共查询到20条相似文献,搜索用时 15 毫秒
1.
Marek Biesiada 《Astrophysics and Space Science》2003,283(4):511-516
Theory of dynamical systems offers a possibility of investigating the space of all possible solutions. In the context of simple
cosmological models such like Varying Speed of Light Friedman-Robertson-Walker (VSL FRW) models there exists a systematic
method of reducing field equations to certain two-dimensional dynamical system. One of the features of this reduction is the
possibility of representing the model as a Hamiltonian system in which the properties of the potential function V(X) can serve as a tool for qualitative classification of possible evolutions of a(t). Some important features like resolution of the flatness problem, existence of event horizons near the singularity can be
visualized as domains on the phase-space. Then one is able to see how large is the class of solutions (labelled by the initial
conditions) leading to the desired property.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
We report results on the construction of cosmological braneworld models in the context of the Einstein-Gauss-Bonnet gravity,
which include the leading correction to the Einstein-Hilbert action suggested by superstring theory. We obtain and study the
equations governing the dynamics of the standard cosmological models. We find that they can be written in the same form as
in the case of the Randall-Sundrum model but with time-varying four-dimensional gravitational and cosmological constants.
Finally, we discuss the cosmological evolution predicted by these models and their compatibility with observational data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Malcolm Fairbairn 《Astrophysics and Space Science》2003,283(4):613-618
Precision measurements of gauge couplings at particle accelerators strongly suggest that the standard model fields are unified
at about 1016 GeV. This talk will consist of a brief review of this evidence and also how in such a setting variations in α
em
lead to much larger variations in Λ
QCD
. I will then describe how variations in the strong force will impact upon nuclear astrophysics, considering in particular
the stability of di-nucleons and stellar and primordial nucleosynthesis. (Based upon collaborations with T. Dent and with
A. Csoto, H. Oberhummer and H. Schlattl.)
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Ph. Brax C. van de Bruck A.-C. Davis C.S. Rhodes 《Astrophysics and Space Science》2003,283(4):627-632
Higher-dimensional theories imply that some constants, such as the gravitational constant and the strength of the gauge-couplings,
are not fundamental constants. Instead they are related to the sizes of the extra-dimensional space, which are moduli fields
in the four-dimensional effective theory. We study the cosmological evolution of the moduli fields appearing in brane world
scenarios and discuss the implications for varying constants.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
J. A. Belinchón 《Astrophysics and Space Science》2006,302(1-4):161-170
It is investigated the behaviour of the “constants” G, c and Λ in the framework of a perfect fluid LRS Bianchi I cosmological model. It has been taken into account the effects of
a c-variable into the curvature tensor. Two exact cosmological solutions are investigated, arriving t the conclusion that if
q < 0 (deceleration parameter) then G, c are growing functions on time t while Λ is a negative decreasing function on time. 相似文献
6.
In this paper we study the evolution of a LRS Bianchi I Universe, filled with a bulk viscous cosmological fluid in the presence
of time varying constants “but” taking into account the effects of a c-variable into the curvature tensor. We find that the only physical models are those which “constants” G and c are growing functions on time t, while the cosmological constant Λ is a negative decreasing function. In such solutions the energy density obeys the ultrastiff
matter equation of state i.e. ω = 1. 相似文献
7.
Arthur Kosowsky 《New Astronomy Reviews》2003,47(11-12):939
The proposed Atacama Cosmology Telescope (ACT) project is described. This multi-institution collaboration aims to produce arcminute-resolution and micro-Kelvin sensitivity maps of the microwave background temperature over 200 square degree of the sky in three frequency bands. We give a brief overview of the scientific motivations for such a map, followed by a design outline of our 6-m custom telescope, an overview of our proposed bolometer array detector technology, and site considerations and scan strategy. We also describe associated optical and X-ray galaxy cluster surveys. 相似文献
8.
在Friedmann建立膨胀宇宙模型和Hubble发现膨胀迹象后,宇宙均匀性的假设得到证实是重要的进展,但是此后,由于Hubble常数,宇宙密度和真空能密度未被可靠地确定,宇宙理论尚难以有认真的定量检验,近两年里,这些基本参量的测定有了突破性的进展,它标志着宇宙学理论将在今后一十年内走向成熟。 相似文献
9.
N.S. Kardashev 《Astrophysics and Space Science》1997,252(1-2):25-40
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. 相似文献
10.
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. 相似文献
11.
《New Astronomy Reviews》2002,46(11):645-657
The major thrust of present day scientific cosmology is that of examining the effect of local physical laws on the large-scale structure of the cosmos. However there has also from the earliest times been a counter theme: the study of the way that global properties of the universe can influence its local properties. The purpose of the present paper is to revisit this topic. 相似文献
12.
Satio Hayakawa 《Astrophysics and Space Science》1989,160(1-2):7-17
Assuming a large collecting area, a good angular resolution and a large field of view expected for the Japanese National Large Telescope (JNLT), we demonstrate that JNLT will provide a useful means of studying cosmological objects of interest. Among them I discuss how cosmological parameters and evolutionary effects can be obtained from redshift-magnitude relations, galaxy counts, distant supernovae, quasar properties, and large-scale structures. An advantage of near infrared observations is emphasized.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
13.
G. Contopoulos N. Voglis C. Efthymiopoulos 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):1-16
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 = τm 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. 相似文献
14.
A non-linear gravitational model with a multidimensional geometry and quadratic scalar curvature is considered. For certain
parameter ranges, the extra dimensions are stabilized if the internal spaces have negative constant curvature. As a consequence,
the 4-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. The homogeneous
and isotropic external space is asymptotically AdS4. The connection between the D-dimensional and the 4-dimensional fundamental mass scales sets an additional restriction on
the parameters of the considered non-linear models.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Miloslav Dubec 《Astrophysics and Space Science》1991,175(2):207-213
A theory of gravitation in a flat space is briefly described, which gives a completely new view on cosmological problems. Instead of expansion of the Universe, a contraction of bodies and clusters is obtained. This theory excludes the closed solutions as non-physical ones and gives a simple condition for the stability of gravitationally-bounded systems with respect to cosmological gravitational field. 相似文献
16.
17.
现代科学表明宇宙中99%以上的可观测物质都处于等离子体状态,从小尺度的微观粒子动力学集体过程与能量转换机制到大尺度的宇宙等离子天体结构状态与爆发活动现象,都是等离子天体物理学的研究课题.从宇宙演化历史、大尺度结构形成以及爆发活动现象等方面,系统地论述了等离子天体物理学在现代天文学发展以及现代等离子体宇宙观形成中的重要作用.同时,结合空间卫星科学探测研究及其对现代天文学的巨大影响,进一步阐述了地球磁层和日球层等空间等离子体实地探测研究在等离子天体物理学研究中所扮演的“天然实验室”的独特作用. 相似文献
18.
对IAU1976天文常数系统中的基础常数的测定方法进行了评述,指出十个基础常数已发生了许多变化,光速已成为常数,地球赤道半径可用于大地水准面的重力势代替,黄经总岁差需进行修改,章动常数已不能称为基础常数,其它常数也都有了新的测定结果,IAU1976天文常数系统已跟上不天文学的发展,并存在很大的缺陷,必须进行修订和改进,天文常数的测定方法和理论研究都在迅速发展之中,我们应当关心这个领域的研究。 相似文献
19.
Reuven Opher 《Astrophysics and Space Science》1997,256(1-2):37-50
We discuss some of the major areas in astronomy and cosmology where plasma physics is important: (1) origin of stars; (2) distortions of the microwave background radiation; (3) expansion rate of the Early Universe; (4) the magnetic fields and relativistic electrons in jets; (5) the collimation of jets; (6) the origin of stellar winds; (7) the origin of filaments and clouds not gravitationally bound; and (8) the origin of cosmic rays. 相似文献
20.
M.J. Rees 《Astrophysics and Space Science》2003,285(2):375-388
Fred Hoyle famously drew attention to the significance of apparent coincidences in the energy levels of the carbon and oxygen
nucleus. This paper addresses the possible implications of other coincidences in cosmology.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献