General Relativity and Gravitation最新文献

In this study, we analyzed the polarization modes of gravitational waves in an anisotropic Bianchi type I theory. We present the model and construction of gravitational waves, and discuss the gauge problem that appears specifically in these calculations. As the theory allows up to two independent polarization modes, we analyzed the various cases that arise, depending on the wave vector (textbf{k}), and presented the differences and similarities as the homogeneous and isotropic model, described by the Friedmann-Lemaître-Robertson-Walker metric. Once the general structure of the model has been established, the analysis of the polarizations of gravitational waves in a specific theory is carried out, using as a model the Kasner scenario, which can be considered Bianchi type I model in the absence of matter and cosmological constant.

A Newtonian-like theory inspired by the Brans-Dicke gravitational Lagrangian has been recently proposed in Ref. [1]. We propose here a new variant of this theory such that the usual Newtonian second law is preserved. The cosmological solutions are analysed and accelerated background expansion can be obtained even in a pure matter dominated universe. This happens due to the dynamic character of the effective gravitational coupling which is sourced by a time evolving scalar field . We also analyse the matter density perturbations and find they exhibit an enhanced growth in comparison with the usual Newtonian like behavior in Einstein-de Sitter model.

We investigate the gravitational lensing signatures of vorton configurations, considering the circular vorton, the Kibble–Turok vorton, and a newly proposed class that incorporates simultaneous excitations of the first, second, and third harmonic modes. Working within the weak-field and thin-lens approximations, we demonstrate that circular vortons produce a sharp lensing discontinuity that separates two regions with qualitatively distinct distortions. The corresponding Einstein ring co-exists alongside an almost undistorted source image. This effect is significantly amplified in the case of non-circular vortons, where asymmetries and higher-harmonic deformations amplify the discontinuity and lead to complex image structures. These distinctive lensing patterns offer potential discriminants between different vorton configurations, suggesting that future high-resolution surveys may provide a novel window into the microphysics of current-carrying cosmic strings.

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.