Searcharxiv⌕ Search

arXiv subjects

S. L. Cherkas

Publications and source records attributed to S. L. Cherkas.

At least 19 recordsLinked to original sources
arXiv2021

Wave optics of quantum gravity for massive particles

Effects of the quantum gravity under Minkowski space-time background are considered. It is shown that despite the absence of the complete theory of quantum gravity, some concrete predictions could be made for the influence of the quantum gravitational fluctuations on the propagation of the massive particles. We demonstrate that although the gravitational potential fluctuations do not produce particle scattering, they cause decoherence of the matter waves due to off-shell effects. For point-like massive particles of the Planck mass order, the effect is considerable. However, this type of decoherence is beyond the measurable possibility for the real particles of the finite size.

gr-qc↗
arXiv2021

Cosmological singularity as an informational seed for Everything

It is shown how to place some amount of matter into the cosmological singularity and to encode its state. A free and massless scalar field is considered as a prototype of matter. Two different but coherent approaches to this issue are presented. The expression for the scalar particles' spectral energy density, which is initially encoded at the singularity, is deduced. An informational aspect of the problem is discussed.

physics.gen-ph↗
arXiv2020

Reference level of the vacuum energy density of the Universe and astrophysical data

An extended framework of gravity, in which the first Friedmann equation is satisfied up to some constant due to violation of gauge invariance, is tested against astrophysical data: Supernovae Type-Ia, Cosmic Chronometers, and Gamma-ray bursts. A generalized expression for the Friedmann equation, including the possible vacuum contributions, is suggested, and two particular cosmological models with two independent parameters are considered within this framework and compared on the basis of the likelihood analysis. One of the models considered includes contribution of the residual vacuum fluctuations to the energy density and places the limit on the UV cutoff scale as $k_{max} = 12.43^{+0.9}_{-1.6} [M_p/\sqrt{2+N_{sc}}]$, where $N_{sc}$ is the number of minimally coupled scalar fields. Model comparison using the Akaike information criteria and Bayesian evidence shows a preference for the conventional $Λ$CDM over the extended models. A more general model with three parameters is considered within which an anti-correlated behavior between the dynamical vacuum fluctuations contribution and a negative cosmological constant was found. The result is an upper limit of $Ω_Λ \lesssim -0.14$ at $95\%$ C.L., which is only mildly disfavored ($\ln\mathcal{B} = -1.8$) with respect to $Λ$CDM.

physics.gen-ph↗
arXiv2020

The equation of vacuum state and the structure formation in universe

The vacuum is considered as some fluid emergent from the zero-point fluctuations of the quantum fields contributing to the vacuum energy density and pressure. The equation of vacuum state and the speed of vacuum sound-waves are deduced under the assumption of zero vacuum entropy. The evolution of the background space-time metric resembles that of the Milne's-like universe. In the framework of the five-vector theory of gravitation allowing an arbitrary choice of the energy density reference level, the dynamics of the vacuum, pressureless matter, and space-time metrics perturbations are traced under this background. The obtained results show the very early formation of the Universe structure without the need for dark matter. Thus, a vacuum can be considered as some of the dark-energy-matter unification.

gr-qc↗
arXiv2020

Evidence of time evolution in quantum gravity

We argue that the problem of time is not a crucial issue inherent in the quantum picture of the universe evolution. On the minisuperspace model example with the massless scalar field, we demonstrate four approaches to the description of quantum evolution, which give similar results explicitly. The relevance of these approaches to building a quantum theory of gravity is discussed.

gr-qc↗
arXiv2019

Theory of gravity admitting arbitrary choice of the energy density reference level

Five-vectors theory of gravity is proposed, which admits an arbitrary choice of the energy density reference level. This theory is formulated as the constraint theory, where the Lagrange multipliers turn out to be restricted to some class of vector fields unlike the General Relativity (GR), where they are arbitrary. The possible cosmological implication of the model proposed is that the residual vacuum fluctuations dominate during the whole evolution of the universe. That resembles the universe having a nearly linear dependence of scale factor on cosmic time.

gr-qc↗
arXiv2018

Plasma Perturbations and Cosmic Microwave Background Anisotropy in the Linearly Expanding Milne-like Universe

We expose the scenarios of primordial baryon-photon plasma evolution within the framework of the Milne-like universe models. Recently, such models find a second wind and promise an inflation-free solution of a lot of cosmological puzzles including the cosmological constant one. Metric tensor perturbations are considered using the five-vectors theory of gravity admitting the Friedmann equation satisfied up to some constant. The Cosmic Microwave Background (CMB) spectrum is calculated qualitatively.

gr-qc↗
arXiv2018

Matter creation and primordial CMB Spectrum in the inflationless Milne-like cosmologies

We present a new insight into the interpretation of the primordial spectrum of scalar particles density perturbations. On the assumption of spectrum universality, i.e., that the mean energy density and the typical value of inhomogeneity can be chosen arbitrarily in the framework of the model considered, the form of the spectrum becomes completely defined. It is close to the flat Harrison-Zeldovich spectrum, but with the suppressed low-frequency modes.

gr-qc↗
arXiv2016

Quantum mechanics allows setting initial conditions at a cosmological singularity: Gowdy model example

It is shown that the initial conditions in the quasi-Heisenberg quantization scheme can be set at the initial cosmological singularity per se. This possibility is provided by finiteness of some quantities, namely momentums of the dynamical variables, at a singularity, in spite of infinity of the dynamical variables themselves. The uncertainty principle allows avoiding a necessity to set values of the dynamical variables at singularity, as a wave packet can be expressed through the finite momentums. Influence of the initial condition set in the singularity in such a way to a number of gravitons under a vacuum state, arising during later evolution, is investigated. It is shown that, even choosing of some special state at the singularity minimizing late time expansion rate, some amount of gravitons still appear in the late time evolution.

gr-qc↗
arXiv2014

Solution of the discrete Wheeler-DeWitt equation in the vicinity of small scale factors and quantum mechanics in the space of negative constant curvature

The asymptotic of the solution of the discrete Wheeler-DeWitt equation is found in the vicinity of small scale factors. It is shown that this problem is equivalent to the solution of the stationary Schrödinger equation in the (super) space of negative constant curvature. The minimum positive eigenvalue is found from which a continuous spectrum begins.

gr-qc↗
arXiv2014

Quantization of the inhomogeneous Bianchi I model: quasi-Heisenberg picture

The quantization scheme is suggested for a spatially inhomogeneous 1+1 Bianchi I model. The scheme consists in quantization of the equations of motion and gives the operator (so-called quasi-Heisenberg) equations describing an explicit evolution of a system. Some particular gauge suitable for quantization is proposed. The Wheeler-DeWitt equation is considered in the vicinity of zero scale factor and it is used to construct a space, where the quasi-Heisenberg operators act. Spatial discretization as a UV regularization procedure is suggested for the equations of motion.

gr-qc↗
arXiv2012

Can the scale factor be rippled?

We address an issue: would the cosmological scale factor be a locally oscillating quantity? This problem is examined in the framework of two classical 1+1-dimensional models: the first one is a string against a curved background, and the second one is an inhomogeneous Bianchi I model. For the string model, it is shown that there exist the gauge and the initial condition providing an oscillation of scale factor against a slowly evolving background, which is not affected by such an oscillation "at the mean". For the inhomogeneous Bianchi I model with the conformal time gauge, an initially homogeneous scale factor can become inhomogeneous and undergo the nonlinear oscillations. As is shown these nonlinear oscillations can be treated as a nonlinear gauge wave.

gr-qc↗
arXiv2012

An inhomogeneous toy-model of the quantum gravity with explicitly evolvable observables

An inhomogeneous (1+1)-dimensional model of the quantum gravity is considered. It is found, that this model corresponds to a string propagating against some curved background space. The quantization scheme including the Wheeler-DeWitt equation and the "particle on a sphere" type of the gauge condition is suggested. In the quantization scheme considered, the "problem of time" is solved by building of the quasi-Heisenberg operators acting in a space of solutions of the Wheeler-DeWitt equation and the normalization of the wave function corresponds to the Klein-Gordon type. To analyze the physical consequences of the scheme, a (1+1)-dimensional background space is considered for which a classical solution is found and quantized. The obtained estimations show the way to solution of the cosmological constant problem, which consists in compensation of the zero-point oscillations of the matter fields by the quantum oscillations of the scale factor. Along with such a compensation, a slow global evolution of a background corresponding to an universe expansion exists.

gr-qc↗
arXiv2010

Cosmological production of fermions in a flat Friedman universe with linearly growing scale factor: exactly solvable model

We consider an exactly solvable model for production of fermions in the Friedman flat universe with a scale factor linearly growing with time. Exact solution expressed through the special functions admit an analytical calculation of the number density of created particles. We also discuss in general the role of the phenomenon of the cosmological particle production in the history of universe.

gr-qc↗
arXiv2007

Quantum mechanics of the closed collapsing Universe

Two approaches to quantization of Freedman's closed Universe are compared. In the first approach, the Shrodinger's norm of the wave function of Universe is used, and in the second approach, the Klein-Gordon's norm is used. The second one allows building the quasi-Heisenberg operators as functions of time and finding their average values. It is shown that the average value of the Universe scale factor oscillates with damping and approaches to some constant value at the end of the Universe evolution.

gr-qc↗
arXiv2007

Universe driven by the vacuum of scalar field: VFD model

It is shown that in the Vacuum Fluctuations Domination model (VFD), where vacuum fluctuations of scalar fields dominates under matter and radiation throughout the all history of the Universe expansion (arXiv:gr-qc/0604020, arXiv:gr-qc/0610148), acceleration parameter evolves monotonically from the zero to the present day negative value. That is according to this model the Universe has no decelerating past and conventional radiation domination and matter domination epochs are absent. Predictions of accelerating parameter for z~0-2 is compared with that follows from the SN type Ia data.

astro-ph↗