共查询到20条相似文献，搜索用时 502 毫秒
1.
The possibility of using a trap with ultracold neutrons as a detector of dark matter particles with long-range forces is considered.
The main advantage of the proposed method lies in the possibility of detecting a recoil energy of ∼10−7 eV. Constraints on the parameters of an interaction potential of the form φ (r) = ae
−r/b
/r between dark matter particles and a neutron are presented at various dark matter densities on Earth. The assumption about
the long-range interaction of dark matter particles and ordinary matter is shown to lead to a significant increase in the
elastic scattering cross section at low energies. As a consequence, it becomes possible to capture and accumulate dark matter
in the Earth’s gravitational field. The accumulated dark matter in the Earth’s gravitational field is roughly estimated. The
first experimental constraints on the existence of dark matter with long-range forces on Earth are presented. 相似文献
2.
3.
4.
In this paper we study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic
FRW universe filled with barotropic fluid and dark energy. The scale factor is considered as a power law function of time
which yields a constant deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect
fluid as well as direct interaction with it. The cosmic jerk parameter in our derived models is consistent with the recent
data of astrophysical observations. It is concluded that in non-interacting case, all the three open, close and flat universes
cross the phantom region whereas in interacting case only open and flat universes cross the phantom region. We find that during
the evolution of the universe, the equation of state (EoS) for dark energy ω
D
changes from ω
D
>−1 to ω
D
<−1, which is consistent with recent observations. 相似文献
5.
Applying the parametrization of dark energy density, we can construct directly independent-model potentials. In Born-Infeld
type phantom dark energy model, we consider four special parametrization equation of state parameter. The evolutive behavior
of dark energy density with respect to red-shift z, potentials with respect to φ and z are shown mathematically. Moreover, we investigate the effect of parameter η upon the evolution of the constructed potential with respect to z. These results show that the evolutive behavior of constructed Born-Infeld type dark energy model is quite different from
those of the other models. 相似文献
6.
S. D. Katore K. S. Adhav A. Y. Shaikh M. M. Sancheti 《Astrophysics and Space Science》2011,333(1):333-341
We consider a self-consistent system of Plane symmetric cosmology and binary mixture of perfect fluid and dark energy. The
perfect fluid is taken to be one obeying the usual equation of state p=γρ with γ∈[0,1]. The dark energy is considered to be either the quintessence or Chaplygin gas. Exact solutions to the corresponding
Einstein’s field equations are obtained as a quadrature. The cases of Zeldovich Universe, Dust Universe and Radiation Universe
and models with power-law and exponential expansion have discussed in detail. For large t, the models tend to be isotropic. 相似文献
7.
M. R. Setare 《Astrophysics and Space Science》2010,326(1):27-31
In this paper, we study a cosmological application of the new agegraphic dark energy density in the f(R) gravity framework. We employ the new agegraphic model of dark energy to obtain the equation of state for the new agegraphic
energy density in a spatially flat universe. Our calculations show, taking n<0, that it is possible to have w
Λ crossing −1. This implies that one can generate a phantom-like equation of state from a new agegraphic dark energy model
in a flat universe in the modified gravity cosmology framework. Also, we develop a reconstruction scheme for the modified
gravity with f(R) action. 相似文献
8.
We consider a self consistent system of Bianchi Type-I cosmology and Binary Mixture of perfect fluid and dark energy. The
perfect fluid is taken to be obeying equations of state p
PF
=γρ
PF
with γ∈[0,1]. The dark energy is considered to be obeying a quintessence-like equation of state where the dark energy obeys equation
of state p
DE
=ωρ
DE
where ω∈[−1,0]. Exact solutions to the corresponding Einstein field equations are obtained. Some special cases are discussed and
studied. Further more power law models and exponential models are investigated. 相似文献
9.
The present study deals with spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological
model with dominance of dark energy. To get the deterministic model of Universe, we assume that the shear scalar (σ) in the model is proportional to expansion scalar (θ). This condition leads to A=B
n
, where A, B are metric potential and n is positive constant. It has been found that the anisotropic distribution of dark energy leads to the present accelerated
expansion of Universe. The physical behavior of the Universe has been discussed in detail. 相似文献
10.
We explore the predictions of a class of dark energy models, quinstant dark energy, concerning the structure formation in
the Universe, both in the linear and non-linear regimes. Quinstant dark energy is considered to be formed by quintessence and a negative cosmological constant. We conclude that these models give good predictions for structure formation in the linear regime, but fail to do so in the
non-linear one, for redshifts larger than one. 相似文献
11.
R. Stephen White 《Astrophysics and Space Science》1996,240(1):75-87
Some requirements are discussed for solid hydrogen formation in cold dark dense clouds in galaxies. If temperatures in the clouds are near the microwave background temperature of 2.7 K and molecular hydrogen densities are 3×105 cm–3 or higher, as suggested by recent observations, it may be possible for solid hydrogen objects to form. Comet size hydrogen solids could build from molecular hydrogen condensation on grains and by collisions. Heated primarily by cosmic rays, objects with 100 km radii could last billions of years. The larger objects may be detectable, in the future, by sensitive gravitational lensing or eclipsing observations. Other possibilities are discussed for future detection of the cold dark dense molecular hydrogen regions. In our model, helium is added along with the hydrogen to preserve the primordial helium to hydrogen mass ratio,Y
p
, of the standard model. In the hot regions of the universe the solid hydrogen objects sublime and melt so our model predictsY
p
=0.250, the same as other baryonic dark matter models with identical values of =0.1,H
o
=50 and =6.8×10–10. This value cannot be ruled out at present because of the large systematic uncertainties in the observed value of 0.232. In the cold dark regions where solid hydrogen objects exist, we predict thatY
p
will be greater than 0.250. Observations are not yet sensitive enough to measure this ratio. 相似文献
12.
We study the holographic dark energy on the subject of Hořava-Lifshitz gravity with a time dependent gravitational constant
G(t), in the non-flat space-time. We obtain the differential equation that specify the evolution of the dark energy density parameter
based on varying gravitational constant. We find out a relation for the state parameter of the dark energy equation of state
to low red-shifts which containing varying G corrections in the non-flat space-time. 相似文献
13.
SeveralN-body experiments were performed in order to simulate the dynamical behaviour of systems of galaxies gravitationally dominated by a massive dark background.We discuss mass estimates from the dynamics of the luminous component (M
VT) under the influence of such a background, assuming a constant dark/luminous mass ratio (M
D/M
L) and plausible physical conditions. We extend in this way previous studies (Smith, 1980, 1984) about the dependence ofM
VT on the relative distributions of dark and luminous matter (Limber, 1959). We found that the observed ratio of the virial theorem mass to luminosity (M
VT/L) in systems of galaxies of different sizes could be the result of different stages of their post-virialisation evolution as was previously suggested by White and Rees (1978) and Barnes (1983). This evolution is mainly the result of the dynamical friction that dark matter exerts on the luminous component. Thus our results give support to the idea that compact groups of galaxies are dynamically more evolved than large clusters, which is expected from the hierarchical clustering picture for the formation of such structures. 相似文献
14.
We discuss the f(R) gravity model in which the origin of dark energy is identified as a modification of gravity. The Noether symmetry with gauge
term is investigated for the f(R) cosmological model. By utilization of the Noether Gauge Symmetry (NGS) approach, we obtain two exact forms f(R) for which such symmetries exist. Further it is shown that these forms of f(R) are stable. 相似文献
15.
O. Sergijenko Yu. Kulinich B. Novosyadlyj V. Pelykh 《Kinematics and Physics of Celestial Bodies》2009,25(1):17-27
The evolution of scalar perturbations is studied for 2-component (non-relativistic matter and dark energy) cosmological models
at the linear and non-linear stages. The dark energy is assumed to be the scalar field with either classical or tachyonic
Lagrangian and constant equation-of-state parameter w. The fields and potentials were reconstructed for the set of cosmological parameters derived from observations. The comparison
of the calculated within these models and observational large-scale structure characteristics is made. It is shown that for
w = const such analysis can’t remove the existing degeneracy of the dark energy models.
The article is published in the original. 相似文献
16.
K. Karami M. Jamil M. Roos S. Ghaffari A. Abdolmaleki 《Astrophysics and Space Science》2012,340(1):175-184
We study the entropy-corrected version of the new agegraphic dark energy (NADE) model and dark matter in a spatially non-flat Universe and in the framework of Hořava-Lifshitz cosmology. For the two cases containing noninteracting and interacting entropy-corrected NADE (ECNADE) models, we derive the exact differential equation that determines the evolution of the ECNADE density parameter. Also the deceleration parameter is obtained. Furthermore, using a parametrization of the equation of state parameter of the ECNADE model as ω Λ(z)=ω 0+ω 1 z, we obtain both ω 0 and ω 1. We find that in the presence of interaction, the equation of state parameter ω 0 of this model can cross the phantom divide line which is compatible with the observation. 相似文献
17.
Using near-simultaneous full disk solar X-ray images and Hei 10830 spectroheliograms from three rocket flights, we compare dark points identified on the Hei maps with X-ray bright points identified on the X-ray images. We find that for the largest and most obvious features there is a strong correlation: most Hei dark points correspond to X-ray bright points. However, about two-thirds of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced Hei absorption which, however, would not a priori have been selected as a dark point. Therefore, the Hei dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. Hei dark points do, however, identify the locations of the stronger X-ray bright points.Visitor, National Solar Observatory. National Optical Astronomy Observatories operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation. 相似文献
18.
Kantowski-Sachs cosmological model in the presence of magnetized anisotropic dark energy is investigated. The energy-momentum
tensor consists of anisotropic fluid with anisotropic EoS p=ωρ and a uniform magnetic field of energy density ρ
B
. We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar.
The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as
anisotropic fluid does not approach isotropy through the evolution of the universe. 相似文献
19.
A new dark energy model in anisotropic Bianchi type-III space-time with variable equation of state (EoS) parameter has been
investigated in the present paper. To get the deterministic model, we consider that the expansion θ in the model is proportional to the eigen value s2 2\sigma^{2}_{~2} of the shear tensor sj i\sigma^{j}_{~i}. The EoS parameter ω is found to be time dependent and its existing range for this model is in good agreement with the recent observations of
SNe Ia data (Knop et al. in Astrophys. J. 598:102, 2003) and SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004). It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise
due to the contribution to the vacuum energy of the EoS in a time dependent background. Some physical aspects of dark energy
model are also discussed. 相似文献
20.
J. Zhang D. B. Williams J. I. Goldstein R. S. Clarke 《Meteoritics & planetary science》1990,25(3):167-175
Abstract— Characterization of the microstructural features of the metal of the Santa Catharina meteorite was performed using a variety of electron optical techniques. Sample USNM#6293 is chemically homogeneous on the micron scale and has a Ni content of 28.2 wt.%. Its microstructure is similar to that of the Twin City ataxite and contains clear taenite II, i.e., fcc taenite with domains of tetrataenite, < 10 nm in size. Sample USNM#3043 is a more typical Santa Catharina specimen with dark and light regions as observed with the light optical microscope. The dark regions are inhomogeneous and contain 45–50 wt.% Ni and 7–12 wt.% O. The light regions are homogeneous and contain 35 wt.% Ni and no detectable oxygen. The microstructure is that of cloudy zone, i.e., islands of tetrataenite, ～20 nm in size, in a honeycomb matrix. The honeycomb phase contains Ni rich oxide in the dark regions and contains metal, fcc taenite, in the light regions. The original metal structure of USNM#3043 is cloudy zone which formed during cooling into the low temperature miscibility gap of the Fe-Ni phase diagram. The dark regions were developed from the metal by selective corrosion of the honeycomb structure, transforming it into Ni containing oxides, possibly non-stoichiometric Fe2NiO4 while retaining the tetrataenite islands. Using the results of this study, many of the existing discrepancies concerning the microstructure of Santa Catharina can be explained. 相似文献