String cloud and domain walls with quark matter in 5-D Kaluza–Klein cosmological model

In this study Kaluza–Klein Cosmological solutions are obtained for quark matter coupled to the string cloud and domain wall in the context of general relativity. For this purpose Einstein field equations are solved by using anisotropy feature of the universe in the five-dimensional Kaluza–Klein Cosmological model. Also, the features of obtained solutions are discussed.     

Properties of Gravitational Waves in Cosmological General Relativity

The 5D Cosmological General Relativity theory developed by Carmeli reproduces all of the results that have been successfully tested for Einstein's 4D theory. However the Carmeli theory because of its fifth dimension, the velocity of the expanding universe, predicts something different for the propagation of gravity waves on cosmological distance scales. This analysis indicates that gravitational radiation may not propagate as an unattenuated wave where effects of the Hubble expansion are felt. In such cases the energy does not travel over very large length scales but is evanescent and dissipated into the surrounding space as heat.     

Interacting Quintessence Models of Dark Energy

In this paper we consider two models of quintessence scalar fields with different potentials. Interaction with generalized cosmic Chaplygin gas is also investigated. Cosmological parameters are studied and graphical behavior is analyzed. We find that our model is agree with observational data specially ΛCDM model.     

Supersymmetric cosmology with a gauge singlet

Cosmological constraints on a supersymmetric version of the standard model coupled to N = 1 supergravity are derived, in which gauge symmetry breaking is triggered by a Higgs singlet. Possible neutralino dark matter candidates are emphasized. In particular, the fermionic partner of the Higgs singlet is often the lightest supersymmetric particle, with a relic abundance near the critical closure density.     

Casimir effect in quantized R2 gravitation

The Casimir energy is calculated in theories of R² gravitation and conformai gravitation in the space R₁ x T₃, where T₃ is a 3D torus. Cosmological applications of the results are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 59–62, June, 1989.I whish to thank I. L. Bukhbinder for useful discussions.     

Nonlinear Spinor Field in Cosmological Models Without Singularity and Without the Beginning of Time

Russian Physics Journal - Cosmological model describing the Universe without the singularity and without the Beginning, that is, the eternal Universe evolving from the infinite past, is proposed....     

Influence of Thermal Radiation on Singular Behavior of the Universe

Russian Physics Journal - Cosmological models with inhomogeneous viscous fluids and a logarithmic equation of state in the Friedman– Lemaitre–Robertson–Walker Universe are...     

Cosmology is not a renormalization group flow

A critical examination is made of two simple implementations of the idea that cosmology can be viewed as a renormalization group (RG) flow. Both implementations are shown to fail when applied to a massless, minimally coupled scalar with a quartic self-interaction on a locally de Sitter background. Cosmological evolution in this model is not driven by any RG screening of couplings but rather by inflationary particle production gradually filling an initially empty universe with a sea of long wavelength scalars.     

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.     

Yang-Mills cosmologies and collapsing gravitational sphalerons

Cosmological solutions with a homogeneous Yang-Mills field which oscillates and passes between topologically distinct vacua are discussed. These solutions are used to model the collapsing Bartnik-McKinnon gravitational sphaleron and the associated anomalous production of fermions. The Dirac equation is analyzed in these backgrounds. It is shown explicity that a fermion energy level crosses from the negative to positive energy spectrum as the gauge field evolves between the topologically distinct vacua. The cosmological solutions are also generalized to include an axion field.     

Antimatter in the Universe

Cosmological models which predict a large amount of antimatter in the Universe are reviewed. Observational signatures and searches for cosmic antimatter are briefly considered. A short discussion of new long range forces which might be associated with matter and antimatter is presented.     

Gravitationally Non-Degenerate Petrov Type–I Cosmological Model Filled with Viscous Fluid in Modified Brans-Dicke Cosmology

Adding the Cosmological term, which is assumed to be variable in Brans-Dicke theory, we have discussed about a cylindrically symmetric cosmological model filled with viscous fluid with free gravitational field of a non-degenerate petrov type-I. The effect of viscosity on various kinematical parameters has been discussed. Finally, this model has been transformed to the original form (1961) of Brans-Dicke theory (including a variable cosmological term).     

Casimir effect for a massless minimally coupled scalar field between parallel plates in de sitter spacetime

The Casimir effect for massless minimally coupled scalar field is studied. An explicit answer for de Sitter spacetime is obtained and analyzed. Cosmological implications of the result are discussed.     

Variable rest masses in 5-dimensional gravitation confronted with experimental data

Cosmological solutions of Einstein equation for a 5-dimensional space time, in the case of a dust-filled universe, are presented. With these solutions we are able to test a hypothetical relation between the rest mass of a particle and the 5th dimension. Comparison with experiment strongly refutes the implied dependence of the rest mass on the cosmological time.     

Torsion,wormholes, and the problem of the Cosmological constant

We consider the effect of torsion in the early universe to see if it is possible to explain the small value (if not zero) of the Cosmological constant at the present time. For the gauge-theoretic formulation of the Einstein-Cartan theory, we find a wormhole instanton solution which has a minimum (baby universe) radius of the Planck length. The basic difficulty with the wormhole approach is stressed. Finally, we give an explicit calculation from the expression for the evolution of the scale factor, which shows that the spin-dominated interaction term in the very early universe can cancel the Cosmological constant term at that epoch.     

Bianchi type III and Kantowski-Sachs cosmological models in Lyra geometry

Cosmological models for Bianchi type III and Kantowski-Sachs space-times within the framework of Lyra geometry are obtained. The physical behavior of the models is also discussed.     

Bulk Viscosity and Decaying Vacuum Density in Friedmann Universe

We present an isotropic and homogeneous flat cosmological model for bulk viscous fluid distribution. We consider the vacuum density proportional to Hubble expansion parameter and time dependent bulk viscosity related to the velocity and acceleration of universe. The behaviour of resulting solutions are in accordance with recent astronomical observations. The model obtained evolves with a decelerating expansion followed by late time acceleration. Cosmological term Λ being very large at initial epoch relaxes to a genuine cosmological constant asymptotically. Presence of bulk viscosity prevents the matter density to vanish asymptotically and the matter density continues to be of the order of vacuum density after a finite time. Thus, we obtain a universe having the possibility of cosmic coincidence.     

Warm inflation in Horndeski gravity

In this paper, we investigate a class of Horndeski scalar-tensor theory of gravity for warm inflation. We present some models where the early-time acceleration is realized in the weak and in the strong dissipation regime. Cosmological perturbations are analyzed.     

Dark energy versus modified gravity

There is now strong observational evidence that the expansion of the Universe is accelerating. The standard explanation invokes an unknown "dark energy" component. But such scenarios are faced with serious theoretical problems, which has led to increased interest in models where instead general relativity is modified in a way that leads to the observed accelerated expansion. The question then arises whether the two scenarios can be distinguished. Here we show that this may not be so easy, demonstrating explicitly that a generalized dark energy model can match the growth rate of the Dvali-Gabadadze-Porrati model and reproduce the 3+1 dimensional metric perturbations. Cosmological observations are then unable to distinguish the two cases.     

Heavy sterile neutrinos: bounds from big-bang nucleosynthesis and SN 1987A

Cosmological and astrophysical effects of heavy (10–200 MeV) sterile Dirac neutrinos, mixed with the active ones, are considered. The bounds on mass and mixing angle from both supernovae and big-bang nucleosynthesis are presented.