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V. N. Lukash

Publications and source records attributed to V. N. Lukash.

At least 37 records · Page 2Linked to original sources
arXiv2011

From the cosmological model to generation of the Hubble flow

We review different approaches to the problem of generating the observed Hubble flow, whose discussion was pioneered by A.D. Sakharov. Extrapolating the Cosmological Standard Model to the past makes it possible to determine physical properties of and conditions in the early universe. We discuss a new cosmogenesis paradigm based on studying geodesically complete geometries of black/white holes with integrable singularities.

astro-ph.CO↗
arXiv2011

Geometries with integrable singularity -- black/white holes and astrogenic universes

We briefly review the problem of generating cosmological flows of matter in GR (the genesis of universes), analyze models' shortcomings and their basic assumptions yet to be justified in physical cosmology. We propose a paradigm of cosmogenesis based on the class of spherically symmetric solutions with {\it integrable} singularity $r=0$. They allow for geodesically complete geometries of black/white holes, which may comprise space-time regions with properties of cosmological flows.

astro-ph.CO↗
arXiv2008

Dark energy: myths and reality

We discuss the questions related to dark energy in the Universe. We note that in spite of the effect of dark energy, large-scale structure is still being generated in the Universe and this will continue for about ten billion years. We also comment on some statements in the paper ``Dark energy and universal antigravitation'' by A.D. Chernin [4].

astro-ph↗
arXiv2007

Analytical approximation of the emission line Fe $K_α$ in QSO's spectra

In spectra of many Seyfert galaxies there is a wide emission line of Fe $K_α$. The line profile with two maxima supposes that the line emerges in innermost regions of an accretion disk around a black hole, hence, it is necessary to take into account General Relativity (GR) effects. In order to determine GR processes which occur in active galactic nuclei (AGN) an inverse problem of reconstructing the accreting system parameters from the line profile has to be solved quickly. In this paper we present a numerical approximation of the emission line Fe $K_α$ with analytical functions. The approximation is accomplished for a range of the disk radial coordinate $r$ and the angle $θ$ between line of sight and perpendicular to the disk and allows one to decrease computing time by $10^6$ times in certain astrophysical problems taking into account all GR effects. The approximation results are available in the Internet at http://www.iki.rssi.ru/people/repin/approx

astro-ph↗
arXiv2003

Mass function of gravitationally bounded objects in the inhomogeneous Universe

We modify the Press-Schechter formalism to calculate the mass function of gravitationally bounded objects in a local Universe with size $L> 10h^{-1}$Mpc, i.e. separately in voids ($Ω_{m,L}<Ω_m$) and superclusters ($Ω_{m,L}>Ω_m$). The dependence of the abundance of gravitationally bounded objects on local matter density is analyzed.

astro-ph↗
arXiv2002

Magnetic fields in AGNs and microquasars

Observations of AGNs and microquasars by ASCA, RXTE, Chandra and XMM-Newton indicate the existence of wide X-ray emission lines of heavy ionized elements in their spectra. The emission can arise in the inner parts of accretion discs where the effects of General Relativity (GR) must be counted, moreover such effects can dominate. We describe a procedure to estimate an upper limit of the magnetic fields in the regions where X-ray photons are emitted. We simulate typical profiles of the iron $K_α$ line in the presence of a magnetic field and compare them with observational data. As an illustration we find $H < 10^{10} - 10^{11}$ Gs for Seyfert galaxy MCG--6--30--15. Using the perspective facilities of measurement devices (e.g. Constellation-X mission) a better resolution of the blue peak structure of iron $K_α$ line will allow to find the value of the magnetic fields if the latter are high enough.

astro-ph↗
arXiv2002

Abundance and evolution of galaxy clusters in cosmological models with massive neutrino

The time evolution of the number density of galaxy clusters and their mass and temperature functions are used to constrain cosmological parameters in the spatially flat dark matter models containing a fraction of hot particles (massive neutrino) additional to cold and baryonic matter. We test the modified MDM models with cosmic gravitational waves and show that they neither pass the cluster evolution test nor reproduce the observed height of the first acoustic peak in $ΔT/T$ spectrum, and therefore should be ruled out. The models with a non-zero cosmological constant are in better agreement with observations. We estimate the free cosmological parameters in $Λ$MDM with a negligible abundance of gravitational waves, and find that within the parameter ranges $h\in (0.6, 0.7)$, $n\in (0.9, 1.1)$, (i) the value of $Ω_Λ$ is strongly affected by a small fraction of hot dark matter, $f_ν\equivΩ_ν/Ω_m\in (0, 0.2)$: $0.45 <Ω_Λ<0.7$ ($1σ$ CL), and (ii) the redshift evolution of galaxy clusters alone reveals the following explicit correlation between $Ω_Λ$ and $f_ν$: $Ω_Λ+0.5f_ν=0.65\pm 0.1$. The present accuracy of observational data allows only to bound the fraction of hot matter, $f_ν\in (0, 0.2)$ (the number of massive neutrino species remains undelimited, $N_ν=1, 2, 3$).

astro-ph↗
arXiv2001

Cosmological implications of galaxy clusters: best-fit models

The galaxy cluster power spectrum and mass/temperature functions are currently the most precise observational tools for constraining the theory of the formation of large scale structure (LSS) in the Universe. Complementing these tests by the observational data at larger (cosmic microwave backgroud anisortopy (CMBA)) and smaller (distribution of $Ly_α$ clouds) scales opens the way to a straightforward determination of the cosmological parameters in simplest dark matter (DM) models. We argue that such a 'minimal data set' is free from systematic effects and can indicate quite precisely the parameters of spatially flat mixed DM model with a positive cosmological constant and no cosmic gravitational waves.

astro-ph↗
arXiv2001

Evolution of galaxy clusters in $Λ$MDM cosmologies

The time evolution of galaxy cluster abundance is used to constrain cosmological parameters in dark matter models containing a fraction of hot particles (massive neutrino). We test the modified MDM models with cosmic gravitational waves which are in agreement with observational data at $z=0$, and show that they do not pass the cluster evolution test and therefore should be ruled out. The models with a non-zero cosmological constant are in better agreement with the evolution test. We estimate $Ω_Λ$ and find that it is strongly affected by a small fraction of hot dark matter: $0.4 <Ω_Λ<0.8$ for $Ω_H /Ω_M <0.2$.

astro-ph↗
arXiv2000

Generalised inflation with a gravitational wave background

We propose a Lambda-inflation model which explains a significant part of the COBE signal by primordial cosmic gravitational waves. The primordial density perturbations fulfill both the constraints of large-scale microwave background and galaxy cluster normalization. The model is tested against the galaxy cluster power spectrum and the high-multipole angular CMB anisotropy.

astro-ph↗
arXiv2000

Current status of cosmological MDM model

An analysis of cosmological models in spatially flat Friedmann Universe with cosmic gravitational wave background and zero $Λ$-term is presented. The number of free parameters is equal to 5, they are $σ_8$, $n$, $Ω_ν$, $Ω_b$, and $h$. The normalization of the spectrum of density perturbations on galaxy cluster abundance ($σ_8 = 0.52\pm 0.04$) has been used to calculate numerically the value of the large scale CMB anisotropy ($\ell\simeq 10$) and the relative contribution of cosmological gravitational waves T/S. Increasing $Ω_ν$ weaken the requirements to the value of T/S, however even for $Ω_ν\le 0.4$ the models with $h+n\ge 1.5$ suggest considerable abundance of gravitational waves: T/S${}^>_\sim 0.3$. In models with $Ω_ν\le 0.4$ and scale-invariant spectrum of density perturbations ($n=1$): T/S${}^>_\sim 10(h-0.47)$. Minimization of the value T/S is possible only in the range of the red spectra ($n<1$) and small $h$ ($<0.6$). It is shown that the models with T/S$\in [0, 3]$ admit both moderate red and blue spectra of density perturbations, $n\in[0.9,1.2]$, with rather high abundance hot dark matter, $Ω_ν\in [0.2,0.4]$. Any condition, $n<0.9$ or $Ω_ν<0.2$, decreases the relative amplitude of the first acoustic peak for more than 30% in comparison with its hight in the standard CDM normalized by COBE data.

astro-ph↗
arXiv2000

A generalized inflation model with cosmic gravitational waves

We propose a $Λ$-inflation model which explains a large fraction of the COBE signal by cosmic gravitational waves. The primordial density perturbations fulfil both the contraints of large-scale microwave background and galaxy cluster normalization. The model is tested against the galaxy cluster power spectrum and the high-multipole angular CMB anisotropy.

astro-ph↗
arXiv2000

Determination of cosmological parameters from large scale structure observations

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-$α$ clouds and CMB temperature fluctuations is analyzed. Using a $χ^2$ minimization method, assuming $Ω_Λ+Ω_m =1$ and no contribution from gravity waves, we found that a tilted $Λ$MDM model with one sort of massive neutrinos and the parameters $n\approx 1.12$, $Ω_m\approx 0.4$ ($Ω_Λ\approx 0.6$), $Ω_{cdm}\approx 0.3$, $Ω_ν\approx 0.06$, $Ω_b\approx 0.04$ and $h\approx 0.7$ matches observational data best. $Ω_ν$ is higher for more species of massive neutrinos, $\sim 0.1$ for two and $\sim 0.13$ for three species. $Ω_m$ 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.

astro-ph↗
arXiv2000

Cosmological parameters from large scale structure observations

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-$α$ clouds and CMB temperature fluctuations is analyzed. Using a $χ^2$ minimization method, assuming $Ω_Λ+Ω_{\rm{matter}} =1 $ and no contribution from gravity waves, we found that a tilted $Λ$MDM model with one sort of massive neutrinos and the parameters $n=1.12\pm 0.10$, $Ω_m=0.41\pm 0.11$ ($Ω_Λ=0.59\pm0.11$), $Ω_{cdm}=0.31\pm 0.15$, $Ω_ν=0.059\pm 0.028$, $Ω_b=0.039\pm 0.014$ and $h=0.70\pm 0.12$ matches observational data best. The 1$σ$ (68.3%) confidence limits on each cosmological parameter, which are obtained by marginalizing over the other parameters, are $0.82\le n\le1.39$, $0.19\leΩ_m\le 1$ ($0\leΩ_Λ\le 0.81$), $0\leΩ_ν\le 0.17$, $0.021\le Ω_b\le 0.13$ 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 $1σ$ 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.

astro-ph↗
arXiv1999

The very early Universe

In these lectures we dwell upon the cosmological corner-stones of the Very Early Universe (VEU) theory: Parametric Amplification Effect (PAE) responsible for the generation of Primordial Cosmological Perturbations (PCPs), Chaotic and Stochastic Inflation, Principal Tests of VEU, and others.

astro-ph↗
arXiv1999

Lambda-inflation and CMB anisotropy

We explore a broad class of three-parameter inflationary models, called the $Λ$-inflation, and its observational predictions: high abundance of cosmic gravitational waves consistent with the Harrison-Zel'dovich spectrum of primordial cosmological perturbations, the non-power-law wing-like spectrum of matter density perturbations, high efficiency of these models to meet current observational tests, and others. We show that a parity contribution of the gravitational waves and adiabatic density perturbations into the large-scale temperature anisotropy, T/S $\sim 1$, is a common feature of $Λ$-inflation; the maximum values of T/S (basically not larger than 10) are reached in models where (i) the local spectrum shape of density perturbations is flat or slightly red ($n_S{}_\sim^< 1$), and (ii) the residual potential energy of the inflaton is near the GUT scale ($V_0^{1/4} \sim 10^{16} GeV$). The conditions to find large T/S in the paradigm of cosmic inflation and the relationship of T/S to the ratio of the power spectra, $r$, and to the inflationary $γ$ and Hubble parameters, are discussed. We argue that a simple estimate, T/S$\simeq 3r\simeq 12γ\simeq (\frac{H}{6\times 10^{13}{\rm GeV}})^2$, is true for most known inflationary solutions and allows to relate straightforwardly the important parameters of observational and physical cosmology.

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