Search

The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3~PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy $\gamma$-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte--Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a $\gamma$-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 hours of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations with $\mathcal{O}(100)$ hours of exposure per source., Comment: 34 pages, 16 figures, Accepted for publication in Astroparticle Physics

Evolution of cosmological perturbations is considered in the model with dynamical dark energy which non-gravitationally interacts with dark matter. The dark energy equation of state parameter (EoS) is varying in time and is parameterized by its adiabatic sound speed. Such model of interacting dark energy has advantages over model with constant EoS, because it avoids non-adiabatic instabilities of dark energy at radiation dominated epoch for certain types of interaction in dark sector. The stability conditions for solutions of equations of dark energy perturbations were derived. The impact of strength of additional interaction between dark components on the evolution of density and velocity perturbations in them is analysed for quintessence and phantom types of dark energy., Comment: 11 pages, 3 figures

We study the density distribution of the minimally-coupled scalar field dark energy inside a neutron star. The dark energy is considered in the hydrodynamical representation as a perfect fluid with three parameters (background density, equation of state, and effective sound speed). The neutron star matter is modeled with three unified equations of state, developed by the Brussels-Montreal group. With the calculated density distribution of the dark energy inside a neutron star (and its dependence on the dark energy parameters) we investigate how its presence impacts the macroscopic characteristics and the value of the mass limit for neutron stars. From this impact we derive the possible constrains on the effective speed of sound of dark energy with the help of maximal known masses of observed neutron stars. In this approach, we have found, that the squared effective speed of sound can not be smaller than $\sim 10^{-2}$ in units of squared speed of light.

The emission in the hyperfine structure 21 cm line of atomic hydrogen arising in the halos with masses $\sim10^6-10^{10}$ M$_\odot$ from the Dark Ages in the models with Warm Dark Matter (WDM) is analysed. The halos are assumed to be formed from Gaussian density peaks of cosmological density perturbations at $10\lesssim z\lesssim50$. Semi-analytical modelling of the formation of individual spherical halos in multi-component models shows that gas in them has the kinetic temperature in the range of $60-800$ K under adiabatic compression of the collapsing halo, and the temperature of each halo depends on the time of virialization. It is shown that inelastic collisions between neutral hydrogen atoms are the dominant excitation mechanism for hyperfine structure levels, which pulls the spin temperature closer to the kinetic temperature. The brightness temperature of individual halos is in the range of 1-10 K, depending on the mass of the halo and its virialization redshift, and increasing as these two increase. The apparent angular radii of such halos are in the range 0.06-1.2 arcseconds, their surface number density decreasing exponentially from a few per arcmin$^2$ for the lowest mass and redshift to nearly zero for higher values. Assuming a 1 MHz observation bandwidth the surface number density of the halo at various redshifts is evaluated as well as beam-averaged differential antenna temperatures and fluxes of hydrogen emission from halos of different masses. The beam-averaged signal strongly depends on the cut-off scale in the mass function of dark ages halos that may be caused by free-streaming of WDM particles. The finding is compared with the upper limits on the amplitude of the power spectrum of the hydrogen 21-cm line fluctuations derived from the recent observation data obtained with MWA and LOFAR., Comment: 18 pages, 10 figures, 7 tables; accepted for publication in Physics of the Dark Universe

We analyse the thermal emission and resonant scattering of CMB radiation from the dark ages halos in the rotational lines of the helium hydride ion (HeH$^{+}$), one of the first chemical compounds in the Universe. Evaluating the optical depth, thermal and resonant brightness temperatures and spectral fluxes of dark ages halos is based on computing the cross-sections and rate coefficients of excitation/de-excitation of the lowest five rotational states of HeH$^{+}$ by inelastic collisions with atomic hydrogen. It was shown that in the Dark Ages the collisional excitation/de-excitation by atoms of neutral hydrogen and electrons are competitive, whereas in the denser regions, e.g., in the halos, the contribution of collisions with atomic hydrogen is dominant. We demonstrate the peak-like time-dependence of halo luminosities in HeH$^{+}$ lines., Comment: 13 pages, 9 figures, 9 tables; accepted for publication in Phys.Rev.D

The emission from dark ages halos in the lines of transitions between lowest rotational levels of hydrogen and hydrogen deuteride molecules is analyzed. It is assumed molecules to be excited by CMB and collisions with hydrogen atoms. The physical parameters of halos and number density of molecules are precalculated in assumption that halos are homogeneous top-hat spheres formed from the cosmological density perturbations in the four-component Universe with post-Planck cosmological parameters. The differential brightness temperatures and differential spectral fluxes in the rotational lines of H$_2$-HD molecules are computed for two phenomena: thermal luminescence and resonant scattering of CMB radiation. The results show that expected maximal values of differential brightness temperature of warm halos ($T_K\sim$200-800 K) are at the level of nanokelvins, are comparable for both phenomena, and are below sensitivity of modern sub-millimeter radio telescopes. For hot halos ($T_K\sim$2000-5000 K) the thermal emission of H2-ortho molecules dominates and the differential brightness temperatures are predicted to be of a few microkelvins at the frequencies 300-600 GHz, that could be detectable with telescopes of a new generation., Comment: 18 pages, 9 figures, 16 tables; accepted for publication in ApJ; in the revised version the discussion about impact of new coefficients of collision excitation H2-H on the brightness temperature as well as the comparison with results of other authors are added

We study the formation of first molecules, negative Hydrogen ions and molecular ions in model of the Universe with cosmological constant and cold dark matter. The cosmological recombination is described in the framework of modified model of the effective 3-level atom, while the kinetics of chemical reactions in the framework of the minimal model for Hydrogen, Deuterium and Helium. It is found that the uncertainties of molecular abundances caused by the inaccuracies of computation of cosmological recombination are about 2-3%. The uncertainties of values of cosmological parameters affect the abundances of molecules, negative Hydrogen ions and molecular ions at the level of up to 2%. In the absence of cosmological reionization at redshift $z=10$ the ratios of abundances to the Hydrogen one are $3.08\times10^{-13}$ for $H^-$, $2.37\times10^{-6}$ for $H_2$, $1.26\times10^{-13}$ for $H_2^+$, $1.12\times10^{-9}$ for $HD$ and $8.54\times10^{-14}$ for $HeH^+$., Comment: 12 pages, 1 figure, 3 tables

We study the dynamics of expansion of the homogeneous isotropic Universe and the evolution of its components in the model with nonminimally coupled dynamical dark energy. Dark energy, like the other components of the Universe, is described by the perfect fluid approximation with the equation of state (EoS) $p_ {de}=w\rho_{de}$, where the EoS parameter $w$ depends on time and is parameterized via the squared adiabatic sound speed $c_{ a}^2$ which is assumed to be constant. On basis of the general covariant conservation equations for the interacting dark energy and dark matter and Einstein equations in Friedmann-Lemaitre-Robertson-Walker metric we analyze the evolution of energy densities of the hidden components and the dynamics of expansion of the Universe with two types of interaction: proportional to the sum of densities of the hidden components and proportional to their product. For the first interaction the analytical expressions for the densities of dark energy and dark matter were obtained and analyzed in detail. For the second one the evolution of densities of hidden components of the Universe was analyzed on basis of the numerical solutions of their energy-momentum conservation equations. For certain values of the parameters of these models the energy densities of dark components become negative. So to ensure that the densities are always positive we put constraints on the interaction parameter for both models., Comment: 7 pages, 4 figures

The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document., Comment: 213 pages, including references and glossary. Version 2: credits and references updated, some figures updated, and author list updated

List of contributions from the Cherenkov Telescope Array Consortium presented at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea., Comment: Index of Cherenkov Telescope Array conference proceedings at the ICRC2017, Busan, Korea

The galaxy data provided by COSMOS survey for 1 by 1 degree field of sky are analysed by methods of complex networks. Three galaxy samples (slices) with redshifts ranging within intervals 0.88-0.91, 0.91-0.94 and 0.94-0.97 are studied as two-dimensional projections for the spatial distributions of galaxies. We construct networks and calculate network measures for each sample, in order to analyse the network similarity of different samples, distinguish various topological environments, and find associations between galaxy properties (colour index and stellar mass) and their topological environments. Results indicate a high level of similarity between geometry and topology for different galaxy samples and no clear evidence of evolutionary trends in network measures. The distribution of local clustering coefficient C manifests three modes which allow for discrimination between stand-alone singlets and dumbbells (0 <= C <= 0.1), intermediately (0 < C < 0.9) and clique (0.9 <= C <= 1) like galaxies. Analysing astrophysical properties of galaxies (colour index and stellar masses), we show that distributions are similar in all slices, however weak evolutionary trends can also be seen across redshift slices. To specify different topological environments we have extracted selections of galaxies from each sample according to different modes of C distribution. We have found statistically significant associations between evolutionary parameters of galaxies and selections of C: the distribution of stellar mass for galaxies with interim C differ from the corresponding distributions for stand-alone and clique galaxies, and this difference holds for all redshift slices. The colour index realises somewhat different behaviour., Comment: 12 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX~J1713.7$-$3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very-high-energy (VHE) gamma rays. Special attention is paid to explore possible spatial (anti-)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H{\sc i} emission. We present a series of simulated images of RX J1713.7$-$3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the non-thermal X-ray emission observed by {\it XMM-Newton}, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H{\sc i} observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic vs leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator., Comment: 19 pages, 5 figures. Accepted for publication in ApJ

The formation of large voids in the Cosmic Web from the initial adiabatic cosmological perturbations of space-time metric, density and velocity of matter is investigated in cosmological model with the dynamical dark energy accelerating expansion of the Universe. It is shown that the negative density perturbations with the initial radius of about 50 Mpc in comoving to the cosmological background coordinates and the amplitude corresponding to the r.m.s. temperature fluctuations of the cosmic microwave background lead to the formation of voids with the density contrast up to $-$0.9, maximal peculiar velocity about 400 km/s and the radius close to the initial one. An important feature of voids formation from the analyzed initial amplitudes and profiles is establishing the surrounding overdensity shell. We have shown that the ratio of the peculiar velocity in units of the Hubble flow to the density contrast in the central part of a void does not depend or weakly depends on the distance from the center of the void. It is also shown that this ratio is sensitive to the values of dark energy parameters and can be used to find them based on the observational data on mass density and peculiar velocities of galaxies in the voids., Comment: 10 pages, 3 figures

List of contributions from the Cherenkov Telescope Array (CTA) Consortium presented at the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016), July 11-15, 2016, in Heidelberg, Germany., Comment: Index of CTA conference proceedings for the Gamma 2016, Heidelberg, Germany

We consider the dark energy model with barotropic equation of state, which interacts with dark matter through gravitation and another force, causing the energy-momentum exchange between them. Both components are described in approximation of ideal fluids, which are parametrized by density and equation of state parameters. Three types of interactions between dark components are considered: the interaction independent from their densities, the one proportional to density of dark energy and the one proportional to density of dark matter. The equations which describe the expansion dynamics of homogeneous and isotropic Universe and evolution of densities of both components for different values of interaction parameter are obtained on the bases of the general covariant conservation equations and Einstein's ones. For three kinds of interactions we show the existence of the range of values of parameters of dark energy for which the densities of dark components and their sum are negative. We find the conditions of positivity of density of dark energy and dark matter. The constraints on the value of parameter of interaction are derived. The dynamics of expansion of the Universe with these interactions of dark energy and dark matter is analysed., Comment: 18 pages, 6 figures, published in Kinematics and Physics of Celestial Bodies (2016)

We investigate the non-linear evolution of spherical density and velocity perturbations of dark matter and dark energy in the expanding Universe. For that we have used the conservation and Einstein equations to describe the evolution of gravitationally coupled inhomogeneities of dark matter, dark energy and radiation from linear stage in the early Universe to the non-linear one at the current epoch. The simple method of the numerical integration of the system of non-linear differential equations for evolution of the central part of halo is proposed. The results are presented for halo of cluster ($k=2$ Mpc$^{-1}$) and supercluster scales ($k=0.2$ Mpc$^{-1}$) and show that quintessential scalar field dark energy with small value of effective speed of sound $c_s<0.1$ can give noticeable impact on the formation of large scale structures in the expanding Universe., Comment: 6 pages, 6 figures; accepted by Advances in Astronomy and Space Physics

The book elucidates the current state of the dark energy problem and presents the results of the authors, who work in this area. It describes the observational evidence for the existence of dark energy, the methods and results of constraining of its parameters, modeling of dark energy by scalar fields, the space-times with extra spatial dimensions, especially Kaluza---Klein models, the braneworld models with a single extra dimension as well as the problems of positive definition of gravitational energy in General Relativity, energy conditions and consequences of their violation in the presence of dark energy. This monograph is intended for science professionals, educators and graduate students, specializing in general relativity, cosmology, field theory and particle physics., Comment: Book, 380 p., 88 figs., 7 tables; 1st volume of three-volume book "Dark energy and dark matter in the Universe", ed. V. Shulga, Kyiv, Academperiodyka, 2013; ISBN 978-966-360-239-4, ISBN 978-966-360-240-0 (vol. 1). arXiv admin note: text overlap with arXiv:0706.0033, arXiv:1104.3029 by other authors

The distribution of dark energy density in the vicinity of compact static objects is analyzed. Dark energy is assumed to be in the form of a scalar field with three parameters: the background density, the equation of state parameter and the effective sound speed. Compact object is assumed to be a homogeneous spherical object of constant radius. We use the solutions of the hydrodynamical equations for dark energy in the gravitational fields of such objects for cases of static distribution of dark energy in the vicinity of star and stationary accretion onto black hole in order to analyze the possibility of constraining of the parameters of dark energy from astrophysical data. We show that dependence of density of dark energy in the vicinity of such object on the effective sound speed, background density and equation of state parameter of dark energy makes it possible to try such tests. Here we exploit the accuracy of determination of masses of Sun and black hole in the center of Milky Way to obtain the lower limit on the effective sound speed of dark energy., Comment: 5 pages, 2 figures; WDS'14 Proceedings of Contributed Papers

We study the dynamical properties and space distribution of dark energy in the weak and strong gravitational fields caused by inhomogeneities of matter in the static world of galaxies and clusters. We show that the dark energy in the weak gravitational fields of matter density perturbations can condense or dilute, but amplitudes of its perturbations remain very small on all scales. We illustrate also how the "accretion" of the phantom dark energy onto the matter overdensity forms the dark energy underdensity. We analyze the behavior of dark energy in the gravitational fields of stars and black holes with the Schwarzschild metric. It is shown that, in the case of stars, the static solution of the differential equations for energy-momentum conservation exists and describes the distribution of density of dark energy inside and outside of a star. We have found that for stars and galaxies its value differs slightly from the average and is a bit higher for the quintessential scalar field as dark energy and a bit lower for the phantom one. The difference grows with the decrease of the effective sound speed of dark energy and is large in the neighborhood of neutron stars. We obtain and analyze also the solutions of equations that describe the stationary accretion of the dark energy as a test component onto the Schwarzschild black hole. It is shown that the rate of change of mass of the dark energy is positive in the case of quintessential dark energy and is negative in the case of the phantom one., Comment: 13 pages, 4 figures, 1 table; v2: text corrected and supplemented; v3: corrected to the version accepted for publication in Phys. Rev. D

We determine the best-fit values and confidence limits for dynamical dark energy parameters together with other cosmological parameters on the basis of different datasets which include WMAP9 or Planck-2013 results on CMB anisotropy, BAO distance ratios from recent galaxy surveys, magnitude-redshift relations for distant SNe Ia from SNLS3 and Union2.1 samples and the HST determination of the Hubble constant. We use a Markov Chain Monte Carlo routine to map out the likelihood in the multi-dimensional parameter space. We show that the most precise determination of cosmological parameters with the narrowest confidence limits is obtained for the Planck{+}HST{+}BAO{+}SNLS3 dataset. The best-fit values and 2$\sigma$ confidence limits for cosmological parameters in this case are $\Omega_{de}=0.718\pm0.022$, $w_0=-1.15^{+0.14}_{-0.16}$, $c_a^2=-1.15^{+0.02}_{-0.46}$, $\Omega_bh^2=0.0220\pm0.0005$, $\Omega_{cdm}h^2=0.121\pm0.004$, $h=0.713\pm0.027$, $n_s=0.958^{+0.014}_{-0.010}$, $A_s=(2.215^{+0.093}_{-0.101})\cdot10^{-9}$, $\tau_{rei}=0.093^{+0.022}_{-0.028}$. For this dataset, the $\Lambda$CDM model is just outside the 2$\sigma$ confidence region, while for the dataset WMAP9{+}HST{+}BAO{+}SNLS3 the $\Lambda$CDM model is only 1$\sigma$ away from the best fit. The tension in the determination of some cosmological parameters on the basis of two CMB datasets WMAP9 and Planck-2013 is highlighted., Comment: 16 pages, 5 figures, 2 tables; accepted for publication in JCAP

The Workshop on results of the Project Kosmomikrofizyka-2 (Astroparticle Physics) of the National Academy of Sciences (NAS) of Ukraine "Astrophysical and cosmological problems of invisible mass and dark energy in the Universe" was held on November 21-22, 2012 in the Institute for Nuclear Research, Kyiv, Ukraine (http://lpd.kinr.kiev.ua/kmf12). This Project was carried out during three years (2010-2012) by scientists from various universities and institutes of the National Academy of Sciences of Ukraine; it was a logical continuation of the previous scientific program of the NAS of Ukraine "Researches of structure and composition of the Universe, hidden mass and dark energy (Kosmomikrofizyka)" in 2007-2009. These programs were devoted to theoretical and experimental investigations in astronomy, astrophysics, cosmology, physics of atomic nuclei and particle physics, which are related with the problems of dark matter and dark energy in the Universe., Comment: Proceedings of the Workshop on results of the Project Kosmomikrofizyka-2 (Astroparticle Physics) of the National Academy of Sciences of Ukraine, November 21-22, 2012, Institute for Nuclear Research, Kyiv, Ukraine. 94 pages, 29 figures, 5 tables (in English, Ukrainian, Russian)

We analyze the possibility to distinguish between quintessence and phantom scalar field models of dark energy using observations of luminosity distance moduli of SNe Ia, CMB anisotropies and polarization, matter density perturbations and baryon acoustic oscillations. Among the present observations only Planck data on CMB anisotropy and SDSS DR9 data on baryon acoustic oscillations may be able to decide between quintessence or phantom scalar field models, however for each model a set of best-fit parameters exists, which matches all data with similar goodness of fit. We compare the relative differences of best-fit model predictions with observational uncertainties for each type of data and we show that the accuracy of SNe Ia luminosity distance data is far from the one necessary to distinguish these types of dark energy models, while the CMB data (WMAP, ACT, SPT and especially Planck) are close to being able to reliably distinguish them. Also an improvement of the large-scale structure data (future releses of SDSS BOSS and e.g. Euclid or BigBOSS) will enable us to surely decide between quintessence and phantom dark energy., Comment: 16 pages, 8 figures, 2 tables, accepted for publication in JCAP

The possibility of constraining the parameters of scalar field dark energy with barotropic equation of state using different available datasets is discussed. It has been found that the initial value of dark energy equation of state parameter is constrained very weakly by most of the data. We have determined the constraints on this parameter, which come from the combined dataset including supernovae from the full SDSS compilation with the MLCS2k2 fitting of light curves. We discuss also the possibility of distinguishing between different dark energy models with barotropic equation of state using the future data on CMB anisotropies., Comment: 9 pages, 3 figures, 1 table; to appear in Proceedings of the 10th International Gamow Summer School, Section Cosmomicrophysics, Cosmology and Gravitation

The dynamics of expansion and large scale structure formation in the multicomponent Universe with dark energy modeled by the minimally coupled scalar field with generalized linear barotropic equation of state (EoS) are analyzed. It is shown that the past dynamics of expansion and future of the Universe -- eternal accelerated expansion or turnaround and collapse -- are completely defined by the current energy density of a scalar field and relation between its current and early EoS parameters. The clustering properties of such models of dark energy and their imprints in the power spectrum of matter density perturbations depend on the same relation and, additionally, on the "effective sound speed" of a scalar field, defined by its Lagrangian. It is concluded that such scalar fields with different values of these parameters are distinguishable in principle. This gives the possibility to constrain them by confronting the theoretical predictions with the corresponding observational data. For that we have used the 7-year WMAP data on CMB anisotropies, the Union2 dataset on Supernovae Ia and SDSS DR7 data on luminous red galaxies (LRG) space distribution. Using the Markov Chain Monte Carlo technique the marginalized posterior and mean likelihood distributions are computed for the scalar fields with two different Lagrangians: Klein-Gordon and Dirac-Born-Infeld ones. The properties of such scalar field models of dark energy with best fitting parameters and uncertainties of their determination are also analyzed in the paper., Comment: 17 pages, 9 figures, 2 tables, minor corrections, references added, accepted for publication in Phys. Rev. D

We analyse the redshift dependence of space number density of quasars assuming that they are the short-lived active stages of the massive galaxies and arise immediately after the collapse of homogeneous central part of protogalaxy clouds. Obtained dependence fits the observational data ChaMP+CDF+ROSAT (Silverman et al. 2005) very well for protogalaxy clouds of mass $M\approx 8\cdot 10^{11}$ $h^{-1}M_{\odot}$ and ellipticity $e<0.4$. The lifetime of bright X-ray AGNs or QSOs with $L_X>10^{44.5}$ erg$\cdot s^{-1}$ in the range of energies $0.3-8$ keV is $\tau_{QSO}\sim 6\cdot10^6$ years when the mass of supermassive black hole is $M_{SMBH}\sim 10^{9}$ $M_{\odot}$ and the values of other quasar parameters are reasonable. The analysis and all calculations were carried out in the framework of $\Lambda$CDM-model with parameters determined from 5-years WMAP, SNIa and large scale structure data (Komatsu et al. 2009). It is concluded, that the halo model of galaxy formation in the $\Lambda$CDM cosmological model matches well observational data on AGNs and QSOs number density coming from current optical and X-ray surveys., Comment: 8 pages, 1 figure; published in J. Phys. Studies, v. 14, No. 2, p. 2901-1 (2010); http://www.ktf.franko.lviv.ua/JPS/index_ua.html

The power spectrum of number density perturbations of free electrons is obtained for the epoch of cosmological recombination of hydrogen. It is shown that amplitude of the electron perturbations power spectrum of scales larger than acoustic horizon exceeds by factor of 17 the amplitude of baryon matter density ones (atoms and ions of hydrogen and helium). In the range of the first and second acoustic peaks such relation is 18, in the range of the third one 16. The dependence of such relations on cosmological parameters is analysed too., Comment: 16 pages, 4 figures, 2 tables

The evolution of scalar perturbations is studied for 2-component (non-relativistic matter and dark energy) cosmological models at the linear and non-linear stages. The dark energy is assumed to be the scalar field with either classical or tachyonic Lagrangian and constant equation-of-state parameter w. The fields and potentials were reconstructed for the set of cosmological parameters derived from observations. The comparison of the calculated within these models and experimental large-scale structure characteristics is made. It is shown that for w=const such analysis can't remove the existing degeneracy of the dark energy models., Comment: 15 pages, 5 figures, text corrected, references added, accepted by Kinematics and Physics of Celestial Bodies

The dynamics of expansion of the Universe and evolution of scalar perturbations are studied for the quintessential scalar fields $Q$ with the classical Lagrangian satisfying the additional condition $w=const$ or $c^2_a=0$. Both quintessential fields are studied for the same cosmological model. The systems of evolutionary equations for gauge-invariant perturbations of metrics, matter and quintessence have been analysed analyticaly for the early stage of the Universe life and numerically up to the present epoch. It is shown that amplitudes of the adiabatic matter density perturbations grow like in $\Lambda$CDM-model but time dependences of amplitudes of the quintessence perturbations are more varied: gauge-invariant variables $D_g^{(Q)}$ and $D_s^{(Q)}$ decay from initial constant value after entering the particle horizon while $D^{(Q)}$ and $V^{(Q)}$ grow at the early stage before entering the horizon and decay after that -- in the quintessence-dominated epoch, when gravitational potential starts to decay -- so, that at the current epoch they are approximately two orders lower than matter ones at the supercluster scale. Therefore, at the subhorizon scales the quintessential scalar fields are smoothed out while the matter clusters. It is also shown that both quintessential scalar fields suppress the growth of matter density perturbations and the amplitude of gravitational potential. In these QCDM-models -- unlike $\Lambda$CDM ones -- such suppression is scale dependent and more visible for the quintessence with $c^2_a=0$., Comment: 12 pages, 6 figures, typos corrected

The features of a homogeneous scalar field $\phi$ with classical Lagrangian $L=\phi_{;i}\phi^{;i}/2-V(\phi)$ and tachyon field Lagrangian $L=-V(\phi)\sqrt{1-\phi_{;i}\phi^{;i}}$ causing the observable accelerated expansion of the Universe are analyzed. The models with constant equation-of-state parameter $w_{de}=p_{de}/\rho_{de}<-1/3$ are studied. For both cases the fields $\phi(a)$ and potentials $V(a)$ are reconstucted for the parameters of cosmological model of the Universe derived from the observations. The effect of rolling down of the potential $V(\phi)$ to minimum is shown., Comment: 14 pages, 14 figures, accepted for publication by Kinematics and Physics of Celestial Bodies (UA)

The parameters of cosmological model with cold dark matter and cosmological constant (Lambda CDM) have been determined on a basis of three-year cosmic microwave background observations by space mission WMAP, as well as the data on the large-scale structure of the Universe. The data cover scales from 1 up to 10000 Mpc. The best-fit values of LambdaCDM model parameters were found by minimization of chi^2 using the Levenberg-Markquardt approach (Omega_Lambda=0.736+-0.065, Omega_m=0.238+-0.080, Omega_b=0.05+-0.011, h=0.68+- 0.09, sigma_8=0.73+-0.08 and n_s=0.96+-0.015). It is shown that the LambdaCDM model with these values of the parameters agrees well with the angular power spectrum of cosmic microwave background and with power spectra of the density perturbations, estimated from spatial distributions of galaxies, rich galaxy clusters and from statistics of Ly_alpha absorption lines in spectra of distant quasars as well. The accordance of modeled characteristics of the large-scale structure with observable ones was analyzed, and possible reasons of significant discrepancies between some of them were considered., Comment: 12 pages, 6 figures, translation from Ukrainian

A development of perturbations of number densities of ions and electrons during recombination epoch is analysed. The equations for relative perturbations of ionization fractions were derived from the system of equations for accurate computation of the ionization history of the early Universe given by Seager et al. (1999,2000). It is shown that strong dependence of ionization and recombination rates on the density and temperature of plasma provides the significant deviations of amplitudes of ionization fractions relative perturbations from ones of baryon matter density adiabatic perturbations. Such deviations are most prominent for cosmological adiabatic perturbations of scales larger than sound horizon at recombination epoch. The amplitudes of relative perturbations of number densities of electrons and protons at last scattering surface exceed by factor of $\simeq$5 the amplitude of relative perturbation of baryons total number density, for helium ions this ratio reaches the value of $\simeq$18. For subhorizon cosmological perturbations these ratios appear to be essentially lesser and depend on oscillation phase at the moment of decoupling. These perturbations of number densities of ions and electrons at recombination epoch do not contribute to the intrinsic plasma temperature fluctuations but cause the ''corrugation'' of last scattering surface in optical depth, $\delta z_{dec}/(z_{dec}+1)\approx -\delta_b/3$, at scales larger than sound horizon. It may result into noticeable changes of precalculated values of CMB polarization pattern at several degrees angular scales., Comment: Accepted for publication in MNRAS; 13 pages, 4 figures, 1 table; used code is made available; referee recommendations are included; minor changes in the text and figures

We studied the WMAP temperature anisotropy data using two different methods. The derived signal gradient maps show regions with low mean gradients in structures near the ecliptic poles and higher gradient values in the wide ecliptic equatorial zone, being the result of non-uniform observational time sky coverage. We show that the distinct observational time pattern present in the raw (cleaned) data leaves also its imprints on the composite CMB maps. Next, studying distribution of the signal dispersion we show that the north-south asymmetry of the WMAP signal diminishes with galactic altitude, confirming the earlier conclusions that it possibly reveals galactic foreground effects. As based on these results, one can suspect that the instrumental noise sky distribution and non-removed foregrounds can have affected some of the analyses of the CMB signal. We show that actually the different characteristic axes of the CMB sky distribution derived by numerous authors are preferentially oriented towards some distinguished regions on the sky, defined by the observational time pattern and the galactic plane orientation., Comment: 7 pages, 5 color figures, submitted to MNRAS; v2 Fig1a fixed (was the same as Fig2a)

The evolution of matter density perturbations in two-component model of the Universe consisting of dark energy (DE) and dust-like matter (M) is considered. We have analyzed it for two kinds of DE with $\omega\ne -1$: a) unperturbed energy density and b) perturbed one (uncoupled with matter). For these cases the linear equations for evolution of the gauge-invariant amplitudes of matter density perturbations are presented. It is shown that in the case of unperturbed energy density of DE the amplitude of matter density perturbations grow slightly faster than in the second case., Comment: 4 pages, 1 figure, submitted to the proceedings of international conference "Astronomy in Ukraine - Past, Present, Future", July 15-17, Kiev, Ukraine

We carry out the determination of the amplitude of relic gravitational waves power spectrum. Indirect best-fit technique was applied to compare observational data and theory predictions. As observations we have used data on large-scale structure (LSS) of the Universe and anisotropy of cosmic microwave background (CMB) temperature. The conventional inflationary model with 11 parameters has been investigated, all of them evaluated jointly. This approach gave us a possibility to find parameters of power spectrum of gravitational waves along with statistical errors. The main result consists in following: WMAP data on power spectrum of CMB temperature fluctuations along with LSS data prefer model with small amplitude of tensor mode power spectrum, close to zero. The upper limit for its amplitude at quadupole harmonics T/S=0.6 at 95% C.L., Comment: Submitted to the proceedings of international conference "Astronomy in Ukraine - Past, Present, Future", July 15-17, Kiev, Ukraine

We have analyzed the dependences of the threshold value of amplitude of linear density fluctuation collapsed at the current epoch, $\delta_c$, and its overdensity after virialization, $\Delta_c$, on matter density content, 3D curvature parameter and cosmological constant. Though the range for the threshold values of perturbation amplitude is quite narrow - $1.55\le \delta_c\le 1.75$ in the region of parameters $-0.4\le\Omega_k\le0.4$, $0\le\Omega_{\Lambda}\le 1$, $0.1\le\Omega_m\le 1$, the difference in the concentrations of rich clusters of galaxies (calculated within the Press-Schechter formalism framework) with real and with canonical values of $\delta_c$ reaches, and for some models exceeds, 30%. The range of changes for the overdensity after virialization, $\Delta_c$, is considerably wider for the same region of parameters: $60\le\Delta_c\le180$. It results into difference up to $\sim40$% between the X-ray temperatures of gas, as calculated for these values and for the canonical value of $\Delta_c=178$. Also we have found analytical approximations of the dependences $\delta_c(\Omega_m,\Omega_{\Lambda})$ and $\Delta_c(\Omega_m,\Omega_{\Lambda})$ with their accuracies for above mentioned region of parameters being no worse than 0.2% and 1.7% respectively., Comment: 17 pages, 8 figures, LaTeX (Accepted for publication by Journal of Physical Studies, 2003, No1)

The locations and amplitudes of three acoustic peaks and two dips in the last releases of the Boomerang, MAXIMA and DASI measurements of the cosmic microwave background (CMB) anisotropy power spectra as well as their statistical confidence levels are determined in a model-independent way. It is shown that the Boomerang-2001 data (Netterfield et al. 2001) fixes the location and amplitude of the first acoustic peak at more than 3\sigma confidence level. The next two peaks and dips are determined at a confidence level above 1\sigma but below 2\sigma. The locations and amplitudes of the first three peaks and two dips are 212+/-17, 5426+/-1218\mu K^2, 544+/-56, 2266+/-607\mu K^2, 843+/-35, 2077+/-876\mu K^2, 413+/-50, 1960+/-503\mu K^2, 746+/-89, 1605+/-650\mu K^2 respectively (1\sigma errors include statistical and systematic errors). The MAXIMA and DASI experiments give similar values for the extrema which they determine. The determined cosmological parameters from the CMB acoustic extrema data show good agreement with other determinations, especially with the baryon content as deduced from standard nucleosynthesis constraints. These data supplemented by the constraints from direct measurements of some cosmological parameters and data on large scale structure lead to a best-fit model which agrees with practically all the used experimental data within 1\sigma. The best-fit parameters are: \Omega_{\Lambda}=0.64^{+0.14}_{-0.27}, \Omega_{m}= 0.36^{+0.21}_{-0.11}, \Omega_b=0.047^{+0.093}_{-0.024}, n_s=1.0^{+0.59}_{-0.17}, h=0.65^{+0.35}_{-0.27} and \tau_c=0.15^{+0.95}_{-0.15} (plus/minus values show 1\sigma upper/lower limits obtained by marginalization over all other model parameters). The best-fit values of \Omega_{\nu} and T/S are close to zero, their 1\sigma upper limits are 0.17 and 1.7 respectively., Comment: 34 pages, 10 figures; accepted by ApJ; some corrections in the text are made and a few references are added

Observational data on the large scale structure (LSS) of the Universe are used to establish an upper limit for the amplitude of the tensor mode marginalized over all other cosmological parameters within the class of adiabatic inflationary models. It is shown that the upper 1$\sigma$ limit for the contribution of a tensor mode to the COBE DMR data is T/S$<1$., Comment: 3 pages, to appear in the proceedings of the IAU Symposium 201, Manchester, 7-11 August 2000

The observational data on the large scale structure (LSS) of the Universe are used to establish the upper limit on the neutrino content marginalized over all other cosmological parameters within the class of adiabatic inflationary models. It is shown that the upper 2$\sigma$ limit on the neutrino content can be expressed in the form $\Omega_{\nu}h^2/N_{\nu}^{0.64}\le0.042$ or, via the neutrino mass, $m_{\nu}\le4.0$eV., Comment: 5 pages, to appear in the proceedings of the CAPP2000 Conference, Verbier, Switzerland, July, 2000

The observational data on the large scale structure (LSS) of the Universe are used to determine cosmological parameters within the class of adiabatic inflationary models. We show that a mixed dark matter model with cosmological constant ($\Lambda$MDM model) and parameters $\Omega_m=0.37^{+0.25}_{-0.15}$, $\Omega_{\Lambda}=0.69^{+0.15}_{-0.20}$, $\Omega_{\nu}=0.03^{+0.07}_{-0.03}$, $N_{\nu}=1$, $\Omega_b=0.037^{+0.033}_{-0.018}$, $n_s=1.02^{+0.09}_{-0.10}$, $h=0.71^{+0.22}_{-0.19}$, $b_{cl}=2.4^{+0.7}_{-0.7}$ (1$\sigma$ confidence limits) matches observational data on LSS, the nucleosynthesis constraint, direct measurements of the Hubble constant, the high redshift supernova type Ia results and the recent measurements of the location and amplitude of the first acoustic peak in the CMB anisotropy power spectrum. The best model is $\Lambda$ dominated (65% of the total energy density) and has slightly positive curvature, $\Omega=1.06$. The clustered matter consists in 8% massive neutrinos, 10% baryons and 82% cold dark matter (CDM). It is shown that the LSS observations together with the Boomerang (+MAXIMA-1) data on the first acoustic peak rule out zero-$\Lambda$ models at more than $2\sigma$ confidence level., Comment: 5 pages (Proceedings of International Conference "Astronomy In Ukraine - 2000 And Beyond", Kyiv, Ukraine, 5-8 June 2000; to be published in Supplement Series of the "Kinematics and Physics of Celestial Bodies")

We use observational data on the large scale structure (LSS) of the Universe measured over a wide range of scales from sub-galactic up to horizon scale and on the cosmic microwave background anisotropies to determine cosmological parameters within the class of adiabatic inflationary models. We show that a mixed dark matter model with cosmological constant ($\Lambda$MDM model) and parameters $\Omega_m=0.37^{+0.25}_{-0.15}$, $\Omega_{\Lambda}=0.69^{+0.15}_{-0.20}$, $\Omega_{\nu}=0.03^{+0.07}_{-0.03}$, $N_{\nu}=1$, $\Omega_b=0.037^{+0.033}_{-0.018}$, $n_s=1.02^{+0.09}_{-0.10}$, $h=0.71^{+0.22}_{-0.19}$, $b_{cl}=2.4^{+0.7}_{-0.7}$ (1$\sigma$ confidence limits) matches observational data on LSS, the nucleosynthesis constraint, direct measurements of Hubble constant, the high redshift supernova type Ia results and the recent measurements of the location and amplitude of the first acoustic peak in the CMB anisotropy power spectrum. The best model is $\Lambda$ dominated (65% of the total energy density) and has slightly positive curvature, $\Omega=1.06$. The clustered matter consists in 8% massive neutrinos, 10% baryons and 82% cold dark matter (CDM). The upper 2$\sigma$ limit on the neutrino content can be expressed in the form $\Omega_{\nu}h^2/N_{\nu}^{0.64}\le0.042$ or, via the neutrino mass, $m_{\nu}\le4.0$eV. The upper 1(2)$\sigma$ limit for the contribution of a tensor mode to the COBE DMR data is T/S$<1(1.5)$. Furthermore, it is shown that the LSS observations together with the Boomerang (+MAXIMA-1) data on the first acoustic peak rule out zero-$\Lambda$ models at more than $2\sigma$ confidence limit., Comment: 13 pages, 3 figures; accepted by MNRAS; minor corrections in the text, a few references are added

The possibility of determining cosmological parameters on the basis of a wide set of observational data including the Abell-ACO cluster power spectrum and mass function, peculiar velocities of galaxies, the distribution of Ly-$\alpha$ clouds and CMB temperature fluctuations is analyzed. Using a $\chi^2$ minimization method, assuming $\Omega_{\Lambda}+\Omega_m =1$ and no contribution from gravity waves, we found that a tilted $\Lambda$MDM model with one sort of massive neutrinos and the parameters $n\approx 1.12$, $\Omega_m\approx 0.4$ ($\Omega_{\Lambda}\approx 0.6$), $\Omega_{cdm}\approx 0.3$, $\Omega_{\nu}\approx 0.06$, $\Omega_b\approx 0.04$ and $h\approx 0.7$ matches observational data best. $\Omega_{\nu}$ is higher for more species of massive neutrinos, $\sim 0.1$ for two and $\sim 0.13$ for three species. $\Omega_m$ raises by $\sim 0.08$ and $\sim 0.15$ respectively. Varying only a subset of parameters and fixing the others shows also that the observational data set used here rules out pure CDM models with $h\ge 0.5$, scale invariant primordial power spectrum, zero cosmological constant and spatial curvature at a very high confidence level, $>99.99%$. The corresponding class of MDM models are ruled out at $\sim 95%$ C.L. It is notable also that this data set determines the amplitude of scalar fluctuations approximately at the same level as COBE four-year data. It indicates that a possible tensor component in the COBE data cannot be very substantial., Comment: 9 pages, 1 figures (Proceedings of IV International Conference "Cosmology. Relativistic Astrophysics. Cosmoparticle Physics", Moscow, 17-24 October 1999; to be published in "Gravitation & Cosmology, Vol. 5 (1999), Supplement)

The possibility of determining cosmological parameters on the basis of a wide set of observational data including the Abell-ACO cluster power spectrum and mass function, peculiar velocities of galaxies, the distribution of Ly-$\alpha$ clouds and CMB temperature fluctuations is analyzed. Using a $\chi^2$ minimization method, assuming $\Omega_{\Lambda}+\Omega_{\rm{matter}} =1 $ and no contribution from gravity waves, we found that a tilted $\Lambda$MDM model with one sort of massive neutrinos and the parameters $n=1.12\pm 0.10$, $\Omega_m=0.41\pm 0.11$ ($\Omega_{\Lambda}=0.59\pm0.11$), $\Omega_{cdm}=0.31\pm 0.15$, $\Omega_{\nu}=0.059\pm 0.028$, $\Omega_b=0.039\pm 0.014$ and $h=0.70\pm 0.12$ matches observational data best. The 1$\sigma$ (68.3%) confidence limits on each cosmological parameter, which are obtained by marginalizing over the other parameters, are $0.82\le n\le1.39$, $0.19\le\Omega_m\le 1$ ($0\le\Omega_{\Lambda}\le 0.81$), $0\le\Omega_{\nu}\le 0.17$, $0.021\le \Omega_b\le 0.13$ and $0.38\le h\le 0.85$ $1.5\le b_{cl}\le 3.5$. Here $b_{cl}$ is the cluster bias parameter. The best-fit parameters for 31 models which are inside of $1\sigma$ range of the best model are presented. It is shown also that observational data set used here rules out the class of CDM models with $h\ge 0.5$, scale invariant primordial power spectrum, zero cosmological constant and spatial curvature at very high confidence level, $>99.99%$. The corresponding class of MDM models are ruled out at $\sim 95%$ C.L., Comment: 19 pages, 9 figures. Accepted for publication in A&A

The evolution of two-point space correlation function of QSOs is analyzed in the framework of the theory of the large scale structure formation. For given cosmological models the agreement between theoretical predictions and observational data on correlation function of QSOs is achieved by determination of scales of structures R(z), in which could be formed quasars at different redshifts z. It is shown that quasars could be formed in the nucleus of massive galaxies or groups of galaxies owing to merges at their central region. It depends on an amplitude of the power spectrum of the initial matter density fluctuations at galaxy-cluster scales., Comment: 4 pages, 3 figers (Proceedings of Gamow Memorial International Conference "The Universe of Gamow: Origional Ideas in Astrophysics and Cosmology", Odessa, August 16-22, 1999; to be published in "Odessa Astron. Publ.", v.12, 1999)

The possibility of determining MDM model parameters on the basis of observable data on the Abell-ACO power spectrum and mass function is analysed. It is shown that spectrum area corresponding to these data is sensitive enough to such MDM model parameters as neutrino mass $m_{\nu}$, number species of massive neutrino $N_{\nu}$, baryon content $\Omega_b$ and Hubble constant $h\equiv H_0/100km/s/Mpc$. The $\chi^2$ minimization method was used for their determination. If all these parameters are under searching then observable data on the Abell-ACO power spectrum and mass function prefer models which have parameters in the range $\Omega_{\nu}$ ($\sim 0.4-0.5$), low $\Omega_b$ ($\le 0.01$) and $h$ ($\sim 0.4-0.6$). The best-fit parameters are as follows: $N_{\nu}=3$, $m_{\nu}=4.4eV$, $h=0.56$, $\Omega_b\le 0.01$. The high-$\Omega_b\sim 0.4-0.5$ solutions are obtained when mass of neutrino is fixed and $\le 3eV$. To explain the observable excessive power at $k\approx 0.05h/Mpc$ the peak of Gaussian form was introduced in primordial power spectrum. Its parameters (amplitude, position and width) were determined along with the MDM model parameters. It decreases $\chi^2$, increases the bulk motions, but does not change essentially the best-fit MDM parameters. It is shown also that models with the median $\Omega_{\nu}\sim 0.2-0.3$ ($m_{\nu}\sim 2.5$, $N_{\nu}\sim 2-3$) and $\Omega_b=0.024/h^2$, which match constraints arising from cosmological nucleosynthesis and high redshift objects, are not ruled out by these data ($\Delta \chi^2<1$)., Comment: 12 pages, 7 figures, LaTeX (aas2pp4) (Journal of Physical Studies, 1999, V.3, No 1, in press)

We examine the dependence of the spatial two-point correlation function of quasars $\xi_{qq}(r,z)$ at different redshifts on the initial power spectrum in flat cosmological models. Quasars and other elements of the large-scale structure of the universe are supposed to form in the peaks of the scalar Gaussian field of density fluctuations of appropriate scales. Quasars are considered as a manifestation of short-term active processes at the centers of these fluctuations. We propose a method for calculating the correlation function $\xi_{qq}(r,z)$ and show its amplitude and slope to depend on the shape of the initial power spectrum and the scale R of the fluctuations in which quasars are formed. We demonstrate that in the CDM models with the initial power spectrum slope $n=0.7\div1$ it is possible to explain, by choosing appropriate values of R, how the amplitudes and correlation radii of $\xi_{qq}(r,z)$ may either increase or decrease with increasing redshift z. In particular, the correlation radii of $\xi_{qq}(r,z)$ grow from $6-10h^{-1}$ Mpc when R grows from $0.45 h^{-1}$ to $1.3h^{-1}$ Mpc. The H+CDM model at realistic values of R fails to account for the observational data according to which the $\xi_{qq}(r,z)$ amplitude decreases with increasing $z$., Comment: 8 pages, 2 figures

An accurate analytic approximation of the transfer function for the power spectra of primordial density perturbations in mixed dark matter models is presented. The fitting formula in a matter-dominated Universe ($\Omega_0=\Omega_M=1$) is a function of wavenumber $k$, redshift $z$ and four cosmological parameters: the density of massive neutrinos, $\Omega_{\nu}$, the number of massive neutrino species, $N_{\nu}$, the baryon density, $\Omega_{b}$ and the dimensionless Hubble constant, $h$. Our formula is accurate in a broad range of parameters: $k\le 100 h/Mpc$, $z\le 30$, $\Omega_{\nu}\le 0.5$, $N_{\nu}\le 3$, $\Omega_{b}\le 0.3$, $0.3\le h\le 0.7$. The deviation of the variance of density fluctuations calculated with our formula from numerical results obtained with CMBfast is less than 6% for the entire range of parameters. It increases with $\Omega_bh^{2}$ and is less than $\le 3%$ for $\Omega_bh^{2}\le 0.05$. The performance of the analytic approximation of MDM power spectra proposed here is compared with other approximations found in the literature. Our approximation turns out to be closest to numerical results in the parameter space considered here., Comment: 13 pages, 20 figures, LaTeX (l-aa) (accepted by A&A)