Gravitation and Cosmology最新文献

We consider the essence of the well-known discussion between Bohr and Einstein (1935), which concerned the completeness of quantum mechanics. If one followed Bohr, then the wave function would give the probability description of an individual particle. However, Einstein considered the wave function as an instrument for describing the statistical ensemble of identical particles—solitons. On the other hand, Wiener found the special (alpha)-representation of quantum mechanics, for which the wave function appeared to be an element of the random Hilbert space with normal dispersion. This fact proves the equivalence of Bohr’s and Einstein’s positions, the central limiting theorem being taken into account. Also the dark matter hypothesis and new possibilities of the Brioschi 16-spinor realization of the Skyrme–Faddeev chiral model are discussed, including the neutrino oscillation problem.

We revisit the (alpha)-Starobinsky inflation, also known as the (E)-model, in the light of current CMB and LSS observations. The inflaton potential in the Einstein frame for this model contains a parameter (alpha) in the exponential, which alters the predictions for the scalar and tensor power spectra of Starobinsky inflation. We obtain these power spectra numerically without using the slow-roll approximation, and perform MCMC analysis to put constraints on the parameters (M) and (alpha) from Planck-2018, BICEP/Keck (BK18) and other LSS observations. We consider the general reheating scenario by varying the number of e-foldings during inflation, (N_{textrm{privot}}), along with other parameters. We find (log_{10}alpha=0.0^{+1.6}_{-5.6}), (log_{10}M=-4.91^{+0.69}_{-2.7}), and (N_{textrm{privot}}=53.2^{+3.9}_{-5}) with (95%) C.L. This implies that the present CMB and LSS observations are insufficient for constraining the parameter (alpha). We also find that there is no correlation between (N_{textrm{privot}}) and (alpha).

We discuss theoretical and experimental foundations of the hypothesis on the origin of magnetic fields of the Earth and other astrophysical objects, proposed in the early 20th century by W. Sutherland, A. Einstein, and independently by Yu.S. Vladimirov. According to this hypothesis, the electric charges of the electron and proton slightly differ in magnitude, leading to the emergence of magnetic fields in rotating astrophysical objects. A theoretical justification of the Sutherland–Einstein hypothesis is presented in a simplified version of the 6D Kaluza–Klein theory, taking into account the consequences of the Kerr–Newman metric. The analysis shows that a fundamental dipole-type magnetic field should arise around any massive rotating body. However, in real astrophysical objects, such a field is largely screened and distorted by induced charges and currents. As an application, we consider the problem of determining the magnetic fields of hot Jupiters, since strong tidal effects in these giant exoplanets should result in approximately similar screening mechanisms.

The presence of a tachyon field in (R+mu R^{2}) theory is considered. Our analysis shows that the tachyon field contribution to the energy density is suppressed, but it affects cosmological parameters; in particular, the spectral index is modified. This model is in agreement with Panck2018 data for some parameter ranges.

We present new exact solutions to the Einstein–Cartan (EC) field equations for static, spherically symmetric configurations of a noncharged Weyssenhoff fluid in isotropic coordinates, derived using the extended technique of differential forms applied to the non-Riemannian space-time of the Einstein–Cartan theory of gravitation (ECTG). The solutions exhibit regular behavior with nonnegative pressure and energy density, and satisfy the adiabatic stability condition ({1/sqrt{3}<a<1}). All models are rotating and accelerating, with vanishing expansion and shear. Spin contributions explicitly influence the matter distribution; in the spinless limit, the solutions reduce to those of Narlikar and Kuchowicz. For specific parameter values (n) ((sqrt{2}leq nleq 2)), the models may be applicable to neutrino geodesic motion and other compact object studies in EC gravity.

We present a brief review of known analytic results for quasinormal modes (QNMs) of black holes and related space-times. We consider regimes in which the perturbation equations admit exact or perturbative solutions, providing insights complementary to numerical or semi-analytic approaches. We discuss solvable cases in lower-dimensional space-times, algebraically special modes, and exact results in higher-curvature gravity theories. Particular attention is given to the eikonal mode and its correspondence with null geodesics, as well as to beyond-eikonal approximations based on inverse multipole expansions  in parametrized metrics. We review analytic solutions obtained in the near-extremal limit of Schwarzschild–de Sitter black holes, in the regime of large field mass, and in pure de Sitter and anti–de Sitter space-times, where boundary conditions play a crucial role. Being not exhaustive, this overview highlights the diversity of techniques and physical insights made possible by analytic treatments of quasinormal spectra.

Levels of quantization in gravity theory have been classified. Objects and processes in gravitationally bound systems and their general properties are analyzed to create a consistent theory of gravity quantization and to construct quantum models of compact astrophysical objects and the early Universe.

A dilatonic dyonic black hole solution with the gravitational radius (2mu) and two charges (Q_{1}) and (Q_{2}) (electric and magnetic ones) is considered in a gravitational 4D model with one scalar field and one 2-form, with the dilatonic coupling constant (lambda=pm 1/sqrt{2}). Circular null geodesics are explored. The 3rd order polynomial master equation for the radius (R_{0}) of photon sphere is studied. There is only one solution with (R_{0}>2mu). The circular null geodesics are shown to be unstable. The black hole shadow is studied, and relations for the shadow angle and critical impact parameter are obtained.

The Wheeler–DeWitt geometrodynamics, as the first attempt to develop a quantum theory of gravity, faces certain challenges, including the problem of time and interpretation of the wave function. In this paper, we present the extended phase space approach to quantization of gravity as an alternative approach to the Wheeler–DeWitt quantum geometrodynamics. For a space-time with a nontrivial topology, the Wheeler–DeWitt equation loses its sense, but we can derive the Schrödinger equation. Until now, the Schrödinger equation was derived for systems with a finite number of degrees of freedom, and we need to generalize the procedure for field models. The simplest field model is a spherically symmetric one. We derive the integro-differential Schrödinger equation for this model, examine its structure, and find its solution.

The process of detection of Unruh radiation by a screened pointlike monopole detector with a narrow directivity pattern is considered for massive and massless scalar fields in (3+1)D space-time. The corresponding stationary energy-angular dependencies of the screened detector responses to the Unruh radiation are calculated numerically for massive and massless particles and are estimated analytically for massless particles. It is shown that in all cases the response is significantly anisotropic, and its energy profile strongly depends on the shape of the screening function. The corresponding brightness temperature of the observed Unruh radiation may exceed the Unruh temperature by orders of magnitude for a directivity pattern narrow enough. These points confirm that the Unruh radiation cannot be considered as thermal (equilibrium) radiation. The generation of the Unruh radiation is a pair production process that is symmetric and implies the existence of counterpart radiation going to infinity. The spectrum of this outgoing counterpart radiation also depends on the accelerated detector properties and, in principle, can be observed by detectors at rest in an initial Minkowski frame. This may allow one to detect and identify the counterpart radiation in particle accelerators in the future. The interaction of the Unruh radiation with an accelerated screened detector should lead to the emergence of a reaction force acting on this detector.