The onset of convection in a fluid-saturated anisotropic porous medium with the effect of the variable gravity field and throughflow using LTNE model

Hybrid analytical–ANN modeling of ferroconvection with couple stresses under variable gravity fields

Abstract We investigate the possibility of obtaining traversable wormholes supported by real phantom scalar fields in Lorentz-violating gravity with an antisymmetric rank-2 tensor with a non-zero vacuum expectation value non-minimally coupled to the curvature tensor. This Lorentz violation framework shows to be a suitable scenario to search for wormhole solutions in the presence of Lorentz violation since it introduces mild constraints on the areal radius. The vacuum expectation value of the antisymmetric rank-2 tensor, nonetheless, imposes constraints on the lapse function. As a consequence, under the vacuum configuration adopted, the allowed lapse functions can be either constant, linear, or quadratic, depending on the self-interaction potential that drives the spontaneous breaking of the Lorentz symmetry. Thus, we find the Ellis–Bronnikov counterpart in this Lorentz-violating scenario as well as Lorentz-violating wormholes with a Rindler-type acceleration and an effective cosmological constant. Properties of these wormholes, such as their non-flat asymptotics, are investigated.

Abstract We revisit the balance equations for energy and momentum in general spacetimes. Specifically, we consider the action of gravity and matter fields as a theory in Minkowski spacetime, which is deformed through arbitrary given metric functions $g_{\mu\nu}(x)$. This differs from the standard approach, where the metric is considered as a dynamical field, in that the given metric coefficients introduce an explicit coordinate dependence into the theory which generically breaks all translational invariances. The advantage of our method is that it shows explicitly how the given spacetime metric breaks energy and momentum conservation. The results provide a complementary derivation, and a pedagogical illustration, that energy-momentum balance amounts to the covariant equation $D_\mu T^{\nu\mu}=0$, even if $T^{\nu\mu}$ refers to subdominant energy-momentum components, i.e., to matter fields which do not contribute to the Einstein equation because other matter fields dominate the evolution of spacetime.

Abstract We probe potential variations of the proton-to-electron mass ratio ( $$\mu $$ μ ) using high-resolution H $$_2$$ 2 Lyman transitions in the white dwarf GD 133, observed with the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS). White dwarf atmospheres provide a powerful laboratory for testing fundamental physics in strong gravitational fields. Applying a self-consistent spectral analysis, we obtain a tight constraint of $$\Delta \mu /\mu = (0.02 \pm 0.09)$$ Δ μ / μ = ( 0.02 ± 0.09 ) in a gravitational potential approximately $$10^{4}$$ 10 4 times stronger than that of Earth. The measured uncertainty implies that any variation of $$\mu $$ μ is tightly bounded in this strong-field fields, placing meaningful limits on models predicting couplings between fundamental constants and gravity.

Underground gas storage facilities are strategically important complex engineering facilities used for seasonal storage of natural gas resources, ensuring energy security and increasing the reliability of gas supply systems. During the injection of gas under high pressure into the deep layers of the earth's crust and its subsequent extraction for production purposes, a significant anthropogenic impact is exerted on environmental components - soil cover, groundwater and surface water horizons, atmospheric composition, as well as local biocenoses. These processes are accompanied by the risks of deformation of the earth's surface, disruption of the groundwater balance, emission of greenhouse gases and damage to ecosystems. The presented article systematically studies and classifies modern analytical methods applied for a comprehensive assessment of the ecological situation in the areas of operation of underground gas storage facilities. The research covers geophysical monitoring technologies - recording microseisms using seismoacoustic stations, measuring variations in the gravity field with high-precision gravimeters and mapping the electrical conductivity of soil layers using electromagnetic methods. Various systems allow for early detection of environmental changes, ensuring compliance of the operation of underground gas storage facilities with national and international safety standards, and proactive minimization of potential environmental risks. The article also discusses the principles of integration of various analysis methods, their synergistic mechanisms, advantages, and practical application areas in a scientifically and technically justified manner. Keywords: underground gas storage, environmental monitoring, geophysical methods, satellite data, geochemical analysis, hydrogeological parameters, environmental risk, safety, environment, mathematical modeling.

This study investigates the impact of gravitational fields on the spectroscopic structure of the Feshbach-Villars oscillator (FVO) within Gürses space-time. Utilizing the first-order Feshbach-Villars formulation of the Klein-Gordon equation, which describes relativistic wave dynamics for spinless particles, we analyze the quantum mechanical properties of the oscillator under a Coulomb-type potential. The corresponding wave functions and energy levels are derived for both free and interacting cases. Furthermore, we explore the effects of the interaction between the Coulomb-type potential and Gürses space-time on the behavior of the Feshbach-Villars oscillator, particularly in relation to its spectroscopic characteristics. This research provides valuable insights into the intricate relationship between quantum mechanics, relativity, and gravitational fields at the microscopic level.

Abstract. The Gravity Recovery And Climate Experiment (GRACE) and its follow-on mission, GRACE-FO, have observed global mass changes and transports, expressed as terrestrial water storage anomalies (TWSA), for over two decades. However, for climate model evaluation, climate change attribution and other applications, multi-decadal TWSA time series are required. This need has triggered several studies on reconstructing TWSA via regression approaches or machine learning techniques, with the help of predictor variables such as rainfall, land or sea surface temperature. Here, we combine such an approach, for the first time, with large-scale time-variable gravity information from geodetic satellite laser ranging (SLR) and Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) tracking. The new reconstruction TWSTORE (Terrestrial Water STOrage REconstruction) is formulated in a GRACE-derived empirical orthogonal functions (EOFs) basis and complemented with the Löcher et al. (2025) approach, in which global gravity fields are solved from SLR ranges and DORIS observations in EOF space for the pre-GRACE time frame. Our approach is highly modular, allowing to use different data sets at several steps in the workflow. We reconstruct GRACE-like TWSA for the global land, excluding Greenland and Antarctica, from 1984 onward. We find that the new combined reconstruction inherits information from the geodetic method, mainly at longer timescales. In contrast, at the seasonal scale, the climate-driven reconstruction and the geodetic product are already surprisingly consistent. In comparison to other reconstructions, we find thus major differences mainly at the multi-decadal timescale. All in all, our study confirms the presence of significant changes in storage trends, showing that GRACE-derived results should not be extrapolated to the past. The reconstructed fields and corresponding uncertainty information are available at https://doi.org/10.5281/zenodo.15827789 (Hacker, 2025). We also derive evaporation based on the water balance equation and the presented reconstruction for 11 river basins. The corresponding time series are available at https://doi.org/10.5281/zenodo.16643628 (Gutknecht, 2025).

We investigate whether Newtonian gravity can generate quantum entanglement between mesoscopic quantum bodies modeled as superposed mass quadrupoles using three complementary approaches: minisuperspace, semiclassical gravity, and stochastic gravity. We systematically analyze gravitationally induced entanglement (GIE) mechanisms and the conditions under which they can arise. Our results support the GIE hypothesis by showing that the minisuperspace framework, which quantizes the parity of the gravitational tidal field, can entangle spatially separate quantum bodies. In contrast, the semiclassical and stochastic gravity models, in which the tidal gravitational field sourced by the quantum bodies remains classical, fail to entangle the final state. These findings clarify recent claims that classical gravity might induce entanglement, and reveal how perturbative treatments can lead to misleading conclusions.

Forward-backward internal resonances in asymmetrical rotors under electromagnetic and gravitational fields

ABSTRACT In this study, we present a novel exact solution to the gravitational field equations, known as the Ayón‐Beato–García black hole (BH) solution, set against the backdrop of anti‐de Sitter space and surrounded by a quintessence field (QF). This solution serves as an interpolation between three distinct anti‐de Sitter BH configurations, namely, the Ayón‐Beato–García, Schwarzschild–Kiselev, and the standard Schwarzschild BH solutions. The first aspect of our investigation focuses on the geodesic motion of particles, where we explore how the BH's space‐time geometry‐incorporating the effects of nonlinear electrodynamics (NLED), the QF, and the curvature radius‐influences the dynamics of both massless and massive particles near the BH. To further enrich our analysis, we extend the study to include the perturbative dynamics of a massless scalar field within the BH solution, placing special emphasis on the scalar perturbative potential. Subsequently, we focus into the phenomenon of BH shadows, examining how various parameters, such as the NLED, the curvature of space‐time, and the presence of the QF, impact the size and shape of the shadow cast by the BH. In the final segment of our study, we shift our attention to the thermodynamics of the BH solution. We compute several essential thermodynamic quantities, including the Hawking temperature, specific heat capacity, and Gibbs free energy, analyzing how these properties evolve in response to changes in the various parameters that define the space‐time geometry, which in turn affect the gravitational field when compared to the traditional BH solutions.

Neutron stars (NS), with their extreme gravitational and magnetic fields, provide an exceptional astrophysical laboratory for studying axion dark matter (DM). Through the Primakoff effect, axions can convert into photons within the magnetospheres of NS, a process that may produce observable radio and X-ray signals. In this work, we investigate axion-photon conversion using a novel, time-dependent state evolution formalism, moving beyond the commonly used stationary-path approximations. We derive a generic analytical expression for the conversion probability and calculate the associated radiated power. Our analysis demonstrates that this approach allows NS to strongly constrain the axion-photon coupling constant, reaching sensitivities of gaγγ ≃ 10−14 −10−15 GeV−1 for axion masses of ma ≃ 10−3 −10−10 eV. These results establish a new pathway to constrain gaγ via NS observations. Future campaigns using powerful observatories like the James Webb Space Telescope (JWST), Green Bank Telescope (GBT), and More Karoo Array Telescope (MeerKAT) array will be ideally suited to probe the distinct spectral signatures predicted by our model across multiple frequency domains.

Testing strong gravitational field using the Johannsen–Psaltis metric: Bondi–Hoyle–Lyttleton accretion model and QPO studies

Abstract The ESA GOCE satellite carried a gravity gradiometer consisting of three pairs of accelerometers on mutually orthogonal axes. For each accelerometer, bias and scale factors have been re-estimated by a dynamic precise orbit determination (POD) using improved gravity field modeling and standards. The kinematic orbit solution included in GPS-based Precise Science Orbit (PSO) product served as the baseline observables for 1210 daily arcs, covering the period from 1 November 2009 to 20 October 2013. Implementing improved force models almost completely resolved the deviations of the Y -axis scale factor obtained in earlier work (Visser and Ijssel 2016). A novel aspect is the verification by comparison with dynamic POD solutions based on SLR observations using 51 two-day orbital arcs. A high level of consistency was obtained between the kinematic PSO- and SLR-based accelerometer calibration parameters, e.g. within 0.01 nm/s $$^{ 2}$$ 2 for the X -axis pointing predominantly in the flight direction in terms of bias. One set of accelerometer scale factors was estimated for the entire mission. These were found to be consistent to within 0.005 for all accelerometer axes. The three-dimensional consistency between the dynamic orbits and the PSO reduced-dynamic orbit solutions has a mean Root-Mean-Square (RMS) of 4.5 and 10 cm, respectively, for the PSO reduced-dynamic and SLR-based dynamic orbit solutions. In addition, the one-dimensional RMS-of-fit of the PSO kinematic orbit solution improved significantly from 6.9 in Visser and Ijssel (2016) to 2.6 cm.

Abstract The GRACE and GRACE Follow-On (GRACE-FO) missions aim to track temporal changes in Earth's gravity field. Using data from these missions, CNES/GRGS has produced the “RL05” satellite-only series of geopotential solutions in spherical harmonics up to degree and order 90. These solutions are available at both monthly and 10-day temporal resolutions, covering the period from April 2002 to July 2025. These solutions were derived using a distinct processing strategy—particularly with respect to background models and solution stabilization techniques—compared to those adopted by most other groups involved in GRACE/GRACE-FO data processing. Nevertheless, the core parameter estimation approach remains fundamentally the same. The main differences with other processing centers are the combination of Satellite Laser Ranging (SLR) data from geodetic satellites with GRACE data at the normal equation level (and not as a substitution of low-degree SH coefficients) and the use of truncated singular value decomposition (TSVD) for the time-variable gravity (TVG) field solution. Examination of TVG time series over test areas such as the Caspian Sea and Iceland demonstrates the advantages of TSVD resolution over conventional unconstrained methods such as Cholesky decomposition, which require post-processing filtering. The DDK5 filter, for instance, produces a strong decrease in the restored signal from spherical harmonic degree 50, compared to approximately degree 70 for the TSVD solution. Our TSVD solution is also compared to mascon solutions, showing a commensurability of the signal content of the solutions, with the advantage of not relying on geophysical assumptions and of providing, on the oceans, a less constrained solution than mascons. Finally, an evaluation of the noise of these different solutions is carried out by estimating and comparing the errors of the solutions on the regions where the TVG signal is particularly weak. The noise is estimated at the level of 1.0 to 4.6 cm equivalent water height (EWH), depending on the resolution, for the DDK5-filtered RL06 solutions from CSR, JPL and GFZ, and at the level of 0.9–3.3 cm EWH for the COST-G, TUGRAZ and CNES-RL05-TSVD solutions.

The two most severe cosmological tensions in the Hubble constant \(H_0\) and the matter clustering amplitude \(S_8\) have the same relative discrepancy of 8.3%, which suggests that they may have a common origin. Modifications of gravity and exotic dark fields with numerous free parameters introduced in the Einstein field equations often struggle to simultaneously alleviate both tensions; thus, we need to look for a common cause within the standard \(\Lambda\)CDM framework. At the same time, linear perturbation analyses of matter in the expanding \(\Lambda\)CDM universe have always neglected the impact of comoving peculiar velocities \(\mathbf{v}\) (generally thought to be a second-order effect), the same velocities that, in physical space, cannot be fully accounted for in the observed late-time universe when the cosmic distance ladder is used to determine the local value of \(H_0\). We have reworked the linear density perturbation equations in the conformal Newtonian gauge (sub-horizon limit) by introducing an additional drag force per unit mass \(-\Gamma(t)\mathbf{v}\) in the Euler equation with \(\Gamma \equiv \gamma(2 H)\), where \(\gamma\ll1\) is a positive dimensionless constant and \(2H(t)\) is the time-dependent Hubble friction. We find that a damping parameter of \(\gamma = 0.083\) is sufficient to resolve the \(S_8\) tension by suppressing the growth of structure at low redshifts, starting at \(z_\star\simeq 3.5\)–6.5 to achieve \(S_8\simeq 0.78\)–0.76, respectively. Furthermore, we argue that the physical source causing this additional friction (a tidal field generated by nonlinear structures in the late-time universe) is also responsible for a systematic error in the local determinations of \(H_0\)—the inability to subtract peculiar tidal velocities along the lines of sight when determining the Hubble flow via the cosmic distance ladder. Finally, the dual action of the tidal field on the expanding background—reducing both the matter and the dark energy sources of the squared Hubble rate \(H^2\), thereby holding back the cosmic acceleration \(\ddot a\)—is of fundamental importance in resolving cosmological tensions and can also substantially alleviate the density coincidence problem.

Abstract We investigate the relative alignment between density structures and magnetic fields in eight young protostars from the Atacama Large Millimeter/submillimeter Array B -field Orion Protostellar Survey. Column density maps are derived from 870 μ m dust continuum emission, and the Histogram of Relative Orientations method is applied to quantify the correlation between magnetic field orientations and density structures on envelope scales (∼10 3 au). We find that the relative alignment shows overall little evidence of systematic evolution with column density, suggesting that column density alone does not fully determine the alignment. The magnetization level also plays a crucial role, with weakly magnetized envelopes exhibiting predominantly parallel or random alignment, whereas strongly magnetized ones show perpendicular configurations even at moderate densities. These results reveal that density and magnetization jointly shape the morphology of protostellar envelopes and the coupling between gravity and magnetic fields during early stages of star formation.

This study investigates the interconnection between Weyl's curvature tensor \(W_{jkh}^i\) and Cartan's second curvature tensor \(P_{jkh}^i\) in the frame of Finsler geometry (or \(F\)-geometry), a broader framework that generalizes Riemannian geometry(or \(R\)-geometry). When describing the curvature characteristics of \(F\)-space which are crucial for simulating a variety of physical events both tensors are crucial. Even though the geometric meanings and physical consequences of these tensors have been thoroughly investigated, their interconnection remains an open area for research. In the present work, we demonstrate that the Weyl's and Cartan's second curvature tensors are connected by a novel set of identities and inequalities that we deduce by examining their algebraic and geometric characteristics. A series of theorems that outline particular circumstances in which the tensors exhibit generalized birecurrent behavior in Finsler spaces (or \(F\)-spaces) are presented. In addition to offering further insight into how these notions are applied in physics, especially in the gravitational field and cosmology, these results are anticipated to improve our knowledge of the curvature structure in \(F\)-spaces and yield interesting findings in the frame of differential geometry and its physical applications.

Modeling the temporal gaps between GRACE and GRACE-FO data in Iran using MLP neural network

The dynamic approach integrates Global Positioning System and K-band range-rate (KRR) observations to enable precise orbit determination (POD) and gravity field recovery. However, background model uncertainties and temporal aliasing introduce frequency-dependent noise into the post-fit KRR residuals, thereby degrading overall solution accuracy. To mitigate these effects, empirical signals are typically modeled using either dynamic (DYN) or kinematic (KIN) parameterization strategies. Nevertheless, the combined use of DYN and KIN parameterizations remains largely unassessed, and their potential synergistic impact on POD and gravity field recovery merits systematic evaluation. This study evaluates the individual and joint impacts of DYN and KIN (DYN+KIN) on The Gravity Recovery and Climate Experiment (GRACE) Follow-On orbit accuracy and monthly gravity field recovery using nearly one year of 2019 data (excluding February due to severe data gaps). The refined solutions act as empirical temporal filters, effectively suppressing low-frequency components in KRR residuals, particularly below 1-cycle-per-revolution. Relative to nominal ambiguity-fixed reduced-dynamic orbits, the refined solutions mainly enhance the cross-track component, with DYN+KIN showing the largest improvement, while along-track precision experiences only minor (sub-millimeter) degradation. Overall three-dimensional orbit accuracy improves from 3.8 cm to 3.0 cm (DYN), 2.8 cm (KIN), and 2.8 cm (DYN+KIN). In terms of gravity field recovery, the DYN+KIN solution begins to exhibit more pronounced deviations from the other solutions beyond degree and order 30. Over oceanic regions, residual mass anomaly analysis shows that the DYN+KIN solution is associated with an approximately 16% higher noise level compared to the individual DYN and KIN strategies, which exhibit modest noise reductions relative to the nominal solution. The DYN+KIN also exhibits a dampened ~160-day periodicity in the temporal evolution of low-degree coefficients (e.g., C2,0), likely due to spectral overlap between empirical parameter frequencies and low-degree gravity signal components. These results indicate that over-parameterization introduces spectral redundancy and absorbs geophysical signals, underscoring the need to balance parameter flexibility and signal fidelity in gravity recovery strategies.