Gravitation and Cosmology最新文献

The Hořava–Lifshitz mixmaster cosmological model near the cosmological singularity is presented as a generalized Euclidean Toda chain. Restricting to dominant vectors of the spectrum, we get a truncated model that qualitatively well describes the mixmaster model. The truncated model is associated with an affine Kac–Moody Lie algebra (A_{2}^{+}). According to the Adler–van Moerbeke criterion, the truncated Hamiltonian system is algebraically completely integrable.

Various calculations carried out in the past to understand the propagation of light in a rotating gravitational field (viz., Kerr field) are examined. For a plane-polarized light, it is observed that due to the effect of rotational gravitational field, the polarization vector of light gets rotated, with the amount of rotation independent from the frequency of the light. In the present work, using the formulations of geometrical optics, I try to find the implications of such findings, which seem to be very strange and give rise to violation of Lorentz Invariance and the Equivalence Principle, which are mostly not accepted by present-day physics. The analysis involves splitting plane-polarized light into left and right circularly polarized components, and then one finds that these two components (with a given frequency) travel with two different velocities in the Kerr field. Also, for an individual circularly polarized component, the velocity of propagation depends on the frequency of light. Assuming the two opposite directions of circularly polarized light to represent two opposite photon spin states, the line element for circularly polarized light is found to depend on the photon spin in addition to frequency. Additional calculations are made to estimate the propagation time delay between two circularly polarized components (with given frequency) between the source and observer at finite distances from the Kerr mass. Some typical estimates of this time delay are made for the Sun and one pulsar, so that in the future one can experimentally verify these results. For an individual circularly polarized component, time delay expressions are also derived for the propagation of light at two different frequencies. It has been found that circularly polarized light with higher frequency (energy) travels faster in a rotating gravitational field as compared to its lower frequency counterpart.

A first introduction is presented to the comparison between classical and relativistic gravitational effects related to planetary shape characterization. The Earth and the giant planets are the examples considered. The analysis is mainly devoted to relativistic and classical predictions of periastron shifts for equatorial or almost equatorial orbits around the Earth and the giant planets, which can be used as tools for determinations of the shape and density distribution. The ratios between relativistic (up to the Lense–Thirring order correction) and classical (resulting from the harmonic expansion) effects and their dependence on the orbit parameters are analyzed in order to identify the conditions improving the possibility to resolve mixed effects. In a complementary approach, predictions for freely falling test particles from relativistic corrections and classical harmonic expansions of the Earth and other planets are compared within the same shape characterization framework.

In 1965, Penrose introduced the idea of a trapped surface which became an essential concept in proving the first singularity theorem. In this work, some neglected aspects of trapped surfaces are considered. Specifically, I discuss that the existence of such a surface in space-time may result in an undesirable consequence: either space-time is singular, or chronology violation arises. Although a trapping region often implies a singularity in space-time, but a singular space-time may not contain any trapped region. Finally, I show that noncosmological trapped surfaces are observer-dependent. It means that some observers in a trapped region may not observe trapped surfaces!

We present the images of binary black holes (BHs) using the Majumdar–Papapetrou multi-BH solution, depending on the parameters of the problem: the BH masses, the distance between them, and the inclination of the observer. The images consist of shadows and photon rings. We find that a photon ring structure appears between the BHs. The trajectories of photons are calculated.

In physics and cosmology, scalar fields are considered basic. In this study, we are interested to inspect the conduct of massless scalar field (SF) and massive scalar field (MSF) models in (f(R,T)) theory for Bianchi-I universe models. We discuss two cosmological models with respect to late cosmic acceleration, using constant scalar potential and exponential scalar potential models. Also, we study the behavior of a massive scalar field. Finally, we obtain our results in (f(R,T)) and general relativity (GR). In addition, we obtained an LRS Bianchi-I metric as a result of the solutions we made and selection of special constants.

Acoustic space-times have been known to offer analogue models for black hole physics and cosmology. Within this context, aspects of analogue quantum field theories in curved space-time are studied. In particular, some new comments have been made on the analogue Hawking temperature including a quick derivation of the result. Further, analogue cosmology is explored, within which an acoustic version of the Parker–Toms model is proposed, and the corresponding quantities are calculated. The limits of the acoustic analogue are emphasized.

The influence of the gravitational fields of pulsars and magnetars on the emission of arions (strictly massless pseudoscalar Goldstone particles) during propagation of magnetodipole waves in a constant magnetic field has been evaluated. The solution of the equation was obtained, and the flux of arions emitted by magnetodipole waves during their propagation in a constant magnetic field was found. It has been shown that the amplitude of a created arion wave at a distance from the source of magnetodipole radiation of a pulsar or magnetar, ((rtoinfty)), in the considered case tends to a constant value. The intensity of arion emission in a solid angle element and the amount of arion energy (overline{I}), emitted in all directions per unit time grow quadratically with increasing distance traveled by the magnetodipole radiation of a pulsar or magnetar in a constant magnetic field. Such growth of the energy is due to the fact that the constant magnetic field is defined in the whole space. In reality, the galactic and intergalactic magnetic fields can exist in this form only in finite regions of space, outside which the force lines of their induction vector are curved. Therefore, it is possible to apply these results only in a region of space for which (rleq L_{textrm{coh}}<infty), where (L_{textrm{coh}}) is the coherence length, the distance at which the force lines of the induction vector can be considered to be straight. An estimate for the value of the coupling constant of photons with arions is obtained.

Based on the previously formulated theory of spherical perturbations in the cosmological medium of self-gravitating scalarly charged fermions with the Higgs scalar interaction and the similarity properties of such models, the formation of supermassive black hole (SMBH) seeds in the early Universe is studied. Using numerical simulation of the process, it is shown that the mass of SMBH seeds during the evolution process reaches a limiting value, after which it begins to slowly fall. The possible influence of nonlinearity on this process is discussed.

If we look from a quantum perspective, the most natural way in which the universe can be created is in entangled pairs whose time flow is oppositely related. This suggests the idea of the creation of a universe-antiuniverse pair. Assuming the validity of this hypothesis, in this paper, we show that the universe expands in an accelerated manner. The same reasoning holds for the anti-universe as well. This idea does not require any form of dark energy as used in the standard cosmological model (Lambda)CDM or in modified theories of gravity.