General Relativity and Gravitation最新文献

Quantum gravity has been baffling the theoretical physicist for decades now, both for its mathematical obscurity and phenomenological testing. Nevertheless, the new era of precision cosmology presents a promising avenue to test the effects of quantum gravity. In this study, we consider a bottom-up approach. Without resorting to any candidate quantum gravity, we invoke a generalized uncertainty principle (GUP) directly into the cosmological Hamiltonian for a universe sourced by a phantom scalar field with potential to study the evolution of the universe in a very early epoch. This is followed by a systematic analysis of the dynamics, both qualitatively and quantitatively. Our qualitative analysis shows that the introduction of GUP significantly alters the existence of fixed points for the potential considered in this paper. In addition, we confirm the existence of an inflationary phase and analyze the behavior of relevant cosmological parameters with respect to the strength of the GUP distortion.

We consider a homogeneous and isotropic spacetime having a space of positive curvature and study the cosmic evolution of dynamical vacuum energy. We utilize the dynamical system technique to study the existence of fixed points and their corresponding stability in model. The corresponding cosmological solutions describe late-time accelerating universe having decelerating era composed of radiation and matter-dominated phase. The numerical integration of autonomous system reveals that the cosmological solutions of dynamical vacuum energy model may describe the cosmic history of universe. As a consequence of the dynamical vacuum energy in closed Friedmann-Robertson-Walker model, the trajectories between fixed points in the phase space would also correspond to the bouncing and turnaround universe evolution.

In this paper, we study the dynamics of a test particle around a regular black hole (BH) in a non-minimal Einstein-Yang-Mills (EYM) theory and examine the BH shadow. The EYM theory is a non-minimally coupled theory in which curvature couples to non-Abelian gauge fields. We investigate particle motion with parameters in EYM BH for massless and massive particles. This work provides the horizon structure, photon radius and inner stable circular orbit (ISCO) of a mass particle with EYM BH parameters. An analysis is provided of the effective potential as well as the possible orbits for test particles under various EYM BH parameters values. In timelike radial geodesics, we find that for smaller values of magnetic charge, particles following a timelike radial geodesic are more hasty in EYM BH, and hence arrive at the center faster than those traveling a Schwarzschild BH geodesic. However, at larger values of the magnetic charge, the inverse effect is observed. The effect of model parameters is investigated in order to study the ISCO, photon radius, orbit stability (Lyapunov exponent), and effective force on particles for the BH in the EYM theory. Finally, we investigate the BH shadow. We find that higher magnetic charge values and non-minimal coupling parameters result in smaller shadow radius values.

We study the dynamical effects of the non-coincidence gauge on the geometric dark energy within the framework of (fleft( Qright) )-gravity. We specifically examine a spatially flat Friedmann–Lemaître–Robertson–Walker universe with a dust fluid source, employing (fleft( Qright) )-theory of gravity. Our goal is to analyze the dynamical evolution of cosmological parameters to reconstruct the cosmological history. We reproduce previous findings; nevertheless due to the presence of the dust fluid, new asymptotic solutions exist. We emphasize the significance of selecting the appropriate connection, as it dramatically change the cosmological dynamics. Additionally, we show that for the simple power-law (fleft( Qright) ) model, there exist a non-coincidence connection where the field equation reconstruct the main epochs of the cosmological history, that is, inflation, radiation epoch, matter era and the late-time acceleration is attributed to the de Sitter solution, which is the unique attractor of the solution trajectories. Moreover this model support Big Rip singularities as unstable solutions in the past.

External non-minimally coupled scalar and spinor field perturbations have been studied in a (1 + 1) dimensional dilatonic blackhole spacetime (Mandal et al. in Mod Phys Lett A 6:1685–1692. https://doi.org/10.1142/S0217732391001822, 1991; Witten in Phys Rev D 44:314–324. https://doi.org/10.1103/PhysRevD.44.314, 1991). Exact analytical expressions of the quasi-normal mode frequencies have been found for both the cases. In the scalar perturbations the quasi-normal mode frequencies turn out to be purely imaginary and negative. Furthermore we have found that the quasi-normal frequencies for Dirac field exhibit both real and imaginary part. The QNM frequencies decay monotonically with the overtone number under certain class of the blackhole parameters. The decay profile ensures the stability of the blackhole spacetime under these perturbations.

In this letter, we show that the Semiclassical Einstein’s Field Equation can be recovered using the generalized entropy (S_{gen}). This approach is reminiscent of non-equilibrium thermodynamics. Furthermore, contrary to the entanglement equilibrium approach of deriving the semiclassical Einstein’s equation, this approach does not require any such assumptions and still recovers its correct form. Therefore, in a sense, we also show the validity of the semiclassical approximation, a crucial approach for establishing a number of important ideas such as the Hawking effect.

In the Standard Model of particle physics, the mass of the Higgs particle can be linked to the scale at which the Standard Model breaks down due to a Landau pole/triviality problem: for a Higgs mass somewhat higher than the measured value, the Standard Model breaks down before the Planck scale. We take a first step towards investigating this relation in the context of causal set quantum gravity. We use a scalar-field propagator that carries the imprints of spacetime discreteness in a modified ultraviolet behavior that depends on a nonlocality scale. We investigate whether the modification can shift the scale of the Landau pole in a scalar field theory with quartic interaction. We discover that the modifications speed up the onset of the Landau pole considerably, so that the scale of new physics occurs roughly at the nonlocality scale. Our results call into question, whether a separation between the nonlocality scale and the discreteness scale, which is postulated within causal set quantum gravity, and which has been argued to give rise to phenomenological consequences, is in fact achievable. Methodologically, our paper is the first to apply continuum functional Renormalization Group techniques in the context of a causal-set inspired setting.

We investigate complex quaternion-valued exterior differential forms over 4-dimensional Lorentzian spacetimes and explore Weyl spinor fields as minimal left ideals within the complex quaternion algebra. The variational derivation of the coupled Einstein–Weyl equations from an action is presented, and the resulting field equations for both first and second order variations are derived and simplified. Exact plane symmetric solutions of the Einstein–Weyl equations are discussed, and two families of exact solutions describing left-moving and right-moving neutrino plane waves are provided. The study highlights the significance of adjusting a quartic self-coupling of the Weyl spinor in the action to ensure the equivalence of the field equations.

Recent investigations revealed that the near horizon Hamiltonian of a massless, chargeless outgoing particle, for its particular motion in static as well as stationary black holes, is effectively (sim xp) kind. This is unstable by nature and has the potential to explain a few interesting physical phenomena. From the path integral kernel, we first calculate the density of states. Also, following the idea of Singh and Padmanabhan (Phys Rev D 85:025011, 2012. https://doi.org/10.1103/PhysRevD.85.025011. arXiv:1112.6279 [hep-th]) here, in the vicinity of the horizon, we calculate the effective path corresponding to its Schrodinger version of Hamiltonian through the path integral approach. The latter result appears to be complex in nature and carries the information of escaping the probability of the particle through the horizon. In both ways, we identify the correct expression of Hawking temperature. Moreover, here we successfully extend the complex path approach to a more general black hole like Kerr spacetime. We feel that such a complex path is an outcome of the nature of near horizon instability provided by the horizon and, therefore, once again bolstered the fact that the thermalization mechanism of the horizon may be explained through the aforesaid local instability.

Searching for variations in dimensionless physical constants presents a meaningful characteristic in experimental and observational studies. One of the most valuable explorations of these variations could depend on the evolution of white dwarf stars. By analyzing the spectrum of the white dwarf star G191-B2B, we derive a robust limit on the cosmological variation of the gravitational constant: (dot{mathrm{G}}/mathrm{G}=(0.238pm 2.959)times {10}^{-15}{mathrm{yr}}^{-1}). This limit proposes a potential test of the framework of modern unification theories.