General Relativity and Gravitation最新文献

We present the first fully explicit, continuous, analytically derived warp–drive spacetime within General Relativity whose shift–vector flow is kinematically irrotational. Building on Santiago et al. that scalar–potential, zero–vorticity warp fields are Hawking–Ellis Type I for unit lapse and flat spatial slices, we supply a closed–form scalar potential and smooth shift components with proper boundary behavior, together with a Cartan–tetrad analytic pipeline and high–precision eigenanalysis. Compared with the Alcubierre and Natário models (evaluated at identical ((rho ,sigma ,v/c))), our irrotational solution exhibits significantly reduced local NEC/WEC stress: its peak proper–energy deficit is reduced by a factor of (approx 38) relative to Alcubierre and (approx 2.6times 10^{3}) relative to Natário, and its peak NEC violation is more than (60times ) smaller than Natário. Crucially, the stress–energy is globally Hawking–Ellis Type I, with a well–defined timelike eigenvalue (proper energy density) everywhere. A fixed–smoothing vortical ablation confirms that this improvement is causally due to irrotational, curl–free kinematics rather than profile shaping: adding modest vorticity collapses the (E_{+}/E_{-}) balance and drives large increases in the negative–energy magnitude (E_{-}). We quantify the negative–energy requirement via a slice-integrated (on (Sigma _t)) negative–energy volume and tabulate global measures. A far–field extrapolation to (R!rightarrow !infty ) yields tail–corrected totals (|E_+-E_-|/(E_++E_-)=0.04%). Thus the net proper energy is consistent with zero to four decimal places (in fractional units). We also establish regularity at (r=0) for the irrotational construction.

Black bounces are compact objects with a wormhole structure hidden behind an event horizon. This type of metric can be obtained through general relativity by considering the presence of exotic matter. Such spacetimes can also arise within the framework of effective theories inspired by loop quantum gravity. In this work, we verify the possibility of obtaining black bounce models inspired by loop quantum gravity as solutions of general relativity. For this, we examine which sources can generate these solutions and the consequences of using these types of sources. We find that the sources can be expressed as a combination of a phantom scalar field and nonlinear electrodynamics. Once we obtain the sources in terms of fields, we analyze the energy conditions for each field separately to verify which of the fields is responsible for the violation of the energy conditions.

We study the cosmological dynamics of non-minimally coupled matter models using Brown’s variational approach to relativistic fluids in General Relativity. After decomposing the Ricci scalar into a bulk and a boundary term, we construct new models by coupling the bulk term to the fluid variables and an external scalar field. Using dynamical systems techniques, we study models of this type and find that they can give rise to both early-time inflationary behaviour and late-time accelerated expansion. Moreover, these models also contain very interesting features that are rarely seen in this context. For example, we find dark energy models which exhibit phantom crossing in the recent past. Other possibilities include models that give a viable past evolution but terminate in a matter-dominated universe. The dynamical systems themselves display an array of mathematically interesting phenomena, including spirals, centres, and non-trivial bifurcations depending on the chosen parameter values.

We extend well-known results on the Newtonian limit of Lorentzian metrics to orthonormal frames. Concretely, we prove that, given a one-parameter family of Lorentzian metrics that in the Newtonian limit converges to a Galilei structure, any family of orthonormal frames for these metrics converges pointwise to a Galilei frame, assuming that the two obvious necessary conditions are satisfied: the spatial frame must not rotate indefinitely as the limit is approached, and the frame’s boost velocity with respect to some fixed reference observer needs to converge.

This investigation highlights an important application of complete geometric decoupling in constructing anisotropic, compact density-matter stars via a decoupled gravitational framework. In this context, the present study introduces an intriguing synthesis of two independent techniques, density-like constraints and the zero-complexity factor, to simultaneously derive the decoupler functions. By using this innovative relativistic scheme, we gain the ability to analytically control the anisotropies and complexity when modeling the dense-matter compact stars. We show that the complexity-free condition effectively captures the influence of anisotropic pressure inherent in compact dense-matter distributions, arising naturally from the chosen seed metric ansatz. Two distinct and physically viable anisotropic models satisfying all standard stability and energy conditions are obtained through the complete decoupling process. Our findings provide clear theoretical understanding of the coupling between known and standard gravity fields by demonstrating for the first time that the parameter responsible for deformation uniquely governs the direction of energy transfer between the seed sector and the decoupling source.

We investigate the cosmic inflation within a class of the scalar-tensor model with the scalar-dependent non-minimal kinetic couplings. The inflationary dynamical potential will be applied. Using the slow-roll approximation, we compute theoretical predictions for the key observables, like the spectral indexes (n_s), scalar-to-tensor ratio r and the running of the scalar spectral index (alpha _s) in terms of the free parameters of the model. Besides, we find the limitations of these parameters. In addition, these quantities will be compared with the latest observational data from the Planck data. Furthermore, we analyze the sensitivity of r, (n_s) and (alpha _s) in terms of the model’s free parameters.

Non-conservation of dark matter can lead to late-time cosmic acceleration. This mechanism is known as the matter creation theory and this replaces the need of dark energy and modified gravity theories. We consider a two-fluid system consisting of a cold dark matter and a second fluid with constant barotropic equation of state. We performed detailed investigations of such cosmologies using the powerful techniques of qualitative analysis of dynamical systems. Considering a wide variety of the creation rates, we examine the phase space analysis of the individual scenario. According to our analyses, these scenarios predict decelerating unstable dark matter (or second fluid) dominated critical points, accelerating attractors dominated either by dark matter or the second fluid, accelerating scaling attractors in which dark matter and the second fluid co-exist. The regime of late-time accelerating expansion can be classified as either quintessence, phantom or driven by a cosmological constant. This huge variety of critical points makes these scenarios phenomenologically rich, and naturally suggests that such scenarios can be viewed as viable and potential alternatives to the mainstream cosmological models.

We present a new methodology to explore the morphology of the High Frequency Feature (HFF), i.e., the dominant, rising-frequency GW emission from a proto-neutron star in core-collapse supernovae (CCSNe). We used a residual neural network (ResNet50) to perform multi-class classification of image samples constructed from time–frequency Morlet wavelet scalograms. We defined a three-class problem by categorizing the HFF slope as Steep, Moderate, or Low, according to physically informed ranges. The ResNet50 model was optimized with phenomenological waveforms injected into real noise from the LIGO-Virgo O3b observing run and then tested with numerically simulated CCSN waveforms embedded in the same real noise. At galactic distances of 1 kpc and 5 kpc with H1 and L1 data and 1 kpc with V1 data, we obtained highly accurate results (test accuracies from 0.8933 to 0.9867), which show the feasibility of our methodology. For further distances, we observed declines in test accuracy until 0.8000 with H1 and L1 data at 10 kpc and until 0.5933 with V1 data at 10 kpc, which we attribute to limitations in the input datasets. Our methodology is sufficiently general to enable early-stage characterization of the HFF in real interferometric data.

In our previous work [H. Zejli, Int. J. Mod. Phys. D 34, 2550052 (2025), arXiv:2508.00035], we introduced a (mathcal {P}mathcal {T})-symmetric wormhole model based on a bimetric geometry, capable of generating closed timelike curves (CTCs). In this paper, we extend the analysis to the null hypersurface at the throat of this modified Einstein-Rosen bridge, where two regular Eddington-Finkelstein metrics render the geometry traversable. Using the Barrabés-Israël formalism in Poisson’s reformulation, we evaluate the null shell’s surface stress-energy tensor (S^{alpha beta }) from the jump of the transverse curvature, revealing a violation of the null energy condition: a lightlike membrane of exotic matter with negative surface energy density and positive tangential pressure. This exotic fluid acts as a repulsive source stabilizing the throat, ensuring consistency with the Einstein field equations, including conservation laws on the shell. Beyond the local characterization, we outline potential observational signatures: (i) gravitational-wave echoes from the photon-sphere cavity; (ii) horizon-scale imaging with duplicated and through-throat photon rings, and non-Kerr asymmetries; (iii) quantum effects such as (mathcal{P}mathcal{T})-induced frequency pairing with possible QNM doublets and partial suppression of vacuum flux at the throat; and (iv) a relic cosmological population yielding an effective (Lambda _textrm{eff}) and seeding voids. Compared with timelike thin-shell constructions, our approach is based on a null junction interpreted as a lightlike membrane, combined with (mathcal{P}mathcal{T}) symmetry, providing a distinct route to traversability and clarifying the conditions under which CTCs can arise in a self-consistent framework.

We consider scalar perturbations of the Reissner–Nordström family and the Kerr family. We derive a characteristic expression of the radiation field, at any given fixed angle of future null infinity, and numerically show that its amplitude gets excited only in the extremal case. Our work, therefore, identifies an observational signature for extremal black holes. Moreover, we show that the source of the excitation is the extremal horizon instability and its magnitude is exactly equal to the conserved horizon charge.