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.     

The formation of the first luminous objects in the universe

Paramount among the processes that ended the cosmic dark ages must have been the emergence of a first generation of stars. I review recent results on their formation out of metal-free gas, and discuss related open questions that still defy our understanding. This revised version was published online in August 2006 with corrections to the Cover Date.     

Which are the most luminous objects in the universe?

Using the Eddington luminosity function as well as observational results, it was shown that the supernovae of type II are the most luminous objects in the universe while emitting prompt neutrinos in their early collapsing phase.     

Scale transformations and evolution of the early universe

The notion of discrete scale transformations is invoked to suggest strong links between fundamental interactions and cosmology giving rise to a hierarchy of cosmic scales.     

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.     

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.     

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.     

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.     

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.     

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.     

Maximum acceleration and magnetic field in the early universe

The maximum acceleration at the Planck epoch is shown to be related to the maximum magnetic field and curvature as well as temperature in that era. Spin-torsion effects at that epoch also lead to same value.     

The chemical composition of matter in the early universe

The results of the computations of the chemical evolution for a galaxy cluster are presented. The matter exchange between galaxies and intergalactic medium is taken into account. Two dependences of star formation rate on time are considered: (i) monotonously decreasing dependence characteristic of elliptical galaxies, (ii) dependence having two peaks associated with creation of spiral galaxy subsystems, with suppression of star formation at the period between maxima. It is assumed that galactic ejection is due to explosions of II-type supernova with massesm5M , and that the accretion on to a galaxy depends but weakly on the time. By comparing the obtained results with total combination of available observations, it is established that the rate of gaseous exchange between a galaxy and intergalactic medium should be rather large: 0.03M _gal Gyr^–1. Besides, the activity of each type of galaxy leads to an approximately equal enrichment of intergalactic gas by new elements synthesized in the stars. The existence of a large accretion on to the Galaxy leads to the decrease of primordial deuterium abundance by a factor of no more than 2 during the galaxy evolution time. It enables us to assume that the standard Big Bang model with baryon density parameter _b 0.1 may be considered as true.     

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.     

Nonlinear curvature Lagrangians and extended inflation in the early universe

Theories with Lagrangians nonlinear in the curvature scalar can be reduced by appropriate transformations to a form similar to the Brans-Dicke model. This may enable us to have extended inflation in the early universe without the difficulties of introducing scalar fields.     

Unified description of early universe in scalar-tensor theory

A spatially homogeneous and isotropic Robertson-Walker model with zero-curvature of the universe is studied in Saez-Ballester scalar-tensor theory. Exact solutions of the field equations are obtained for two different early phases of the universe viz. the inflationary and the radiation-dominated phases by using gamma-law equation of state p=(γ-1)ρ in the presence of perfect fluid. The γ-index describing the material content varies continuously with cosmic time so that in the course of its evolution, the universe goes through a transition from an inflationary phase to a radiation-dominated phase. The coupling parameterω is allowed to depend on the cosmic time. The nature of scalar field and other physical significance have also been discussed. This revised version was published online in July 2006 with corrections to the Cover Date.