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V. K. Dubrovich

Publications and source records attributed to V. K. Dubrovich.

At least 19 recordsLinked to original sources
arXiv2023

The Metron Project -- I. The Metron Project Science Program

In this paper, the first in a series of four articles, the scientific goals of the Metron project are highlighted, and the characteristics of the cosmic objects available for study within its framework are provided. The Metron interferometer radio telescope should include arrays of meter-range dipole antennas placed on Earth, in outer space or on the far side of the Moon (or a combination of these options). Working in the meter range will enable the study of the so-called cosmological epoch of ``Dark Ages'', which is challenging to observe but highly interesting for understanding the origin of the first stars, galaxies, and black holes, as well as for the search for new cosmological objects and processes. One possibility is to search for absorption in the 21 cm line within extended halos around early protogalaxies and supermassive primordial black holes, whose existence is predicted in a number of models. Another goal of Metron may be to clarify the anomalous absorption in the 21 cm line previously detected by the EDGES telescopes and to observe radio emissions from stars' and exoplanets' magnetospheres. The Metron project aims to achieve unprecedented resolution for the meter range, which is expected to yield new world-class scientific results. Meter-range antennas and receivers are relatively simple and inexpensive, and the construction of interferometric arrays from them can be accomplished in a relatively short period of time.

astro-ph.CO↗
arXiv2021

Production and evaporation of micro black holes as a link between mirror universes

It is shown that the equalization of temperatures between our and mirror sectors occurs during one Hubble time due to microscopic black hole production and evaporation in particle collisions if the temperature of the Universe is near the multidimensional Plank mass. This effect excludes the multidimensional Planck masses smaller than the reheating temperature of the Universe ($\sim10^{13}$ GeV) in the mirror matter models, because the primordial nucleosynthesis theory requires that the temperature of the mirror world should be lower than ours. In particular, the birth of microscopic black holes in the LHC is impossible if the dark matter of our Universe is represented by baryons of mirror matter. It excludes some of the possible coexisting options in particle physics and cosmology. Multidimensional models with flat additional dimensions are already strongly constrained in maximum temperature due to the effect of Kaluza-Klein mode (KK-mode) overproduction. In these models, the reheating temperature should be significantly less than the multidimensional Planck mass, so our restrictions in this case are not paramount. The new constraints play a role in multidimensional models in which the spectrum of KK-modes does not lead to their overproduction in the early Universe, for example, in theories with hyperbolic additional space.

astro-ph.CO↗
arXiv2020

Observational manifestations of "cosmological dinosaurs'' at redshifts $z\sim20$

We consider a primordial black hole of very high mass, $10^9-10^{10}M_\odot$, surrounded by dark matter and barionic halo at redshifts $z\sim20$ without any local sources of energy release. Such heavy and concentrated objects in the early universe were previously called ``cosmological dinosaurs''. Spectral distribution and spatial variation of the brightness in the 21 cm line of atomic hydrogen are calculated with the theory of radiation transfer. It is shown that a narrow and deep absorption arises in the form of the spherical shell around the primordial black hole at the certain radius. The parameters of this shell depend almost exclusively on the mass of the black hole. The hardware and methodological aspects of the search for such objects are discussed.

astro-ph.CO↗
arXiv2016

Local Bursts Model of CMB Temperature Fluctuations: Scattering in Resonance Lines of Primordial Hydrogen and Helium

Within the framework of a flat cosmological model a propagation of an instantaneous burst of isotropic radiation is considered from the moment of its beginning at some initial redshift z0 to the moment of its registration now (at z=0). We take into account Thomson scattering by free electrons and scattering in La and Lb lines of primordial hydrogen and in lines 1s2 - 1s2p, 1s3p (1S-1P*) of HeI. It is shown that relative amplitude of spectrum distortions caused by scattering in these lines may be from 1000 to 10000 times greater than maximum possible amplitude due to scattering in subordinate lines considered in our previous paper (Dubrovich, Grachev, 2015). In a linear approximation on the optical thickness in the lines the profiles of distortions in resonance lines turn out to be purely in absorption and do not depend on both direction and distance to the burst center in contradistinction to the profiles in subordinate lines. The profiles contain jumps on frequencies corresponding to appearance of a source (burst) at a given redshift z=z0. For z0=5000 the jumps in hydrogen La and Lb lines are on frequencies 493 and 584 GHz respectively and jumps in two HeI lines are on 855 and 930 GHz for z0=6000. Relative magnitude of jumps amounts to 1e-4 - 3e-3.

astro-ph.CO↗
arXiv2016

Local bursts model of primordial CMB temperature fluctuations: scattering in hydrogen lines

Within the framework of a flat cosmological model a propagation of an instantaneous burst of isotropic radiation is considered from the moment of its beginning at some initial redshift z0 to the moment of its registration now (at z=0). Thomson scattering by free electrons and scattering in primordial hydrogen lines Ha, Hb, Pa and Pb are considered as the sources of opacity and when calculating an albedo of a single scattering in the lines we take into account deactivation of the upper levels of transitions by background blackbody radiation. Profiles for these lines in a burst spectrum are calculated for different distances from the center of the burst and different values of z0. In the first approximation these profiles do not depend on spectrum and intensity of a burst radiation. It is shown that lines are in absorption at sufficiently large distance but emission components may appear as a distance decreases and it becomes stronger while absorption component weakens with a further distance decrease. For the sum of Ha and Hb lines the depth of absorption can reach 2e-4 while for the sum of Pa and Pb lines the maximum absorption is about 7e-6. So that the relative magnitude of temperature fluctuations lies between 1e-7 and 1e-9. The calculations were fulfiled for bursts with different initial sizes. For the same z0 the profiles of hydrogen lines are practically coinside for burst sizes lower than someone and for greater ones the lines weaken as the burst size grows.

astro-ph.CO↗
arXiv2014

EIT phenomenon for the three-level hydrogen atoms and its application to the era of the cosmological recombination

The electromagnetically induced transparency (EIT) phenomenon in earlier universe is considered. We evaluated the elementary processes of the single scattering of photon on the hydrogen atom with the purpose of their use in the tasks of the radiation transfer theory. The additional function $f$, which depends on external conditions, is found. This function can be considered as an adjustment of the optical depth that leads to the necessity of modernization of the escape probability $p_{ij}(τ_S)\rightarrow p_{ij}(τ_S(1+f))$. The numerical values of $f$ for the different schemes of atom in three-level approximation are given. It is found that the magnitude of function $f$ could influence significantly on the formation of CMB in some partial cases.

physics.atom-ph↗
arXiv2013

Cosmological dinosaurs

The hypothesis of existence of primordial black holes with large masses (\geq 10^6 M\odot), formed at the earliest stages of the Universe evolution, is considered in the paper. The possibility does not contradict some theories, see e.g. Barkana & Loeb (2001), and may match new observational data. In particular, this scenario of evolution could describe some peculiarities in distant galaxies and quasars. Calculations of evolution of central body mass in protogalaxies for different initial conditions are presented. It is shown that the sufficient rate of BH mass growth is not achieved in the standard scheme without complex additional assumptions. Moreover, the appearance of a primordial black hole in the epoch of primordial nucleosynthesis could significantly change the chemical composition around it. This can lead to different exotic stars with low mass and nonstandart metals enrichment. The proposed scheme is not considered as universal. On the other hand, if only tiny part of existed objects have the considered nature, it gives a unique possibility to study extremal stages of matter and fields evolution in our Universe.

astro-ph.CO↗
arXiv2013

Is a single photon's wave front observable?

The ultimate goal and the theoretical limit of weak signal detection is the ability to detect a single photon against a noisy background. [...] In this paper we show, that a combination of a quantum metamaterial (QMM)-based sensor matrix and quantum non-demolition (QND) readout of its quantum state allows, in principle, to detect a single photon in several points, i.e., to observe its wave front. Actually, there are a few possible ways of doing this, with at least one within the reach of current experimental techniques for the microwave range. The ability to resolve the quantum-limited signal from a remote source against a much stronger local noise would bring significant advantages to such diverse fields of activity as, e.g., microwave astronomy and missile defence. The key components of the proposed method are 1) the entangling interaction of the incoming photon with the QMM sensor array, which produces the spatially correlated quantum state of the latter, and 2) the QND readout of the collective observable (e.g., total magnetic moment), which characterizes this quantum state. The effects of local noise (e.g., fluctuations affecting the elements of the matrix) will be suppressed relative to the signal from the spatially coherent field of (even) a single photon.

quant-ph↗
arXiv2012

Investigation of the electromagnetically induced transparency in era of cosmological hydrogen recombination

Investigation of the cosmic microwave background formation processes is one of the most actual problem at present time. In this paper we analyze the response of the hydrogen atom to the external photon fields. Field characteristics are defined via conditions corresponding to the recombination era of universe. Approximation of three-level atom is used to describe the "atom - fields" interaction. It is found that the phenomena of the electromagnetically induced transparancy takes place in this case. Consideration of EIT phenomena makes it necessary to update astrophysical description of the processes of the cosmic microwave background formation and, in particular, Sobolev escape probability. Additional terms to the optical depth in definition of Sobolev escape probability on the level about 1% are found.

physics.atom-ph↗
arXiv2010

Propagation of the burst of radiation in expanding and recombining Universe: Thomson scattering

Within the framework of a flat cosmological model a propagation of an instantaneous burst of nonpolarized isotropic radiation is considered from the moment of its beginning at some initial redshift z0 to the moment of its registration now (at z=0). Thomson (Rayleigh) scattering by free electrons is considered as the only source of opacity. Spatial distributions of the mean (over directions) radiation intensity are calculated as well as angular distributions of radiation intensity and polarization at some different distances from the center of the burst. It is shown that for redshifts z0 large enough (z0 > 1400) the profile of the mean intensity normalized to the total number of photons emitted during the burst weakly depends on initial conditions (say the moment z0 of the burst, the width and shape of initial radiation distribution in space). As regards angular distributions of intensity and polarization they turn to be rather narrow (3 - 5 arcmin) while polarization can reach 70%. On the average an expected polarization can be about 15%.

astro-ph.CO↗
arXiv2008

Dynamics of Primordial Hydrogen Recombination with Allowance for a Recoil for Scattering in the Ly-alpha Line

It is shown that taking into account a recoil for radiation scattering in the Ly-alpha line can lead to a noticable acceleration of primordial hydrogen recombination. Thus for LambdaCDM model a decrease of ionization degree exceeds 1% for redshifts z in a range 800 - 1050 achieving approximately 1.3% at z=900. Corresponding corrections to the cosmic microwave background power spectra can achieve 1.1% for TT spectra and 1.7% for EE ones. Radiative transfer in these calculations was treated in a quasistationary approximation. Numerical solutions are also obtained in diffusion approximation for a nonstationary problem of Ly-alpha line radiative transfer under partial frequency redistribution with a recoil. An evolution of a local line profile is traced to as well as an evolution of a relative number of uncompensated transitions from 2p state down to 1s one. It is shown that taking into account nonstationarity of Ly-alpha line radiative transfer can lead to an additional acceleration of primordial hydrogen recombination.

astro-ph↗
arXiv2005

Dynamics of the Primordial Hydrogen and Helium (HeI) Recombination in the Universe

The dependences on z of fractional number densities of H+ and He+ ions are calculated with a proper allowance for two-photon decays of upper levels of hydrogen and parahelium and radiative transfer in intercombination line 2 3P_1 --> 1 1S_0 of helium. It is shown that for hydrogen this gives corrections for a degree of ionization in no more than a few percents but for helium this leads to a significant acceleration of recombination compared to the recent papers by Seager et al. (1999; 2000) where these effects were ignored.

astro-ph↗
arXiv2003

Primordial bound systems of superheavy particles as the source of ultra-high energy cosmic rays

Annihilation of superheavy particles in primordial bound systems is considered as the source of Ultra High Energy Cosmic Rays (UHECR).Charge conservation makes them to be produced in pairs, and the estimated separation of particle and antiparticle in such pair is shown to be in some cases much smaller than the average separation determined by the averaged number density of considered particles. If the new U(1) charge is the source of a long range field similar to electromagnetic field, the particle and antiparticle, possessing that charge, can form primordial bound system with annihilation timescale, which can satisfy the conditions, assumed for this type of UHECR sources. These conditions severely constrain the possible properties of considered particles. So, the proposed mechanism of UHECR origin is impossible to realise, if the U(1) charged particles share ordinary weak, strong or electromagnetic interactions. It makes the proposed mechanism of pairing and binding of superheavy U(1) charged particles an effective theoretical tool in the probes of the physics of very early Universe and of the hidden sector of particle theory, underlying it.

hep-ph↗
arXiv2003

Primordial pairing and binding of superheavy charge particles in the early Universe

Primordial superheavy particles, considered as the source of Ultra High Energy Cosmic Rays (UHECR) and produced in local processes in the early Universe, should bear some strictly or approximately conserved charge to be sufficiently stable to survive to the present time. Charge conservation makes them to be produced in pairs, and the estimated separation of particle and antiparticle in such pair is shown to be in some cases much smaller than the average separation determined by the averaged number density of considered particles. If the new U(1) charge is the source of a long range field similar to electromagnetic field, the particle and antiparticle, possessing that charge, can form primordial bound system with annihilation timescale, which can satisfy the conditions, assumed for this type of UHECR sources. These conditions severely constrain the possible properties of considered particles.

astro-ph↗
arXiv2003

Polarization of cosmic microwave background scattered by moving flat protoobjects

The work is devoted to the investigations of possible observational manifestations of protoobjects related to "dark ages" epoch (10 < z < 1000), before formation of self-luminous galaxies and stars. These objects can distort the cosmic microwave background. Formation of these objects is described in the "pancake theory" and in the model of "hierarchic clustering". According to these theories we may consider these protoobjects as flat layers. We consider both Thomson (with Rayleigh phase matrix) and resonance (for complete frequency redistribution) scattering of cosmic microwave background radiation by moving flat layer. The appearing anisotropy and polarization of cosmic microwave radiation are calculated for a wide range of a layer optical thicknesses (from optically thin layer to optically thick one). Analytical solutions are also obtained for the case of an optically thin layer and are compared with the numerical ones.

astro-ph↗
arXiv2002

A differential method of search for the CMBR spectral-spatial fluctuations

The CMBR spectral-spatial fluctuations (SSF) formed in early Universe during the Dark Ages are considered. Main attention is focused on the narrow-band spectral properties of the SSF. Based on these properties we propose to use a differential method in order to search for these fluctuations. Description of the method is given.

astro-ph↗