Пространство, время и фундаментальные взаимодействия @stfi
Статьи журнала - Пространство, время и фундаментальные взаимодействия
Все статьи: 387
Detectors of high-frequency gravitational waves based on the gravitational-optical resonance
Статья научная
In this paper, we consider the possibility of registering relic gravitational waves predicted in cosmological models of the early universe with an additional stage of stiff energy dominance. Differences in the spectrum of relic gravitational waves in these models from the case of standard inflationary models are considered. A method for detecting high-frequency gravitational waves based on gravitational-optical resonance in Fabry-Perot interferometers is proposed. The main parameters of the detector are calculated and the frequency range of relic gravitational waves, which can be registered using the proposed approach, is determined.
Бесплатно
Dynamo-optically active media: new aspects of the Minkowski-Abraham controversy
Статья научная
Based on the covariant variation formalism, two versions of the symmetric effective stress-energy tensor of the electromagnetic field in a dynamo-optically active relativistic media are reconstructed in the framework of the tetrad and aether paradigms, respectively. We show that the energy density scalars and pressure tensors coincide for both versions of the stress-energy tensors, however, the corresponding energy flux four-vectors happen to be different in general case. This mathematical fact adds new arguments into the 100-year-long discussion, which is called Minkowski-Abraham controversy and is connected with the correct definition of the electromagnetic energy flux in a continuous media. We consider three examples: first, the axionically active vacuum; second, the spatially isotropic moving dielectric medium; third, the dynamo-optically active medium. We discuss possible applications of the elaborated formalism.
Бесплатно
Electron scattering on a wormhole in the Born approximation
Статья научная
The wormholes which connect either two distant regions of the same Universe or two universes are one of the intriguing hypothetical objects in the physics of gravitational interaction. For wormholes to be traversable, i.e., to allow a traveler to cross them safely, the wormholes must be filled with exotic matter within the framework of general relativity. In this paper it is shown that under certain conditions the number of electrons elastically scattered on an Ellis-Bronnikov wormhole exceeds the number of electrons of the incident flux. The additional electrons appear as a result of their transition through the wormhole from the opposite side of the catenoid. In other words, a negative pressure is created in the wormhole by means of the flux of electrons directed to the wormhole. This allows us to conclude that the wormhole can be stabilized without exotic matter in this way.
Бесплатно
Статья научная
The equations of cosmological dynamics for inflation models based on scalar-torsion gravity with a non-minimal connection between torsion and scalar field are considered based on a power-law parameterization of the connection between the non-minimal interaction function and the Hubble parameter. Three classes of exact solutions to the equations of cosmological dynamics are obtained, which are the basis for further analysis of the evolution of cosmological perturbations and verification of cosmological models of this type using observational data.
Бесплатно
Exact solutions in Friedmann cosmology with scalar fields
Статья научная
The method of exact analysis of cosmological dynamics at the early inflation stage of the evolution of the Friedman Universe, which is determined by the dynamics of the scalar field for the case of minimal and nonminimalinteraction of the field and curvature is considered in this work. The basis of the method is to reduce theequations of dynamics to the same form for all models. The proposed approach allows us to compare modelsbased on the different theories of gravity.
Бесплатно
Exact solutions in cosmological models with non-minimal coupling of scalar field and torsion
Статья научная
Cosmological inflation models with scalar field based on teleparallel gravity with non-minimal coupling of scalar field and torsion are considered. Solution type obtained in this paper is justified for any Hubble parameter and scalar field evolution. Also, the model with scalar field potenital (𝜑) = 𝑚2 2 𝜑𝑛, relating to chaotic inflation with massive scalar field, is verified by modern restrictions on values of cosmological perturbations parameters.
Бесплатно
Exact solutions in modified gravity theories
Статья научная
In this paper, we have reviewed the limitations in the General Relativity theory and the requirement for geometrical dark energy models. Actions for different geometrical dark energy models have been discussed. Specifically, two matter geometry coupling models within the Einstein-Hilbert action have been investigated. The basic equations leading to the discussion of the dynamical aspects of the Universe are derived and some examples of obtaining exact solutions in these two models are discussed.
Бесплатно
Статья научная
The problem reduction of an evolution modelling of the open Universe for conformally flat space-time metric in Fock’s form to an equivalent problem of a particle movement with an unit mass in a force field is demonstrated. The exact cosmological models filled with a substance and radiation in an approximation of the perfect fluid are found since the Friedman solution by means an introduction of set "mechanical" potentials.In the article the possibility of deriving from the Einstein equations exact cosmological solutions for the open Universe by reduction to the equivalent problem of a mass particle motion in the force field is considered. The cosmological model is filled by substance in an approximation of the perfect fluid with nonzero pressure, generally speaking. The metric of 4D space-time is taken in the Fock form as the metric conformal to the Minkowski metric. This metric has the dependence on one variable. A square of the variable is product of advanced and retarded times.The using of mechanical interpretation of the gravitation equations leads to a possibility of consideration of various mechanics force fields with the subsequent physical interpretation of the found exact cosmological solutions.First of all a movement of a free particle with an unit mass (a mechanical force equals to zero) is considered,i.e. the particle moves on inertia. The fourth degree of discovered law of movement is a conformal factor of the cosmological metric which is conformally flat. This case corresponds to the exact cosmological solution without pressure, coinciding with known the Friedman solution for the open Universe.After that the force field leading to uniformly decelerated motion of a particle is considered. The force potential is taken in the form of linear function. The tangent of a slope angle of the function curve coincides with particle acceleration. Such research leads to the exact cosmological solution asymptotically describing both an incoherent dust, and the ultrarelativistic substance which may be interpreted as an equilibrium radiation.Further a square-law function without a linear term and a constant value is taken as a force potential. Such potential can be interpreted as potential of the free oscillator. The solution of corresponding equation of motion is written down in the form of a cosine function with some initial phase related to the ratio between parameters which define dust-like and ultrarelativistic substance. This conclusion becomes obvious after concidering asymptotic behaviour of pressure and energy density. Besides, the series expansion of a root of the fourth degree from a conformal factor asymptoticly coincides with the law of uniformly decelerated motion in previous case that indicates its particular character.
Бесплатно
Extended Einstein-Dirac-aether theory: Spinor modifications of the dynamic aether kinetic term
Статья научная
In the framework of the Einstein-Dirac-aether theory the extended model is established, in which the backreaction of the spinor field on the unit vector field, describing the dynamic aether, is taken into account. For this purpose, we extended the Jacobson constitutive tensor, which enters the kinetic part of the Lagrangian of the unit vector (aetheric) field, by the terms containing spinor tensors and pseudotensors. The self-consistent system of master equations for the unit vector field, as well as, the spinor and gravitational fields is derived using the variation formalism in the framework of the effective field theory up to the second order in derivatives.
Бесплатно
Extended relativistic non-equilibrium thermostatics of stellar structures with radiation pressure
Статья научная
We establish the extended formalism for description of the static spherically symmetric relativistic non-equilibrium stellar systems in the formation of which the radiation pressure plays the key role. The main concept of this extended formalism inherits the ideas, on which the Israel-Stewart causal thermodynamics is based, but now the unit spacelike four-vector, indicated by the term director, is exploited in addition to the unit timelike medium velocity four-vector. An application of the extended formalism is considered; we analyze the profiles of the non-equilibrium pressure and temperature as the functions of guiding parameters introduced phenomenologically.
Бесплатно
Extragalactic TEV photons and the zero-point vibration spectrum limit
Статья научная
There are observations indicating a possible anomalous transparency of intergalactic space (filled with infrared background light) for extragalactic gamma-rays of very high energy (> 100 GeV). The anomaly is usually associated with effects of some new physics. However, another explanation is possible - as a manifestation relating to a cut-off of the zero-point vibration spectrum. It is assumed that this boundary 𝑈ZV is isotropic in the reference frame, where the cosmic microwave background (CMB) radiation is isotropic, and an estimate is obtained: 𝑈ZV ≈ 7.4TeV. It is noted that the presence of a boundary also leads to an increased beta decay time of accelerated particles with the Lorentz factor > 50 (in the CMB rest frame; in addition to the usual (𝛽)). It is widely believed that the ZV-spectrum continues up to the Planck energy (in natural units, the gravitational constant is related to the square of the Planck length). There is, however, a 5D variant of the Absolute Parallelism theory (AP), free from singularities of solutions, where a large characteristic length appears, which determines the thickness of expanding spherical 𝑆3 shell (a cosmological solution as the longitudinal wave along the radius) in co-moving co-ordinates. Newton’s Law ~ 1/𝑟2 is replaced by 1/𝑟 at distances exceeding 𝐿, and the Planck length (a composite parameter) “arises” from when switching to the conventional energy-momentum scale (where the energy of a photon is its angular frequency). The theory features are briefly exposed - description of 15 polarizations (degrees of freedom), the energymomentum tensor (in prolonged 4th order equations), topological charges and quasi-charges of localized field configurations.
Бесплатно
Falsification of gravity theories from the form of dark spots on black hole images
Статья научная
Visual images of supermassive black holes M87* and SgrA* have been successfully registered recently by the international collaboration Event Horizon Telescope. This registration opens the unique possibility for verification (or falsification) of modified gravity theories in the strong filed limit when gravitational field is dominated over astrophysical factors. This verification is crucially important for physical interpretation of astrophysical and cosmological observations of the Universe and for understanding the physical origin of enigmatic dark matter and dark energy. The accuracy of Event Horizon Telescope is sufficient for demonstration of the quantitative agreement of the obtained dark spot images of both black holes with the General Relativity prediction. In particular, the forms of dark spots on the Event Horizon Telescope images correspond to the fast black hole rotation of the supermassive black holes M87* and SgrA*. Meantime, the Event Horizon Telescope accuracy is insufficient for the verification of the modified gravity theories. In the observable future this verification would be possible in realization of the international project of the Space Observatory Millimetron, which angular resolution in few orders of magnitude exceeds the corresponding one of the Event Horizon Telescope.
Бесплатно
Статья научная
The paper presents a some specific method of the gravitational frequency shift measurement for communication radio signals between the spacecraft and ground tracking stations. It is based on the maximum likelihood algorithm and utilizes the Cram´er-Rao bound to estimate the accuracy of signal parameter determination. It is carried out with the bank of data obtained during the “Radioastron” mission. Attention is concentrated at a compensation of the relativistic Doppler effect and frequency noises of the standards used in the experiment
Бесплатно
Finding the valid gravity theory from observations of black hole silhouettes
Статья научная
Nowadays the major problem in cosmology is in the choice of the valid gravity theory for interpretation of the observational data. Usually in cosmology it is used the Einstein general theory of relativity and the corresponding Friedman-Robertson-Walker equations in the strong field limit (when gravitational potential is of the order of square of the light velocity). Meanwhile, the general theory of relativity is verified and confirmed only in the weak field limit in the nearest cosmological environments. Observations of black hole images (silhouettes) opens a unique possibility for the verification (or falsification) of modified gravity theories in the strong field limit when gravitation dominates over astrophysical or cosmological factors. This is especially crucial for physical interpretation of astrophysical and cosmological observations of the far regions of the Universe and for understanding the physical origin of enigmatic dark matter and dark energy. The first visual images of supermassive black holes M87* and SgrA* have been observed recently by the Event Horizon Telescope. These images demonstrate a qualitative agreement with the general theory of relativity. In the nearest future it would be possible to quantitatively scrutinize the known modified gravity theories after construction of the Space Millimetron Observatory with nano-arcsecond angular resolution.
Бесплатно
Friedmann cosmological model with nonlinear scalar field
Статья научная
This paper is a translation of work Ivanov G.G "Friedmann cosmological model with nonlinear scalar field" of 1981 [1].
Бесплатно
Generalization of the C3 matching procedure
Статья научная
To handle the case in which discontinuities are present along the matching hypersurface, in this work, we present a generalization of the 𝐶3 matching procedure discussed in previous works. It demands that a solution of Einstein’s equations also describe the matching hypersurface.
Бесплатно
Generalized Kaluza-Klein models with Gauss-Bonnet lagrangians
Статья научная
The five-dimensional generalization of Einstein’s theory of gravitation proposed first by Th. Kaluza (1921) and improved a few years later by O. Klein (1926) has led to the Kaluza-Klein model incorporating electromagnetism and gravitation, and a variant of the Brans-Dicke theory of gravity, containing a scalar field interacting with metric tensor field. However, neither of these models did use the possibilities offered by the enlargement of the Einstein-Hilbert variational principle via including the Gauss-Bonnet invariant, which in 5 dimensions is no more a pure divergence, and modifies substantially the equations of motion of the theory. After recalling the basics of the Kaluza-Klein model, including the non-abelian case. we give a short review of multi-dimensional cosmological models with scalar fields generated by gauge fields defined on the structural group, including the generalized lagrangian containing the Gauss-Bonnet term 𝑅𝐴𝐵𝐶𝐷𝑅𝐴𝐵𝐶𝐷-4𝑅𝐴𝐵𝑅𝐴𝐵+𝑅2. Then we turn our attention back to the 5-dimensional Kaluza-Klein model, without scalar field and neglecting gravity, but with variational principle enriched by the Gauss-Bonnet term, This leads, in the Minkowskian space-time, to an interesting variant of non-linear Electrodynamics. After discussing the modified Maxwell’s equations, we show how a toroidal soliton can be constructed, and show that it displays the most essential features of Dirac’s electron: electric charge, magnetic moment, and spin. It also predicts the particle-anti particle symmetry.
Бесплатно
H-spaces (H41,G) of type {41}: projective-group properties
Статья научная
In this paper we study five-dimensional ℎ-spaces (𝐻41, 𝑔) of type {41} [4]. Necessary and sufficient conditions for (𝐻41, 𝑔) to be a space of constant curvature are found. The general solution of the Eisnhart equation in ℎ-space (𝐻41, 𝑔) of non-constant curvature is determined. We establish conditions for the existence of a non-homothetic projective motion in (𝐻41, 𝑔) and describe the structure of a non-homothetic projective Lie algebra in ℎ-space (𝐻41, 𝑔) of type {41}.
Бесплатно
Hyperbolic-logarithmic model of nonlinear electrodynamics
Статья научная
In this paper we consider a new model of nonlinear electrodynamics - "Hyperbolic-logarithmic". This model contain a three parameters and describe by following Lagrangian: ℒ = -ℱ - 𝛽 𝑎𝑟𝑡ℎ(𝛽ℱ) - 2𝛽 [ln(1 + 𝛽ℱ) + ln(1-𝛽ℱ)], where ℱ = 1 4𝐹𝑖𝑘𝐹𝑖𝑘. We show, that in this model dual symmetry is broken. Also we proved that the electric field of a point-like charge becomes non-singular in this framework, static electric energy of this charge is finite. We calculate a theory parameters values guided by electron parameters and Abraham - Lorentz idea about a pure electromagnetic nature of electron mass. We find the canonical and symmetrical Belifante energy momentum tensors.
Бесплатно
Статья обзорная
В данной статье представлен обзор работы III летней международной молодежной школы «Гравитация, космология и астрофизика», посвященной памяти академика РАН В.И. Пустовойта.
Бесплатно
