Solution of dirac equation in a singularity-free Kaluza-Klein cosmological model

The singularity-free solution of (4 + D) -dimensional Einstein field equations for the Kaluza-Klein cosmological model is obtained. Then the Dirac equations are solved in this model.     

A singularity-free cosmological model in ECSK theory

In the framework of the ECSK [Einstein-Cartan-Sciama-Kibble] theory of cosmology, a scalar field nonminimally coupled to the gravitational field is considered. For a Robertson-Walker open universe (k=0) in the radiation era, the field equations admit a singularity-free solution for the scale factor. In theory, the torsion is generated through nonminimal coupling of a scalar field to the gravitation field. The nonsingular nature of the cosmological model automatically solves the flatness problem. Further absence of event horizon and particle horizon explains the high degree of isotropy, especially of 2.7-K background radiation.     

Quantum effects in five-dimensional Kaluza-Klein theory

The role of quantum effects in five-dimensional Kaluza-Klein theory is discussed. We concentrate in particular on the evaluation of terms in the one-loop effective action which look like the Maxwell action. A detailed discussion of the reduction of the five-dimensional gravitational action to an equivalent four-dimensional form is given. Self-consistent solutions of the form R⁴ x S¹ are examined. We consider how the inclusion of quantized matter fields into the five-dimensional theory can change results based only on quantum gravitational effects. The importance of including the induced Maxwell term is stressed. It is also noted how a finite renormalization of the one-loop effective action is important.     

Temperature effects in five-dimensional Kaluza-Klein theory

We examine the combined effectsof thermal and quantum-mechanical fluctuations in a Kaluza-Klein universe with a single compact spatial dimension of length ${\overline{L}}_5$. From the one-loop effective potential for ${\overline{L}}_5$ two types of instability are evident. If initially ${\overline{L}}_5$ is less than a temperature-dependent critical length, ${\overline{L}}_5$ will shrink at least down to a length comparable to the Planck length. This instability has been noted by Appelquist and Chodos in the zero-temperature limit. If, on the other hand, ${\overline{L}}_5$ starts out larger than the critical length, it will tend to increase. This result suggests that temperature effects may play an important role in Kaluza-Klein cosmological models.     

Quantum vacuum energy and singularity-free Kaluza-Klein cosmology

We present a class of cosmological models in which vacuum collapse to curvature singularity is prevented by the generalized gravitational Casimir energy. The mechanism works in higher dimensions, and gives rise to Kaluza-Klein cosmologies free from singularity.     

Plane-wave solutions in five-dimensional Kaluza-Klein theories

Exact solutions representing mixed plane-electromagnetic and planegravitational waves in five-dimensional Kaluza-Klein theories are obtained. Two extreme cases, corresponding to the plane waves of the four-dimensional Einstein-Maxwell theory and the dilation waves, respectively, are discussed. In addition, it is found that the five-dimensional harmonic condition is reduced to the usual four-dimensional harmonic condition plus the Lorentz condition.     

Cosmological compactification in Kaluza-Klein model and time-dependent cosmological term

Einstein's equations for the generalized (4+D)-dimensional Robertson-Walker model are solved taking the conformally invariant action for the matter field. Compactification of this model is discussed and the compactification time/compactification mass scale for different values ofD is calculated. The resulting 4-dimensional action for gravity is obtained. It is found that a time-dependent cosmological constant is induced which is very large when the cosmic time is small and very small when the cosmic time is large.     

Phantom scalar fields in five-dimensional Kaluza-Klein theory

The existence of a so-called "phantom" scalar field in some Riemannian spaceV ₄, i.e., a field in which the effective energy momentum tensorT ^(sf) vanishes in the five-dimensional Kaluza-Klein theory, is investigated by means of the integrability conditions for relations of the form _;;=k_,,+bg found in [6]. Phantom fields are found in homogeneous isotropic cosmological models.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 50–56, February, 1996.     

Derivation of a Bogomol'ny inequality in five-dimensional Kaluza-Klein theory

We prove an inequality bounding the mass from below by the electromagnetic charge in five-dimensional Kaluza-Klein theory without assuming the existence of globalU(1) symmetry.Supported in part by NSF-Grant No. PHY-8318350     

The geodesic equation in five-dimensional relativity theory of Kaluza-Klein

In five-dimensional relativity theory of Kaluza-Klein the projection of the 5-geodesic equation is discussed in detail. The scalar occurring within this framework is first assumed to be variable. A simple classification of 5-geodesics is found and pictured with the help of a deformed 5-cone. On the assumption that the scalar is constant the 5-geodesic equation yields the Lorentz equation of motion for a charged particle. Intrinsic mass and intrinsic charge are introduced as new particle parameters. Mass and charge formulas are proposed.     

Cylindrically symmetric cosmological models in Kaluza-Klein spacetime

We consider a non-diagonal cylindrically symmetric metric in the Kaluza-Klein spacetime. We obtain a number of homogeneous and inhomogeneous perfect fluid cosmological models, which include the 5-dimensional analogue of the recently found 4-dimensional non-singular stiff fluid model. Amongst the homogeneous models, which are all as expected big-bang singular, there is the 5-dimensional version of the Friedman-Robertson-Walker flat model.     

Hierarchy problem and the cosmological constant in a five-dimensional Brans-Dicke brane world model

We discuss a new solution, admitting the existence of dS ₄ branes, in five-dimensional Brans-Dicke theory. It is shown that, due to a special form of a bulk scalar field potential, for certain values of the model parameters the effective cosmological constant can be made small on the brane, where the hierarchy problem of gravitational interaction is solved. We also discuss new stabilization mechanism which is based on the use of auxiliary fields.     

Spectral asymmetry of Dirac Hamiltonian in a five-dimensional Kaluza-Klein theory

It is shown that the fermion number in a five-dimensional Kaluza-Klein theory (M⁴×S¹) in which the fermion is interacting with a monopole field, is quantized in units of (ϕR)² where the scalar ϕ is asymptotically constant andR is the radius of S¹.     

Solution of the five-dimensional vacuum Einstein equations in Kaluza-Klein theory

In a recent paper Ross obtained the five-dimensional vacuum Einstein equations in Kaluza-Klein theory with energy-momentum tensor equal to zero and solved the equations for a particular case. Here we obtain the complete set of solutions of these equations.     

五维大反弹宇宙学模型的重建及其相关宇宙学量的演化

在五维大反弹宇宙学模型框架下,通过给定三种不同的暗能量有效态方程,确定了在该模型中起重要作用的函数f(z),从而描述了五维大反弹模型中相关的宇宙学量随红移量z的演化.研究表明,与情形Ⅰ中有效态方程相对应的宇宙学量的演化规律和当前天文观测数据符合最好. 关键词： 大反弹宇宙学模型 暗能量 态方程     

Extra force and extra mass from non-compact Kaluza-Klein theory in a cosmological model

Using the Hamilton-Jacobi formalism, we study extra force and extra mass in a recently introduced non-compact Kaluza-Klein cosmological model. We examine the inertial 4D mass m₀ of the inflaton field on a 4D FRW bulk in two examples. We find that m₀ has a geometrical origin and antigravitational effects on a non-inertial 4D bulk should be a consequence of the motion of the fifth coordinate with respect to the 4D bulk.Received: 1 April 2005, Revised: 13 May 2005, Published online: 28 June 2005PACS: 04.20.Jb, 11.10.Kk, 98.80.Cq