Production of scalar particles in cosmological models

The mean number of particles produced in a space-time with the metric ds²=dt²–t² (dx²+dy²)–Kt²dz²(=1/t², 1) is calculated. It is shown that the produced particles are described by a Bose-Einstein distribution with a certain temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–6, July, 1980.I thank D. M. Gitman and V. P. Frolov for discussing a number of questions touched upon in the paper.     

Little higgs models and T parity

Little Higgs models are an interesting extension of the Standard Model at the TeV scale. They provide a simple and attractive mechanism of electroweak symmetry breaking. We review one of the simplest models of this class, the Littlest Higgs model, and its extension with T parity. The model with T parity satisfies precision electroweak constraints without fine-tuning, contains an attractive dark matter candidate, and leads to interesting phenomenology at the Large Hadron Collider (LHC).     

Light singlet particles and their cosmological consequences in witten-type supersymmetric models

In a class of supersymmetric gauge models which generate a large mass scale from a supersymmetry breaking mass scale M through loop corrections, there exists generally a very light scalar particle which transforms like a singlet under SU(3)_c × SU(2)_L with no U(1) charge. Cosmological constraints on such a particle are so severe that an upper bound is set on possible values of supersymmetry breaking scale in this class of models as M ? 500 TeV provided that the large mass scale is 10¹⁵ GeV and the mass of the light scalar particle is generated in one-loop order. This bound holds even if the goldstino is not absorbed into the gravitino.     

Self-similar cosmological models

The kinematics and dynamics of self-similar cosmological models are discussed. The degrees of freedom of the solutions of Einstein's equations for different types of models are listed. The relation between kinematic quantities and the classifications of the self-similarity group is examined. All dust local rotational symmetry models have been found.     

Holographic cosmological models on the braneworld

In this Letter we have studied a closed universe which a holographic energy on the brane whose energy density is described by ρ(H)=3c²H²$\rho (H)=3c^2{H}^2$ and we obtain an equation for the Hubble parameter. This equation gave us different physical behavior depending if c²>1$c^2>1$ or c²<1$c^2<1$ against of the sign of the brane tension.     

Tilted homogeneous cosmological models

We examine spatially homogeneous cosmological models in which the matter content of space-time is a perfect fluid, and in which the fluid flow vector is not normal to the surfaces of homogeneity. In such universes, the matter may move with non-zero expansion, rotation and shear; we examine the relation between these kinematic quantities and the Bianchi classification of the symmetry group. Detailed characterizations of some of the simplest such universe models are given.     

Spatially homothetic cosmological models

Spatially homothetic cosmological models are defined as space-time manifolds acted on by a 3-parameter group of transformations transitive over spacelike hypersurfaces, whose effect is to multiply the metric by a constant conformal factor. Previous work on these models is reviewed briefly and the algebraic classification scheme of Eardley is described. Explicit forms of the metric and group generators are given for each class in terms of a conformally synchronous coordinate system using an invariant orthogonal basis of 1-forms. It is shown that certain subclasses are necessarily incomplete in the sense that a singularity of the conformally synchronous system must develop within a finite time.This article is Dedicated to Achille Papapetrou on the occasion of his retirement and forms a part of the Papapetrou Festschrift.     

Einstein-Cartan-Maxwell-bianchi type-V cosmological models

Exact cosmological solutions of the Einstein- Cartan-Maxwell equations with spin, stiff matter and an electromagnetic field for Bianchi type-V universes are obtained. A class of nonsingular solutions is presented. The most important characteristic of these solutions is that in one case the effect of the electromagnetic field is to reduce the value of the minimum volume while in another case there exists the possibility of enlarging this value arbitrarily.     

Spatially homogeneous cosmological models

We study nonviscous and viscous fluids in Bianchi types II, VIII, and IX space-times under the restriction that the ratio of shear to expansion be constant.     

Charge in cosmological models

The balanced field equations due to Penney are used to find solutions for cosmological models in the presence of charge. Herein, it is found that the introduction of charge adds additional terms to the Einstein conservation equation and distribution expressions. The curvature parameter is affected and it is concluded that whereas matter affects it positively, the charge does so negatively. There then arises also the possibility of an evolution of local systems against the background of a global expansion.     

Effects of cosmological constant on motion of UHECR particles

Recent astronomical observations manifest that about two-thirds of the whole energy in the Universe is contributed by a small positive cosmological constant A (> 0). Then, an asymptotically de Sitter spacetime is premised naturally. However, physics in the de Sitter spacetime is very different from that in the Minkowski spacetime. As the first step, a covariant formalism of the kinematics in the de Sitter spacetime is presented here. By solving exactly the equations of motion for a field, we obtain the dispersion relation of a free particle. It is noticed that the dispersion relation is dependent on the degree of freedom of angular momentum of the particle. We show the threshold anomaly of the ultra high energy cosmic ray disappears naturally in the framework of the de Sitter kinematics.     

Absolute minima of the higgs potential with vanishing cosmological constant in N=1 supergravity GUTs

A necessary condition is derived for the desired vacuum to be an absolute minimum of the scalar potential with vanishing cosmological constant. In the case of a renormalizable GUT-sector this implies the existence of physical light chiral superfields which transform like the Goldstone fields associated with the braking of the GUT-symmetry. Via the renormalization of gauge couplings these lead to a small unification scale and thus to disastrous proton decay rates.     

Oscillatory behavior in cosmological models

Oscillatory behavior in cosmological models is investigated, motivated, in part, by the apparent periodic distribution of galaxies in deep narrow-cone red-shift surveys. In particular, oscillatory behavior in two cosmological models is studied; a qualitative analysis is performed and approximate solutions are found for a soft inflationary model and for a Friedmann-Robertson-Walker model containing a perfect fluid and a scalar field source. These two models are conformally equivalent to particular models arising from a large class of scalar-tensor theories. It is then argued that such oscillatory behavior is a generic property of scalartensor theories of gravity.     

Geodesic Bianchi type cosmological models

Some perfect fluid solutions of Einstein's field equations are obtained in spacetimes with two hypersurface orthogonal space-lika commuting Killing vectors. The flow is assumed to be geodesic. The solutions depend on an arbitrary function of time which determines the equation of state. In the models derived one additional Killing vector exists and the solutions are actually Bianchi-type cosmological models.     

The Bianchi IX cosmological models

Two cosmological models for the Bianchi IX metric are constructed. These include the following sources of gravitation: 1) a co-moving anisotropic liquid, non-comoving dust, and a scalar field; 2) an anisotropic liquid, pure radiation, and a scalar field. The kinematic parameters of the models are found.     

Building analytical three-field cosmological models

A difficult task to deal with is the analytical treatment of models composed of three real scalar fields, as their equations of motion are in general coupled and hard to integrate. In order to overcome this problem we introduce a methodology to construct three-field models based on the so-called “extension method”. The fundamental idea of the procedure is to combine three one-field systems in a non-trivial way, to construct an effective three scalar field model. An interesting scenario where the method can be implemented is with inflationary models, where the Einstein–Hilbert Lagrangian is coupled with the scalar field Lagrangian. We exemplify how a new model constructed from our method can lead to non-trivial behaviors for cosmological parameters.