International Journal of Modern Physics D

The performance of quantum information protocols can be impacted by the noninertial motion of parties such as in a gravitational field. Previous studies have primarily focused on the degradation of entanglement for global modes, revealing that bipartite entanglement vanishes in the limit of large acceleration, whereas tripartite entanglement does not. In this study, we examine the impact of acceleration on tripartite Gaussian resource states encoded in spatially localized wave packets. Contrarily to prior findings, we observe that genuine tripartite entanglement (GTE) vanishes in the limit of large acceleration for various initial states and observer trajectories.

The aim of this paper is to obtain new physically admissible exact anisotropic stellar models via gravitational decoupling technique. This will be done by taking Korkina and Orlyanskii model solution as a seed solution and extend it to an anisotropic domain via gravitational decoupling through the minimal geometric deformation (MGD) approach. We analyze the physical properties of four compact star models Her $X-1$ (Mass $M=0.85M_{\mathrm{\Theta }}$, $\mathrm{\text{radius}}=8.1$km), LMC $X-4$ ($M=1.04M_{\mathrm{\Theta }}$, $\mathrm{\text{radius}}=8.301$km), PSR $\mathrm{\text{J}}1903+327$ ($M=1.667M_{\mathrm{\Theta }}$, $\mathrm{\text{radius}}=9.438$km) and PSR $\mathrm{\text{J}}1614-2230$ ($M=1.97M_{\mathrm{\Theta }}$, $\mathrm{\text{radius}}=9.69$km). We demonstrate the stability conditions of the obtained solution by plotting energy conditions, velocity of sound, adiabatic index and all the thermodynamic parameters and equilibrium conditions via TOV equation, etc. We found that the results are physically well behaved and also fulfill the requirement of stability criteria inside the anisotropic fluid sphere. We study the physical features of the solutions in detail, analytically and graphically for the four compact stars Her $X-1$, LMC $X-4$, PSR $\mathrm{\text{J}}1903+327$ and PSR $\mathrm{\text{J}}1614-2230$. Based on the results we realized that the extended gravitational decoupling technique is very effective for the analysis of the interior of the compact stellar structures.

In the light of Dirac’s Large Number Hypothesis (LNH), we try to relate the Drake equation with the extra-terrestrial intelligence (ETI), specifically in terms of cognitive science. This argument has been drawn from the ratio of smallest time scale (i.e. 40Hz oscillation in neuronal system of brain) to the smallest timescale (i.e. the Planck time in the present universe) which provides a very large dimensionless number $10^{40}$. Under this LNH, we emphasize on the issue of the alien equation of Drake and provide a modified version of it by considering consciousness of the ETI. Thus, the Drake equation, which basically represents a statistical conjecture with random and arbitrary values, can be related with a feasible as well as applicable background philosophy.

Second-order-derivative plus fourth-order-derivative gravity is the ultraviolet completion of second-order-derivative quantum Einstein gravity. While it achieves renormalizability through states of negative Dirac norm, the unitarity violation that this would entail can be postponed to Planck energies. As we show in this paper, the theory has a different problem, one that occurs at all energy scales, namely that the Dirac norm of the vacuum of the theory is not finite. To establish this, we present a procedure for determining the norm of the vacuum in any quantum field theory. With the Dirac norm of the vacuum of the second-order-derivative plus fourth-order-derivative theory not being finite, the Feynman rules that are used to establish renormalizability are not valid, as is the assumption that the theory can be used as an effective theory at energies well below the Planck scale. This lack of finiteness is also manifested in the fact that the Lorentzian path integral for the theory is divergent. Because the vacuum Dirac norm is not finite, the Hamiltonian of the theory is not Hermitian. However, it turns out to be $PT$ symmetric. When one continues the theory into the complex plane and uses the $PT$ symmetry inner product, viz. the overlap of the left-eigenstate of the Hamiltonian with its right-eigenstate, one then finds that for the vacuum this norm is both finite and positive, the Feynman rules now are valid, the Lorentzian path integral now is well behaved, and the theory now can serve as a low energy effective theory, one that we show to have a real classical gravity limit. Consequently, the theory can now be offered as a fully consistent, unitary and renormalizable theory of quantum gravity.

A recent quantum-geometrical approach for the possible reconciliation of the principles of general relativity and quantum mechanics extends the fundamental tensor to the relativistic (quantum) scales, in which additional geometric structures and curvatures, i.e., additional sources of gravitation, are emerged. This paper introduces some characteristics of the emerged curvatures and their consequences on regulating the space and initial singularities. We analyze the timelike geodesic congruence in the simplest solutions of the Einstein field equations; the homogeneous, isotropic, and spherically symmetric Schwarzschild, de Sitter–Schwarzschild, and Friedmann–Lemaitre–Robertson–Walker (FLRW) metrics. From the expansion of the trajectory congruence that follows the change in the shape of the volume which keeps the same set of geodesics in the bundle along the flow lines which are generated by the velocity fields, we conclude that the analytical and numerical analyses give an unambiguous signature that the space and initial singularities are attenuated or even regulated, especially in the relativistic (quantum) regime. This means that the regulation of the singularity in Einstein’s general relativity (GR) would not be possible until quantum-mechanical ingredients are properly imposed on it.

We study the periapsis shift of a quasi-circular orbit in general static spherically symmetric spacetimes. We derive two formulae in full order with respect to the gravitational field, one in terms of the gravitational mass $m$ and the Einstein tensor and the other in terms of the orbital angular velocity and the Einstein tensor. These formulae reproduce the well-known ones for the forward shift in the Schwarzschild spacetime. In a general case, the shift deviates from that in the vacuum spacetime due to a particular combination of the components of the Einstein tensor at the radius $r$ of the orbit. The formulae give a backward shift due to the extended-mass effect in Newtonian gravity. In general relativity, in the weak-field and diffuse regime, the active gravitational mass density, ${\rho }_A=(ϵ+p_r+2p_t)/c^2$, plays an important role, where $ϵ$, $p_r$ and $p_t$ are the energy density, the radial stress and the tangential stress of the matter field, respectively. We show that the shift is backward if ${\rho }_A$ is beyond a critical value ${\rho }_c\simeq 2.8\times 10^{-15}$g/cm³${(m/M_{\odot })}^2{(r/\mathrm{\text{a.u.}})}^{-4}$, while a forward shift greater than that in the vacuum spacetime instead implies ${\rho }_A<0$, i.e. the violation of the strong energy condition, and thereby provides evidence for dark energy. We obtain new observational constraints on ${\rho }_A$ in the Solar System and the Galactic Centre.

This study has established the stability of Reissner–Nordström black holes within a specific parameter range against charged scalar perturbations. Additionally, the near-extremal Reissner–Nordström black holes exhibit a phenomenon known as the Schwinger effect for black holes, involving the production of charged scalar particles. This paper explores the stability and Schwinger effect in the context of static charged black holes within the Einstein–ModMax theory. Our approach closely aligns with the existing literature methods. We aim to investigate how the nonlinearity inherent in the theory may impact both the stability regime and the rate of charged scalar pair production by the black hole.

We examine the cosmic scenario of interacting Kaniadakis holographic dark energy in dynamical Chern–Simons modified gravity and the fractal universe. For this purpose, the Hubble, deceleration, coincidence, equation-of-state and jerk parameters have been evaluated in view of the redshift parameter. It is observed that deceleration parameter $(q)$ evaluates the accelerated expansion of the universe in both gravities. The coincidence parameter $(u)$ exhibits the transition of behavior from dark matter to dark energy era of the universe. The behavior of the equation-of-state parameter $({\omega }_{\theta })$ describes the quintessence and vacuum regions of the universe in both gravities for maximum choices of the interacting parameters. The jerk parameter shows the correspondence of the given model with $\mathrm{\Lambda }$CDM model and other standard models in both gravities. All the parameters exhibit consistent behavior with the Planck 2018 data. We also analyze the dynamical stability in both frameworks by formulating dynamical models in the form of a system of differential equations and evaluating their corresponding critical points. Critical points of both models are stable and phase plots indicate attractor behavior that implies stability of the models. Further, stability conditions of both models signify the accelerating expansion of the universe. In addition, we discuss the thermodynamics of this model with the generalized second law and find its validity in both frameworks.