Anisotropic Bianchi Type-II Cosmological Models in Self-Creation Cosmology

Totally anisotropic Bianchi type-II cosmological solutions are presented in Barber's second self-creation theory of gravitation both in vacuum and in the presence of stiff-matter. The corresponding cosmological models have no finite singularity. The stiff-matter model gives essentially an empty universe for large time. Some physical and kinematical properties of the models are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oscillating Universe – An Alternative Approach in Cosmology

A new paradigm in cosmology is presented: A geometrical phase transition from the Minkowski space to an anti-deSitter space at its maximum of extension instead of a big bang with inflation. This scenario implies an open universe with a negative cosmological constant which replaces completely the cold dark matter in galaxy clusters. Baryonic matter and radiation are created from the gravitational field over a very long period of about 30 billion years. The contracting universe runs then after a further period of 13 billion years through a minimum with T _max ≃ 1.8 × 10¹² K and a particle density n _max ≃ 5 × 10³⁸ cm^-3 due to Hagedorn’s theory of a hadron gas. After the run through the minimum the universe expands like a big bang universe and reaches due to the negative cosmological constant after 44 billion years its maximal extension. Then it contracts again, and so on: An open ever-oscillating universe.     

Measuring α in the Early Universe

We update the bounds on a time-varying fine structure constant α at the time of BBN (z∼10¹⁰) and CMB (z∼10³) and present the current CMB constraints on α, through a combined analysis of the BOOMERanG, MAXIMA and DASI datasets. We also present a discussion of the constraints on α coming from large-scale structure observations, focusing in particular on the power spectrum from the 2dF survey. Finally we provide a analysis of the degeneracies between α and the other cosmological parameters and discuss ways to break these with both existing and/or forthcoming data. Our results are consistent with no variation in α from the epoch of recombination to the present day, and restrict any such variation to be less than about 4%.We show that the forthcoming MAP and Planck experiments will be able to break most of the currently existing degeneracies between α and other parameters, and measure α to better than percent accuracy. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Need for Ultraviolet to Understand the Chemical Evolution of the Universe and Cosmology.

We identify an important set of key areas where an advanced observational Ultraviolet capability would have major impact on studies of cosmology and Galaxy formation in the young Universe. Most of these are associated with the Universe at z < 3–4. We address the issues associated with Dark matter evidence in the local Universe and the impact of the Warm-Hot Intergalactic Medium WHIM on the local Baryon count. The motivations to make ultraviolet (UV) studies of supernovae (SNe) are reviewed and discussed in the light of the results obtained so far by means of IUE and HST observations. It appears that UV studies of SNe can, and do lead to fundamental results not only for our understanding of the SN phenomenon, such as the kinematics and the metallicity of the ejecta, but also for exciting new findings in Cosmology, such as the tantalizing evidence for “dark energy” that seems to pervade the Universe and to dominate its energetics. The need for additional and more detailed UV observations is also considered and discussed.Finally we show the enormous importance of the UV for abundance evolution in the Intergalactic Medium (IGM), and the importance of the He II studies to identify re-ionization epochs, which can only be done in the UV.     

Cosmology with Supernovae: The Road from Galactic Supernovae to the edge of the Universe

This review gives an update of the cosmological use of SNe Ia and the progress made in testing their properties from the local universe to high-z. The cosmological road from high-z supernovae down to Galactic SNe Ia is followed in search of the answer to standing questions on their nature and their validity as cosmological indicators.     

Magnetic Monopoles in the Early Universe: Pair Production

Magnetic monopoles and antimonopoles with masses M=10¹⁶ Gev and charges q=68.5e in the early universe are considered. Pair production may occur as a result of their Coulomb interaction. Some conditions for formation of such pairs are discussed. In particular, numerical simulations of three particle collisions are carried out. Probabilities for pair production are found in terms of the N-body problem.     

Higher Dimensional FRW Cosmological Models in Self-Creation Theory

The field equations of Barber's (1982) second self-creation theory of gravitation are solved for 5D Friedmann-Robertson-Walker space time using perfect fluid energy momentum tensor. By assuming an equation of state p= ε ρ, (0 ≤ ε ≤ 1), the solutions of the field equations, in different scenarios, in Barber's second self-creation theory are presented and discussed. Some properties of these models are also discussed.     

The Very Early Universe might not have been Radiation-Dominated

The equation of state of the very early Universe and the formula for the radius, are here evaluated. It is shown that the very early classical Universe might not be radiation-dominated, although we do not exclude the existence of the radiation dominated phase for the early, but not the very early Universe. This revised version was published online in July 2006 with corrections to the Cover Date.     

Micro and Macro Cosmological Model in Barber's Second Self-Creation Theory

A spatially homogeneous anisotropic Bianchi type-I cosmological model in the Barber's second self-creation theory is constructed when the gravitational field is generated by a mixture of micro and macro matter fields represented by meson field and perfect fluid respectively. The physical and geometrical features of the micro and macro cosmological model are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmology in South Africa

This paper reviews research in theoretical cosmology in South Africa, providing an overview of the work that has been done and the groups involved in that work.     

Cosmology in a brane-universe

This contribution presents the cosmological models with extra dimensions that have been recently elaborated, which assume that ordinary matter is confined on a surface, called brane, embedded in a higher dimensional spacetime. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmology after COBE

The measured anisotropies in the temperature of the cosmic microwave background radiation (CMB) by the Cosmic Background Explorer (COBE) are consistent with models of gravitational collapse for the formation of large scale structure in the universe. The amplitude of cosmological fluctuations on the largest scales is fixed by COBE. From COBE's data it is also possible to test for the shape of the primordial spectrum. Statistical tests using COBE's two year data and based on the geometric characteristics of anisotropy spots taking into account cosmic variance and the relevant experimental details indicate that the primordial spectrum has a slope in the rangen = 0.8 – 1.3. Possible identification of hot and cold spots of cosmological origin is also given.Presented at the Fourth United Nations/European Space Agency Workshop on Basic Space Science. Cairo, Egypt, 27 June - 1 July 1994.     

Cosmology of Vacuum

Shortly the vacuum component of the Universe from the geometry point of view and from the point of view of the standard model of physics of elementary particles is discussed. Some arguments are given to the calculated value of the cosmological constant (Zel’dovich’s approximation). A new component of space vacuum (the gravitational vacuum condensate) is involved the production of which has fixed time in our Universe. Also the phenomenon of vacuum selforganization must be included in physical consideration of the Universe evolution.     

Chaos in Relativity and Cosmology

Chaos appears in various problems of Relativity and Cosmology. Here we discuss (a) the Mixmaster Universe model, and (b) the motions around two fixed black holes. (a) The Mixmaster equations have a general solution (i.e. a solution depending on 6 arbitrary constants) of Painlevé type, but there is a second general solution which is not Painlevé. Thus the system does not pass the Painlevé test, and cannot be integrable. The Mixmaster model is not ergodic and does not have any periodic orbits. This is due to the fact that the sum of the three variables of the system (α + β + γ) has only one maximum for τ = τ_m and decreases continuously for larger and for smaller τ. The various Kasner periods increase exponentially for large τ. Thus the Lyapunov Characteristic Number (LCN) is zero. The "finite time LCN" is positive for finite τ and tends to zero when τ → ∞. Chaos is introduced mainly near the maximum of (α + β + γ). No appreciable chaos is introduced at the successive Kasner periods, or eras. We conclude that in the Belinskii-Khalatnikov time, τ, the Mixmaster model has the basic characteristics of a chaotic scattering problem. (b) In the case of two fixed black holes M₁ and M₂ the orbits of photons are separated into three types: orbits falling into M₁ (type I), or M₂ (type II), or escaping to infinity (type III). Chaos appears because between any two orbits of different types there are orbits of the third type. This is a typical chaotic scattering problem. The various types of orbits are separated by orbits asymptotic to 3 simple unstable orbits. In the case of particles of nonzero rest mass we have intervals where some periodic orbits are stable. Near such orbits we have order. The transition from order to chaos is made through an infinite sequence of period doubling bifurcations. The bifurcation ratio is the same as in classical conservative systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

伽玛暴宇宙学的研究

伽玛射线暴(简称伽玛暴,gamma-ray burst (GRB))是一种来自宇宙空间中的伽玛射线波段流量突然增亮的现象,最早由Vela卫星在1967年发现.1997年人们通过余辉测得了伽玛暴的红移,从而确定了其宇宙学的起源.伽玛暴宇宙学包括用长暴的标准烛光关系限制暗能量和宇宙学参数,用长暴研究高红移的恒星形成率,研究金属丰度的演化、尘埃及量子引力等.     

Polarized Radiation in Relativistic Cosmology

A method to solve the general-relativistic equation of radiative transfer for polarized light incorporating elastic COMPTON scattering is discussed. The method is based on an expansion in spin-o and spin-2 spherical harmonics.     

Brans-Dicke Quantum Cosmology

By solving a Wheeler-De Witt ‘extended’ equation in the Brans-Dicke theory, we have found that the probability distribution predicts: i) An initial value for the Brans-Dicke scalar field φ ∼ ρ^1/2_VAC in the beginning of the inflation, where ρ_VAC is the vacuum density energy (this gives a planck mass ∼ ρ^1/4_VAC) ii) Large values for the Brans-Dicke parameter w. On the other hand it is shown that by taking into account the dynamical behaviour of φ and the matter scalar field σ we can formulate a ‘creation boundary condition’ where in the ‘beginning’ of the Universe (R =0, ‘nothing’ for some authors) we have a dynamical σ already ‘created’. This could be the energetic mechanism which makes Universe tunnels the potential barrier to evolve classically after. Besides we have found the possibility of a cosmological uncertainty principle. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmology and Civilizations

The available observational date and cosmological models indicate the possible existence of supercivilizations with ages of technological development 6-8 gigayears larger than on the Earth. The probability of their detection is probably conne with observations at wavelengths from 3 mcm to 3 mm, and also with the solution of the hidden mass problem and searches for multiconnection of the Universe.     

非微扰的极早期宇宙现象学: 共振的原初扰动与非高斯尾巴

在精确宇宙学的时代, 多信使、高精度、小尺度的宇宙学观测在帮助人们从更加深刻的层面理解宇宙极早期的同时, 也给基于线性近似和微扰展开宇宙学扰动理论带来了新的挑战. 近年来, 对原初引力波和原初黑洞的搜寻使得研究人员们对早期宇宙在小尺度上的非线性非微扰过程产生了浓厚的研究兴趣. 综述了在宇宙学小尺度上关于原初黑洞产生以及引力波研究取得的诸多进展, 重点关注了使用Mathieu方程的共振效应来研究小尺度功率谱放大以及诱导产生可观测的原初引力波的方法. 此外, 还尝试探讨了非高斯尾巴对原初黑洞形成的影响. 发现Mathieu方程所具备的共振效应可以提供一种有效的方法来刻画原初宇宙中小尺度的非微扰动力学过程, 从而能够更好地理解原初黑洞的形成以及相关的引力波产生机制. 同时, 非微扰的非高斯性在原初黑洞形成中可能会产生不可忽视的影响.