Cosmological models with constant deceleration parameter and bulk viscous mode

Recently Berman and Gomide have presented cosmological models with a constant deceleration parameter in general relativity without assuming a specific equation of state. It is shown that these models are equivalent to those with bulk viscosity. Some general remarks are made on the former models, including implications for violations of causality.     

Cosmological models with rotation

Nonstationary and stationary cosmological models with rotation and the Bianchi IX metric are constructed within the general relativity theory. A comoving anisotropic liquid and non-comoving “dust-like liquid” are the sources of gravitation in one case, while a comoving anisotropic, non-comoving “dust-like liquid”, and pure radiation - in the other. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 33–37, August, 2008.     

Cosmological constraints on bulk neutrinos

Recent models invoking extra space-like dimensions inhabited by (bulk) neutrinos are shown to have significant cosmological effects if the size of the largest extra dimension is R greater, similar 1 fm. We consider effects on cosmic microwave background anisotropies, big bang nucleosynthesis, deuterium and 6Li photoproduction, diffuse photon backgrounds, and structure formation. The resulting constraints can be stronger than either bulk graviton overproduction constraints or laboratory constraints.     

Cosmological models

An LRS Bianchi type II cosmological model is built with a state equation that is a function of the cosmic timet. The ratiop/ is 1/3 whent 0 and is insignificant whent. Thus, the matter content behaves like radiation for smallt and like dust for larget.     

Cosmological models with Yang-Mills fields

Cosmological models with an SU(2) Yang-Mills field are studied. For a specific model with a minimally coupled Yang-Mills Lagrangian, which includes an arbitrary function of the second-order term and a fourth-order term, a corresponding reconstruction program is proposed. It is shown that the model with minimal coupling has no de Sitter solutions, for any nontrivial function of the second-order term. To get de Sitter solutions, a gravitational model with nonminimally coupled Yang-Mills fields is then investigated. It is shown that the model with non-minimal coupling has in fact a de Sitter solution, even in absence of the cosmological constant term.     

Cosmological constraints on elementary particle masses in lemaǐtre cosmological models

We recalculate the cosmological limits on hypothetical and undetected elementary particle masses under the assumption that the cosmological constant, Λ, is non-zero. The existing range of allowed masses is considerably extended by removing the unverified assumption that Λ=0. In particular, light neutrino masses up to ≈280 eV are compatible with cosmological observations. The implications of a cold early universe for these estimates are also outlined.     

Cosmological models with constant deceleration parameter

Berman presented elsewhere a law of variation for Hubble's parameter that yields constant deceleration parameter models of the universe. By analyzing Einstein, Pryce-Hoyle and Brans-Dicke cosmologies, we derive here the necessary relations in each model, considering a perfect fluid.     

Sonically produced heat in a fluid with bulk viscosity and shear viscosity

In a viscous fluid, sound produces heat in a spatial pattern which, in general, depends on the relative magnitudes of the shear viscosity coefficient eta and the bulk viscosity coefficient B'. It is well known that when the particle velocity components ui relative to Cartesian coordinates xi are given for an arbitrary sound field, or any field of flow, the volume rate of heat production qv can be determined from a dissipation function in the form B'T1 + eta T2. Here, T1 and T2 are quadratic functions involving derivatives of the type delta ui/delta xj. In this paper, examples are discussed for continuous monofrequency sound fields, including crossed plane waves, as well as focused and unfocused fields. In these examples, spatial distributions of the time-averaged quantity [qv] for media in which the loss mechanism is primarily bulk viscosity are compared to those for media in which shear viscosity dominates.     

Cosmological models and Non-denumerable singularities

A review of the standard cosmological models shows that the positive cosmological constant gives rise to exponential increase in spatial extension. Such an increase is contradictory if extended over infinite future time, since even in an infinite universe there can only be a denumerable infinity of finite spatial units. The argument against exponential expansion is among the processes forbidden by the steady-state postulate of MacMillan.     

Cosmological twinlike models with multi scalar fields

In this study, we consider cosmological models driven by several canonical or noncanonical scalar fields, and we show the manner in which twinlike models for a canonical model can be constructed from noncanonical ones using the superpotential method. We conclude that it is possible to construct twinlike models for multifield cosmological models, even with a nonzero spatial curvature.This work extends the discussions of [D. Bazeia, and J. D. Dantas, Phys. Rev. D 85, 067303(2012)] to cases with multi scalar fields and with non-vanished spatial curvature, by using a different superpotential method.     

Cosmological Friedman models with the charged vacuum

Exact solutions corresponding to the stable charged vacuum are obtained for cosmological Friedman models with a charged scalar field. It is demonstrated that the presence of a massive vector field for the vacuum changes the law of expansion at early stages of evolution of the universe. A method for construction of solutions with the charged vacuum for an O(N) invariant scalar multiplet is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 19–24, December, 1985.     

Cosmological models without singularities

A previously studied theory of gravitation in flat space-time [Petry, W. (1981).Gen. Rel. Grav. 13, 865] is applied to homogeneous and isotropic cosmological models. There exist two different classes of models without singularities: (i) ever-expanding models, (ii) oscillating models. The first class contains models with hot big bang. For these models we get at the beginning of the universe—in contrast to Einstein's theory—very high but finite densities of matter and radiation with a big bang of very short duration. After short time these models pass into the homogeneous and isotropic models of Einstein's theory with spatial curvature equal zero and cosmological constant 0.     

Cosmological models and latest observational data

In this note, we consider the observational constraints on some cosmological models by using the 307 Union type Ia supernovae (SNIa), the 32 calibrated gamma-ray bursts (GRBs) at z>1.4, the updated shift parameter R from WMAP 5-year data (WMAP5), and the distance parameter A of the measurement of the baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red galaxies with the updated scalar spectral index n _s from WMAP5. The tighter constraints obtained here update the ones obtained previously in the literature.     

Exact solutions in Brans-Dicke theory with bulk viscosity

The effect of bulk viscosity on the evolution of the homogeneous and isotropic cosmological models in the Brans-Dicke theory of gravitation is studied. Solutions are found, with a baratropic equation of state, a time-independent bulk viscosity, the gravitational constant inversely proportional to the age of the universe, and the mass of the universe (in the closed model) proportional to the square of its age; the expansion factor is a linear function of the cosmological time. For flat space, power law expansions are found, among them one that is related to extended inflation.