Viscosity and matter creation in the early universe

Mechanical and thermodynamic aspects of the early universe are discussed. Adopting an isotropic and imperfect fluid model, we can introduce one single viscosity coefficient, viz. the bulk viscosity . Allowing for particle creation or annihilation there is room for one additional coefficient, viz. the creation rate . Specializing to the FRW metric we consider the question, discussed in the recent literature, whether the viscosity/creation concepts describe after all one and the same physical process. We conclude that they do not. Thereafter considering the limitations on set by the second law of thermodynamics, we find that it is possible to account for the large nondimensional entropy in the universe (10⁹) by ignoring viscosity altogether, and allowing for a particle sink (<0) of large magnitude being operative during a brief time period. Numerical examples are given.     

On the chemical composition of pregalactic matter

Rostov State University. Translated from Astrofizika, Vol. 30, No. 2, pp. 437–448, March–April, 1989.     

The thermodynamics of early universe

Using the extented Jaynes's principle of maximum entropy we determine the effect of the quantum phenomena on the thermodynamical properties of matter in the early stage of Universe. It is shown that the thermodynamical free energy of the matter of the early Universe becomes very large value due to these quantum phenomena. Both the entropy as well as the free energy of the Universe become singular at the Big Bang.     

Molecules in the early universe

The formation of first molecules, negative Hydrogen ions, and molecular ions in a model of the Universe with cosmological constant and cold dark matter is studied. The cosmological recombination is described in the framework of modified model of the effective 3-level atom, while the kinetics of chemical reactions is described 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 approximately 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 × 10^–13 for H^–, 2.37 × 10^–6 for H₂, 1.26 × 10^–13 for H₂⁺, 1.12 × 10^–9 for HD, and 8.54 × 10^–14 for HeH⁺.     

Neutrinos in the early universe

The neutrinos from the Big Bang or the Cosmic Neutrino Background (CNB) carry precious information from the early epoch when our universe was only 1 s old. Although not yet directly detected, CNB may be revealed indirectly through cosmological observations due to neutrino important cosmological influence.We review the cosmological role of neutrinos and the cosmological constraints on neutrino characteristics. Namely, we discuss the impact of neutrinos in the early universe: the cosmic expansion, neutrino decoupling, the role of neutrinos in the primordial production of light elements, leptogenesis, etc. We briefly discuss the role of neutrino at later stages of the universe.Due to the considerable cosmological influence of neutrinos, cosmological bounds on neutrino properties from observational data exist. We review the cosmological constraints on the effective number of neutrino species, neutrino mass and mixing parameters, lepton number of the universe, presence of sterile neutrino, etc.     

Missing dark matter in the local universe

A sample of 11 thousand galaxies with radial velocities V _LG < 3500 km/s is used to study the features of the local distribution of luminous (stellar) and dark matter within a sphere of radius of around 50 Mpc around us. The average density of matter in this volume, ?? _m,loc = 0.08 ± 0.02, turns out to be much lower than the global cosmic density ?? _m,glob = 0.28 ± 0.03. We discuss three possible explanations of this paradox: 1) galaxy groups and clusters are surrounded by extended dark halos, the major part of the mass of which is located outside their virial radii; 2) the considered local volume of the Universe is not representative, being situated inside a giant void; and 3) the bulk of matter in the Universe is not related to clusters and groups, but is rather distributed between them in the form of massive dark clumps. Some arguments in favor of the latter assumption are presented. Besides the two well-known inconsistencies of modern cosmological models with the observational data: the problem of missing satellites of normal galaxies and the problem of missing baryons, there arises another one??the issue of missing dark matter.     

The interaction of matter and radiation in a hot-model universe

In this paper we continue the investigation initiated by Weymann as to the reason why the spectrum of the residual radiation deviates from a Planck curve. We shall consider the distortions of the spectrum resulting from radiation during the recombination of a primeval plasma. Analytical expressions are obtained for the deviation from an equilibrium spectrum due to Compton scattering by hot electrons. On the basis of the observational data it is concluded that a period of neutral hydrogen in the evolution of the universe is unavoidable. It is shown that any injection of energy att>10¹⁰ sec (red shiftz<10⁵) leads to deviation from an equilibrium spectrum.Translated by Peter Foukal.     

Fundamental interactions in the early universe

A unified approach to fundamental interactions as explored earlier is further elaborated and its consequences for the early universe studied especially in connection with the energy dependence of the coupling constants.     

The large-scale structure of the universe in skewed cold dark matter models

We present results from N-body simulations of the clustering properties of the universe in a cubic box of size 260h⁻¹ Mpc, within a cold dark matter (CDM) cosmology with skewed distributions for initial adiabatic density perturbations δ_M. We consider two non-Gaussian models, Chi-squared and Lognormal, where the primordial gravitational potential is obtained from a non-linear transformation on a Gaussian random field. Our procedure yields for each model two primordial density distributions with opposite skewness δ³_M. The gravitational evolution and the present statistical properties of our simulations are strongly sensitive to the sign of the initial skewness. Skew-positive simulations produce a highly lumpy distribution with little power on large scales. Skew-negative simulations, on the contrary, evolve towards a cellular structure with high power on large scales, showing, in many respects, better agreement with observations than the standard CDM model. Giving up the random-phase hypothesis for primordial perturbations seems then a viable possibility to reproduce the large-scale properties of the universe; such a possibility is further motivated by many physical models either within the inflationary dynamics or phase transitions in the early universe.     

Some enigmatic aspects of the early universe

Matter collapsing to a singularity in a gravitational field is still an intriguing question. Similar situation arises when discussing the very early universe or a universe recollapsing to a singularity. It was suggested that inclusion of mutual gravitational interactions among the collapsing particles can avert a singularity and give finite value for various physical quantities. We also discussed how inclusion of large dark energy term compensates for the net gravity. The discussion is taken further by including the effects of charge, magnetic fields and rotation. The role of large extra dimensions under the extreme initial conditions is discussed and possible connection with the cyclic brane theory is explored. We constrain various cosmic quantities like the net charge, number density of magnetic monopoles, primordial magnetic fields, size of the extra dimensions, etc. We are also able to arrive at the parameters governing the observed universe.     

QSOs as probes of the early universe

The spectrum of the highest redshift QSO 2000–330 (z=3.78) contains four heavy-element absorption systems withz _abs>3.0. Interesting features include velocity structure atz _abs=3.552 which suggests a cluster origin and a purely low ionization system atz _abs=3.1881 typical of a galactic disk sightline.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Conformally invariant model of the early universe

A model of the early universe in the Einstein theory of gravitation, supplemented by a conformalty invariant version of the Weinberg—Salam model, is considered. The conformai symmetry principle leads to the need to eliminate the Higgs potential from the expression for gravitational action, using the Lagrangian density of the model of Weinberg—Salam electroweak interactions as the material source, and to incorporate the conformally invariant Penrose—Chernikov—Tagirov term. In the limit of flat space, we arrive at the a version of the Weinberg—Salam model without Higgs particle-like excitations. In the conformalty invariant model under consideration, Higgs fields are absorbed by the spatial metric, so one can assume that the masses of elementary particles originate at the time when the evolution of the universe begins. Translated from Astrofizika, Vol. 41, No. 3, pp. 459–471, July–September, 1998.     

Main stages of evolution of matter in the universe. I

The problem of the equation of state of cosmic matter is discussed and the constants of integration in the Friedmann solutions are determined. Translated from Astrofizika, Vol. 40, No. 1, pp. 117–124, January–March, 1997.     

Baryonic fraction in the cold plus hot dark matter universe

The observational infrared spectra of a number of Wolf–Rayet stars of WC8–9 spectral classes are shown to be quite satisfactorily explained by making use of the detailed theoretical model of a dust shell made up of spherical amorphous carbon grains, the dynamics, growth–destruction, thermal and electrical charge balance of which are taken into account. The dust grains acquire mainly positive electrical charge, move with suprathermal drift velocities and may grow up to 100–200 Å as a result of implantation of impinging carbon ions. For most of the stars the fraction of condensed carbon does not exceed 1 per cent. While the nature of the grain nucleation remains unknown, the condensation distances and the grain seed production can be estimated by fitting the observational spectra with theoretical ones.     

The chemical composition of the Sun

We present a redetermination of the solar abundances of all available elements. The new results have very recently been published by Asplund et al. (Annu. Rev. Astron. Astrophys. 47:481, 2009). The basic ingredients of this work, the main results and some of their implications are summarized hereafter.     

Main stages of evolution of matter in the universe. II

A possible scenario for the evolution of the universe following the big bang at t > 10^-5 sec is considered. The necessary conditions that must be present for the formation of stars and stellar systems to be possible are formulated. As a condition for the formation of stars we take kT_s≤ GM_sm_p(3R), and for stellar systems HR ? (GM/R)^1/2, where T_s is the temperature of the cosmic plasma, m_p is the mass of a proton, M_s is the mass of a star, M is the mass of a stellar cluster, R is the radius of these celestial bodies, and H is the bubble parameter for the corresponding time. In accordance with these criteria, we assume that in the course of cosmological expansion, neutron stars should have been formed first (times 2.10^-4 ? t ? 1 sec, densities 0.07 ? ρ_B? 2.10⁴ g/cm³) and then, in chronological order, appeared white dwarfs (t ≈ 10² sec, ρ_B ? 5.10^-3 g/cm³), ordinary stars (t ≈ 4.10⁶ sec, ?_B ≈ 10^-11 g/cm³), galactic nuclei (t ≈ 3.10¹¹ sec, ?_B ≈ 5.10^-19 g/cm³, globular clusters (t ≈ 10¹³ sec, ?_B ≈ 4.10^-21 g/cm³), and galaxies (t ≈ 10¹⁵ sec, ?_B ≈ 10^-24 g/cm³), where ?_B is the average density of ordinary (baryon) matter in the universe. It is shown that a galactic nucleus is a stellar system in statistical equilibrium and consists mainly of neutron stars and white dwarfs. The formation of some pulsars (neutron stars with angular rotation rates 1 < Ω < 200 sec^-1) may occur in a galactic nucleus. Observed pulsars should therefore contain some fraction of neutron stars from the nucleus of the Galaxy that were able to escape it over the relaxation time (the tail of the Maxwell distribution, with star velocities v > v₀, where v₀ is the velocity corresponding to the work function 2GMM_s/R, M being the mass and R the radius of the Galaxy’s nucleus.     

Remarks on the viscosity concept in the early universe

Some aspects of viscous cosmological models, mainly of Bianchi type-I, are studied, in particular with the purpose of trying to obtain a natural explanation of why the entropy per baryon in the universe, ~ 10⁹, is so large. Using the FRW metric it is first shown, in agreement with previous workers, that the expressions for the bulk viscosity as derived from kinetic theory in the plasma era is incapable of explaining the large value of. However it is possible to imagine the viscosity to be an impulse viscosity operative in one or several phase transitions in the early universe. This is the main idea elaborated on in the present paper. It is shown that in thek = 0 FRW space, an impulse bulk viscosity _infl ~ 10⁶⁰ g cm^–1 s^–1) acting at the phase transition at the end of the inflationary epoch corresponds to the correct entropy. If the space is anisotropic, it is natural to exploit the analogy with classical fluid dynamics to introduce the turbulent viscosity concept. This is finally discussed, in relation to an anisotropy introduced in the universe via the Kasner metric.     

Forming supermassive black holes like J1342+0928 (invoking dark matter) in early universe

Recent discovery of J1342+0928 using data from the WISE telescope and ground based surveys indicate presence of a supermassive black hole (SMBH) having a mass of 800 million solar mass at a redshift of about 7.6. This imply that the black hole grew to this mass only 690 million years after the universe started expanding. Here we suggest that formation of such SMBH’s so early in the universe is consistent with our present understanding of the phenomena involved by invoking dark matter (DM).