General Relativity and Gravitation最新文献

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.

We consider self-gravitating stationary configurations of a charged massive complex Proca field, also known as “charged Proca stars", in the particular case of spherical symmetry. We first present a general 3+1 decomposition of the Einstein–Maxwell–Proca system, starting from the action and field equations. We then restrict our system to the case of spherical symmetry and, after imposing a harmonic time dependence ansatz for the Proca field, we construct families of charged Proca stars for different values of the charge parameter q, and different values of the central Proca scalar potential (varphi ). In a similar way to the case of scalar boson stars, one can define a critical charge (q=q_c) that corresponds to the value for which the Coulomb repulsion of the charged Proca field exactly cancels their newtonian gravitational attraction. Just as in the case of boson stars studied in [1, 2], we find that supercritical solutions can exist for a limited range of charges above the critical value (q>q_c). We also consider the binding energy (E_B) for the different families of solutions, and find that gravitationally bound solutions such that (E_B<0) can only exist for subcritical charges such that (q<q_c), indicating that our supercritical solutions are probably dynamically unstable against perturbations.

In this study, we examine thermodynamic parameters along with the BH evaporation. For this purpose, we chose BHs with global monopoles because the existence of global monopoles near a BH may influence the rate at which it loses mass and ultimately evaporates. We also analyze the thermodynamic parameters, local and global stability in the presence of entropy with exponential correction term. Furthermore, we consider the thermodynamic geometry with respect to entropy, charge, and thermodynamic pressure. In addition, we discover that the zero point of heat capacity aligns with the Ricci scalar which is obtained from the Ruppeiner metric, indicating the phase transition. However, our most exciting finding in this study is that BH evaporation is rapid for stable BHs but slow for unstable BHs. Interestingly, raising the values of global monopole can accelerate the evaporation process.

Considering an exact solution of the five-dimensional vacuum Einstein equations, which represents a distorted Myers-Perry black hole with a single angular momentum, we investigate how the distortion affects the horizon surface of this black hole. We illustrate a special case where a bumpy deformed black hole horizon feels the presence of the external sources. However, the ergosphere is oblivious to the presence of external sources.

We present an analysis of phantom energy dominated conformal cyclic baby universes evolving inside black holes. For stable black holes, the analysis yields an infinite sequence of conformal cycles. This sequence terminates at a critical number (n_{text {crit}} approx epsilon ^{-1}ln (2M_0/ell _{text {Pl}})). At this point, the interior approaches a Planck-scale remnant in finite proper time. For evaporating BHs, the discussed solutions indicate that a phantom-dominated interior branch can outgrow the shrinking horizon if (b_0 > 2M_0(tau _s - v_0)^{-mu /3}). These timescales are shorter than Hawking evaporation. The model exhibits a possible semiclassical avoidance of the Schwarzschild singularity via effective LQG dynamics. A phantom-dominated branch extends the interior evolution beyond the bounce. The conformal mapping suggests, at a heuristic level, a possible channel for information leakage. We discuss possible observational signatures, such as gravitational-wave echoes and CMB circular anomalies. We also discuss a complex-time formulation that captures the accumulation of cycles.

By implementing a full non-linear treatment of f(R) gravity in static and spherically symmetric spacetimes, we analyze two scenarios. The first one within the context of the solar-system tests where we try to recover the chameleon effects without any approximations in the equations (e.g. linearization) from f(R) models that are compatible with cosmology. The second scenario deals with a quadratic f(R) model that is tested in neutron stars. This scenario, which is associated with strong gravity, is completely independent from the first one, but exploits the fact that the equations and formalism are basically the same in both applications. The difference between the two goals lies mainly in the values of the constants involved in the specific f(R) models and the equation of state (EOS) of the central object (Sun or neutron star), but the numerical techniques and the general form of the field equations remain valid in both situations. For the neutron star problem we employ for the first time and in the context of f(R) gravity a multiple algebraic polytropic EOS that mimics accurately realistic EOS in several density ranges. By doing so we avoid the numerical interpolation needed when a realistic EOS is given in tabulated form. Furthermore, we compare our results with the latest data, which includes the most massive neutron star known to date of about (2.35 M_odot ) from PSRJ0952-0607.

The intricacy of the gravitational field poses a central challenge for quantum gravity, since a full nonperturbative quantization of the spacetime metric remains analytically intractable. The Kantowski-Sachs minisuperspace model, widely used for the black hole interior, offers a useful simplification but may overly constrain the quantum dynamics near the classical singularity. We therefore propose in this paper an enlarged minisuperspace model that extends the Kantowski-Sachs framework by incorporating an additional metric degree of freedom. This minimal extension enriches the dynamical structure of the model and allows for a more nuanced exploration of the quantum geometry in the black hole interior while maintaining analytical tractability. Applying canonical quantization to this enlarged minisuperspace, we obtain the corresponding Wheeler-DeWitt equation. Remarkably, we find that this model is amenable to exact analytical solution, yielding the wave function of the black hole interior. The resulting wave function (Psi ) is regular across the entire interior region of the black hole and it approaches zero in the region where the classical singularity would occur. Thus the wave function complies with the DeWitt criterion for singularity resolution, (Psi rightarrow 0), upon approaching the classical singularity. This limit implies that the probability of the geometry attaining the singular configuration is zero in quantum gravity. Physically, this outcome suggests that the classical singularity is replaced by a quantum region where the geometry remains regular. The exact solvability of the enlarged minisuperspace model thus offers a valuable analytical implementation in providing higher assurance and greater confidence in quantum resolution of the black hole singularity.