, results indicate that a passive object can be perceived as the direct cause of the motion behavior of an active object. [ABSTRACT FROM AUTHOR]

For several years, research work has been carried out on energy storage that uses changes in the potential energy of masses being lifted or lowered. The energy of such a solution depends on the mass to be transported and the height to which the weight has to be lifted. Increasing the weight to be lifted is limited by the parameters of the mechanical components, such as ropes. Increasing the height, however, is difficult to implement, if only because of the weather conditions that affect the safe operation of such a system. In fact, the ideal solution is to use mine shafts, which in Poland are up to 1300 m deep. The progressive process of decommissioning the mining industry creates new opportunities to use this part of the infrastructure of mining plants for the construction of energy storage facilities. In the article, possible constructions of gravitational energy storage facilities based on existing hoisting machines are described. There are three main areas in which the operation of an energy store should be analysed if it were to be realised in a mine shaft. The mine shaft, as a working mine and for energy storage, is subject to relevant regulations that need to be met. To confirm the assumptions about the possible use of the existing infrastructure, measurements of one hoisting machine in Poland were carried out and example results of these measurements are included. [ABSTRACT FROM AUTHOR]

We discuss a cosmological scenario with a stochastic background of gravitational waves sourced by the tensor perturbation due to a hybrid inflationary model with cubic potential. The tensor-to-scalar ratio for the present hybrid inflationary model is obtained as r ≈ 0. 0 0 0 6. Gravitational wave spectrum of this stochastic background, for large-scale CMB modes, 1 0 − 4 M pc − 1 to 1 M pc − 1 is studied. The present-day energy spectrum of gravitational waves Ω 0 g w (f) is sensitively related to the tensor power spectrum and r which is, in turn, dependent on the unknown physics of the early cosmos. This uncertainty is characterized by two parameters: n ̂ t (f) logarithmic average over the primordial tensor spectral index and ŵ (f) logarithmic average over the effective equation-of-state parameter. Thus, exact constraints in the n ̂ t (f) - ŵ (f) plane can be obtained by comparing theoretical constraints of our model on r and Ω 0 g w (f). We obtain a limit on ŵ (1 0 − 1 5 Hz) < 0. 3 3 around the modes probed by CMB scales. [ABSTRACT FROM AUTHOR]

We illustrate that regular black holes and horizonless stars, typically considered as quite distinct families of black hole mimickers, are intimately intertwined. We show that any spherically symmetric regular black hole can be continuously deformed into a horizonless star under the mild conditions of non-negativity of gravitational energy (Misner-Sharp quasi-local mass), and an assumed linear relation between the latter and the Arnowitt-Deser-Misner (ADM) mass. We illustrate this general result by considering the family of geometries proposed by Hayward as the description of regular black holes, and we also describe the properties of the corresponding horizonless stars. The form of the associated effective stress-energy tensor shows that these horizonless stars can be identified as anisotropic gravastars with a soft surface and inner/outer light rings. We also construct dynamical geometries that could describe the evolution of regular black holes towards horizonless stars, and show that it is plausible that the effective stress-energy tensor in the first stages of evolution is generated by semiclassical effects, in agreement with independent works analyzing semiclassical backreaction. [ABSTRACT FROM AUTHOR]

Translation of and Commentary on Léon Rosenfeld's "Über die Gravitationwirkungen des Lichtes", Zeitschrift für Physik 65: 589–599 (1930). Originally published in German. Submitted for publication on September 26, 1930. See [1] the Comments with Referencessection before reading this English translation. The gravitational field generated by an electromagnetic field is calculated using of laws of quantum mechanics, and it is shown that the resulting gravitational energy turns out to be infinitely large, raising a new difficulty for the Heisenberg–Pauli quantum theory of wave fields. In addition, the transition processes in first-order approximation involving light and gravitational quanta [2] are briefly discussed. [ABSTRACT FROM AUTHOR]

In this paper a modeling method is validated at multiple scales for the seismic performance of multiblock tower structure (MTS). MTS are a proposed concept for large‐capacity gravitational energy storage that will enable renewable energy sources. The structure modeled is a tower of 7144 nominally identical blocks arranged in a 38‐layered annular pattern with no adhesive mechanisms between the blocks or the blocks and the foundation. The level set discrete element method is used to model the dynamics of the tower structure experiencing a ground motion. Experimental determination of each model parameter is shown from the use of individual blocks before construction. Close comparisons to experimental results are shown for the dynamic motion of the tower over a full ground motion time history for multiple scales, materials and ground motions. When the tower was brought to failure, the two ground motions used produced distinct failure modes of the tower showing both a peeling and buckling behavior. Both the effect of the friction coefficient and unequal block heights are investigated. Friction coefficient has a noticeable effect on the amplitude of motion of the tower while the unevenness of the block heights affects mostly the structural speed. [ABSTRACT FROM AUTHOR]

Gallium-based liquid metal has gained significant attention in conformal flexible electronics due to its high electrical conductivity, intrinsic deformability, and biocompatibility. However, the fabrication of large-area and highly uniform conformal liquid metal films remains challenging. Interfacial self-assembly has emerged as a promising method, but traditional approaches face difficulties in assembling liquid metal particles. Here, we realized the multi-size universal self-assembly (MUS) for liquid metal particles with various diameters (<500 μm). By implementing a z-axis undisturbed interfacial material releasing strategy, the interference of gravitational energy on the stability of floating particles is avoided, enabling the fabrication of ultra-conformable monolayer films with large areas (>100 cm2) and high floating yield (50–90%). Moreover, the films can be conformally transferred onto complex surfaces such as human skin, allowing for the fabrication of substrate-free flexible devices. This eliminates interference from traditional substrate mechanical responses, making the liquid metal e-tattoo more user-friendly. [ABSTRACT FROM AUTHOR]

We build a self-consistent relativistic scalar theory of gravitation on a flat Minkowski spacetime from a general field Lagrangian. It is shown that, for parameters that satisfy the equivalence principle, this theory predicts the same outcome as general relativity (GR) for every classical solar-system test. This theory also admits gravitational waves that propagate at the speed of light, and the gravitational radiation energy loss in a binary system is shown to be very similar to the GR prediction. We then analyze the strong gravity regime of the theory for a spherically symmetric configuration and find that there is an effective 'singularity' near the Schwarzschild radius. The main goal of this work is to show that, contrary to what is commonly believed, there are relativistic scalar theories of gravitation defined on a Minkowski spacetime that are not ruled out by the classical solar system tests of GR. [ABSTRACT FROM AUTHOR]