排序方式: 共有146条查询结果,搜索用时 15 毫秒
1.
Jeff Kanipe 《Astrophysics and Space Science》1995,227(1-2):109-118
Is the big bang model of the universe ascendant and unshakable, or declining and outdated? This paper cursorily explores the state of cosmology today. 相似文献
2.
The evolution of a homogeneous, isotropic cosmological model driven by a nonminimally coupled scalar field is studied. The
potential for the quintessential inflation model proposed by Peebles and Vilenkin is selected as a scalar potential. Possible
scenarios for the cosmological dynamics are described in the conformal Einstein and Jordan representations. It is shown that,
unlike in models with a minimal scalar field, here a class of solutions exists for which the scalar field is fixed at finite
values during cosmological expansion.
__________
Translated from Astrofizika, Vol. 49, No. 3, pp. 487–498 (August 2006). 相似文献
3.
Eric J. Lerner 《Astrophysics and Space Science》1995,227(1-2):145-149
Supporters of the standard Big Bang theory point to the abundances of light elements, predicted by Big Bang Nucleosynthesis (BBN) as one of the main observational supports of the theory. However, current data no longer confirm BBN. Instead, measurements of the abundances of He3, He4, and D clearly contradict BBN at more than a 3 level, eliminating a key support of the Big Bang. 相似文献
4.
The model proposed originally by Mannheim and Kazanas for fitting the shapes of galactic rotation curves has recently been considered by Grumiller to describe gravity of a central object at large distances. Herein we employ the same geometry within the context of nonlinear electrodynamics (NED). Pure electrical NED model is shown to generate the novel Rindler acceleration term in the metric which explains anomalous behaviors of test particles/satellites. Remarkably a pure magnetic model of NED yields flat rotation curves that may account for the missing dark matter. Weak and strong energy conditions are satisfied in such models of NED. 相似文献
5.
Though entropy production is forbidden in standard FRW Cosmology, Berman and Som presented a simple inflationary model where
entropy production by bulk viscosity, during standard inflation without ad hoc pressure terms can be accommodated with Robertson–Walker’s
metric, so the requirement that the early Universe be anisotropic is not essential in order to have entropy growth during
inflationary phase, as we show. Entropy also grows due to shear viscosity, for the anisotropic case. The intrinsically inflationary
metric that we propose can be thought of as defining a polarized vacuum, and leads directly to the desired effects without
the need of introducing extra pressure terms. 相似文献
6.
Jayant V. Narlikar Geoffrey Burbidge R. G. Vishwakarma 《Journal of Astrophysics and Astronomy》2007,28(2-3):67-99
In this paper we discuss the properties of the quasi-steady state cosmological model (QSSC) developed in 1993 in its role
as a cyclic model of the universe driven by a negative energy scalar field. We discuss the origin of such a scalar field in
the primary creation process first described by F. Hoyle & J. V. Narlikar forty years ago. It is shown that the creation processes
which take place in the nuclei of galaxies are closely linked to the high energy and explosive phenomena, which are commonly
observed in galaxies at all redshifts.
The cyclic nature of the universe provides a natural link between the places of origin of the microwave background radiation
(arising in hydrogen burning in stars), and the origin of the lightest nuclei (H, D, He3 and He4). It also allows us to relate the large scale cyclic properties of the universe to events taking place in the nuclei of galaxies.
Observational evidence shows that ejection of matter and energy from these centers in the form of compact objects, gas and
relativistic particles is responsible for the population of quasi-stellar objects (QSOs) and gamma-ray burst sources in the
universe.
In the later parts of the paper we briefly discuss the major unsolved problems of this integrated cosmological and cosmogonical
scheme — the understanding of the origin of the intrinsic redshifts, and the periodicities in the redshift distribution of
the QSOs. 相似文献
7.
G. S. Khadekar Vaishali Kamdi Anirudh Pradhan Saeed Otarod 《Astrophysics and Space Science》2007,310(1-2):141-147
We assume the four dimensional induced matter of the 5D Ricci flat bouncing cosmological solution contains a perfect fluid.
The big bounce singularity of simple 5D cosmological model is studied with the cosmological term Λ=α
ρ and Λ=β
H
2 where α and β are constants and ρ and H are respectively energy density and Hubble parameter. This big bounce singularity is found to be an event horizon at which
the scale factor and mass density of the universe are finite, while the pressure is infinite.
相似文献
8.
K.N. AbazajianE. Calabrese A. CoorayF. De Bernardis S. Dodelson A. FriedlandG.M. Fuller S. HannestadB.G. Keating E.V. Linder C. LunardiniA. Melchiorri R. Miquel E. PierpaoliJ. Pritchard P. SerraM. Takada Y.Y.Y. Wong 《Astroparticle Physics》2011,35(4):177-184
Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach. 相似文献
9.
A. S. Al-Rawaf 《Astrophysics and Space Science》2007,310(1-2):173-175
Due to the recent all-sky, high-precision measurement of microwave background anisotropies by WMAP, a value for baryon-to-photon
ratio η was obtained. At the WMAP value for η, the 4HE abundance was predicted. In this article we use a simple semi-analytical method with 4He predicted and measured values to place a limit on the variation of the gravitational constant G. We find using a conservative range for the measured values for Y
p
, that ΔG/G is constrained between −0.26 and 0.15. If we assume a monotonic power law time dependence G∼t
−β
then β values is constrained between −0.008 and 0.0038, which translate into
. This compares well with results obtained by others using full numerical analysis.
相似文献
10.
H.K. Eriksen C. Dickinson C.R. Lawrence C. Baccigalupi A.J. Banday K.M. Grski F.K. Hansen E. Pierpaoli M.D. Seiffert 《New Astronomy Reviews》2006,50(11-12):861
The quality of CMB observations has improved dramatically in the last few years, and will continue to do so in the coming decade. Over a wide range of angular scales, the uncertainty due to instrumental noise is now small compared to the cosmic variance. One may claim with some justification that we have entered the era of precision CMB cosmology. However, some caution is still warranted: The errors due to residual foreground contamination in the CMB power spectrum and cosmological parameters remain largely unquantified, and the effect of these errors on important cosmological parameters such as the optical depth τ and spectral index ns is not obvious. A major goal for current CMB analysis efforts must therefore be to develop methods that allow us to propagate such uncertainties from the raw data through to the final products. Here we review a recently proposed method that may be a first step towards that goal. 相似文献