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1.
Boisseau B Esposito-Farese G Polarski D Starobinsky AA 《Physical review letters》2000,85(11):2236-2239
The present acceleration of the Universe strongly indicated by recent observational data can be modeled in the scope of a scalar-tensor theory of gravity. We show that it is possible to determine the structure of this theory along with the present density of dustlike matter from two observable cosmological functions: the luminosity distance and the linear density perturbation in the dustlike matter component as functions of redshift. Explicit results are presented in the first order in the small inverse Brans-Dicke parameter omega(-1). 相似文献
2.
A new relation for the density parameter Ω is derived as a function of expansion velocity υ based on Carmeli's cosmology.
This density function is used in the luminosity distance relation D
L. A heretofore neglected source luminosity correction factor (1 − (υ/c)2)−1/2 is now included in D
L. These relations are used to fit type Ia supernovae (SNe Ia) data, giving consistent, well-behaved fits over a broad range
of redshift 0.1 < z < 2. The best fit to the data for the local density parameter is Ωm = 0.0401 ± 0.0199. Because Ωm is within the baryonic budget there is no need for any dark matter to account for the SNe Ia redshift luminosity data. From
this local density it is determined that the redshift where the universe expansion transitions from deceleration to acceleration
is z
t = 1.095+0.264
−0.155. Because the fitted data covers the range of the predicted transition redshift z
t, there is no need for any dark energy to account for the expansion rate transition. We conclude that the expansion is now
accelerating and that the transition from a closed to an open universe occurred about 8.54 Gyr ago. 相似文献
3.
Teppo Mattsson 《General Relativity and Gravitation》2010,42(3):567-599
Motivated by the observed cosmic matter distribution, we present the following conjecture: due to the formation of voids and
opaque structures, the average matter density on the path of the light from the well-observed objects changes from Ω
M
≃ 1 in the homogeneous early universe to Ω
M
≃ 0 in the clumpy late universe, so that the average expansion rate increases along our line of sight from EdS expansion
Ht ≃ 2/3 at high redshifts to free expansion Ht ≃ 1 at low redshifts. To calculate the modified observable distance–redshift relations, we introduce a generalized Dyer–Roeder
method that allows for two crucial physical properties of the universe: inhomogeneities in the expansion rate and the growth
of the nonlinear structures. By treating the transition redshift to the void-dominated era as a free parameter, we find a
phenomenological fit to the observations from the CMB anisotropy, the position of the baryon oscillation peak, the magnitude–redshift
relations of type Ia supernovae, the local Hubble flow and the nucleosynthesis, resulting in a concordant model of the universe
with 90% dark matter, 10% baryons, no dark energy, 15 Gyr as the age of the universe and a natural value for the transition
redshift z
0 = 0.35. Unlike a large local void, the model respects the cosmological principle, further offering an explanation for the
late onset of the perceived acceleration as a consequence of the forming nonlinear structures. Additional tests, such as quantitative
predictions for angular deviations due to an anisotropic void distribution and a theoretical derivation of the model, can
vindicate or falsify the interpretation that light propagation in voids is responsible for the perceived acceleration. 相似文献
4.
N. A. Inogamov Yu. V. Petrov S. I. Anisimov A. M. Oparin N. V. Shaposhnikov D. von der Linde J. Meyer-ter-Vehn 《JETP Letters》1999,69(4):310-316
Recent experiments have utilizied high-power subpicosecond laser pulses to effect the ultrafast heating of a condensed material
to temperatures far above the critical temperature. Using optical diagnostics it was established that a complicated density
profile with sharp gradients, differing substantially from an ordinary rarefaction wave, forms in the expanding heated matter.
The present letter is devoted to the analysis of the expansion of matter under the conditions of the experiments reported
by D. von der Linde, K. Sokolowski-Tinten, and J. Bialkowski, Appl. Surf. Science 109/110, 1 (1996); K. Sokolowski-Tinten, J. Bialkowski, A. Cavalleri et al., Proc. Soc. Photo-Opt. Instum. Eng. 3343, 46 (1998); and, K. Sokolowski-Tinten, J. Bialkowski, A. Cavalleri et al., Phys. Rev. Lett. 81, 224 (1998). It is shown that if the unloading adiabat passes through the two-phase region, a thin liquid shell filled with
low-density two-phase matter forms in the expanding material. The shell moves with a constant velocity. The velocity in the
two-phase material is a linear function of the coordinate (flow with uniform deformation), and the density is independent
of the coordinate and decreases with time as t
−1.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 284–289 (25 February 1999) 相似文献
5.
John G. Hartnett 《Foundations of Physics》2006,36(6):839-861
The velocity of the Hubble expansion has been added to General Relativity by Moshe Carmeli and this resulted in new equations of motion for the expanding universe. For the first time the observational magnitude–redshift data derived from the high-z supernova teams has been analysed in the framework of the Carmeli theory and the fit to that theory is achieved without the inclusion of any dark matter. Best fits to the data yield an averaged matter density for the universe at the present epoch Ωm ≈ 0.021, which falls well within the measured values of the baryonic matter density. And the best estimate of ΩΛ+ Ωm ≈ 1.021 at the present epoch. The analysis also clearly distinguishes that the Hubble expansion of the universe is speed-limited. 相似文献
6.
P. Castorina K. Redlich H. Satz 《The European Physical Journal C - Particles and Fields》2009,59(1):67-73
We interpret the phase structure of hadronic matter in terms of the basic dynamical and geometrical features of hadrons. Increasing
the density of constituents of finite spatial extension, by increasing the temperature T or the baryochemical potential μ, eventually “fills the box” and eliminates the physical vacuum. We determine the corresponding transition as a function of
T and μ through percolation theory. At low baryon density, this means a fusion of overlapping mesonic bags to one large bag, while
at high baryon density, hard-core repulsion restricts the spatial mobility of baryons. As a consequence, there are two distinct
limiting regimes for hadronic matter. We compare our results to those from effective chiral model studies. 相似文献
7.
The nature of the dark energy is still a mystery and several models have been proposed to explain it. Here we consider a phenomenological
model for dark energy decay into photons and particles as proposed by Lima (Phys Rev D 54:2571, 1996). He studied the thermodynamic
aspects of decaying dark energy models in particular in the case of a continuous photon creation and/or disruption. Following
his approach, we derive a temperature redshift relation for the cosmic microwave background (CMB) which depends on the effective
equation of state w
eff and on the “adiabatic index” γ. Comparing our relation with the data on the CMB temperature as a function of the redshift obtained from Sunyaev–Zel’dovich
observations and at higher redshift from quasar absorption line spectra, we find w
eff = −0.97 ± 0.03, adopting for the adiabatic index γ = 4/3, in good agreement with current estimates and still compatible with w
eff = −1, implying that the dark energy content being constant in time. 相似文献
8.
The quantum creation of a closed Friedmann universe is studied on the basis of a Wheeler-DeWitt equation with two arguments
— a scale factor and a scalar-field potential. In the quasiclassical approximation the wave function of the universe (WF)
starts to evolve at a zero scalar field. A near-Planckian energy density of the field arises as a result of tunneling through
a potential barrier. In our opinion, this variant of the scenario most closely resembles creation ex nihilo. The only parameter controlling quantum evolution is the mass of a quantum of the scalar field. In the paper by Khalatnikov
and Schiller [JETP Lett. 57,1 (1993)], tunneling through the classically inaccessible region of the superpotential U(a,φ) is calculated by the instanton method. However, this method requires that the potential U(a,φ) satisfy special conditions in the space (a,φ). For this reason, in the present paper the tunneling calculation is performed by the method of characteristics for the
quasiclassical approximation of the Wheeler-DeWitt equation under the barrier. The WKB theory, which has been well-developed
for one-dimensional problems, is employed along each characteristic. It is shown that the corresponding turning points are
also points where U(a, φ)=0. The total barrier penetrability is obtained by averaging over a bundle of characteristics.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 305–308 (10 September 1996) 相似文献
9.
In this paper, we consider a class of five-dimensional Ricci-flat vacuum solutions, which contain two arbitrary functions μ(t) and ν(t). It is shown that μ(t) can be rewritten as a new arbitrary function f(z) in terms of redshift z and the f(z) can be determined by choosing particular deceleration parameters q(z) which gives early deceleration and late time acceleration. In this way, the 5D cosmological model can be reconstructed and the evolution of the universe can be determined.
PACS: 04.50.+h, 98.80.-k 相似文献
10.
Vinod B Johri 《Pramana》2002,59(3):L553-L561
We present a realistic scenario of tracking of scalar fields with varying equation of state. The astrophysical constraints
on the evolution of scalar fields in the physical universe are discussed. The nucleosynthesis and the galaxy formation constraints
have been used to put limits on Ωφ and estimate ɛ during cosmic evolution. Interpolation techniques have been applied to estimate ɛ ⋍0.772 at the present epoch.
The epoch of transition from matter to quintessence dominated era and consequent onset of acceleration in cosmic expansion
is calculated and taking the lower limit Θ
n
/0
=0.2 as estimated from SN
e
I
a
data, it is shown that the supernova observations beyond redshift z=1 would reveal deceleration in cosmic expansion. 相似文献
11.
In the Friedmann cosmology, the deceleration of the expansion q plays a fundamental role. We derive the deceleration as a function of redshift q(z) in two scenarios: ΛCDM model and modified Chaplygin gas (MCG) model. The function for the MCG model is then fitted to the cosmological data in
order to obtain the cosmological parameters that minimize χ
2. We use the Fisher matrix to construct the covariance matrix of our parameters and reconstruct the q(z) function. We use Supernovae Ia, WMAP5, and BAO measurements to obtain the observational constraints. We determined the present
acceleration as q
0 = − 0.65 ±0.19 for the MCG model using the Union2 dataset of SNeIa, BAO, and CMB and q
0 = − 0.67 ±0.17 for the Constitution dataset, BAO and CMB. The transition redshift from deceleration to acceleration was found
to be around 0.80 for both datasets. We have also determined the dark energy parameter for the MCG model: Ω
X0 = 0.81 ±0.03 for the Union2 dataset and Ω
X0 = 0.83 ±0.03 using the Constitution dataset. 相似文献
12.
We have examined a solution to the FRW model of the Einstein and de Sitter Universe, often termed the standard model of cosmology, using wide values for the normalized cosmic constant (Ω∧) and spacetime curvature (Ω
k
) with proposed values of normalized matter density. These solutions were evaluated using a combination of the third type of elliptical equations and were found to display critical points for redshift z, between 1 and 3, when Ω∧ is positive. These critical points occur at values for normalized cosmic constant higher than those currently thought important, though we find this solution interesting because the Ω∧ term may increase in dominance as the Universe evolves bringing this discontinuity into importance. We also find positive Ω∧tends towards attractive at values of z which are commonly observed for distant galaxies. 相似文献
13.
Muhittin Mungan 《Journal of statistical physics》2007,126(1):207-242
14.
We present the scalar-tensor gravitational theory with an exponential potential in which Pauli metric is regarded as the physical
space-time metric. We show that it is essentially equivalent to coupled quintessence (CQ) model. However for baryotropic fluid
being radiation there are in fact no coupling between dilatonic scalar field and radiation. We present the critical points
for baryotropic fluid and investigate the properties of critical points when the baryotropic matter is specified to ordinary
matter. It is possible for all the critical points to be attractors as long as the parameters λ and β satisfy certain conditions. To demonstrate the attractor behaviors of these critical points, We numerically plot the phase
plane for each critical point. Finally with the bound on β from the observation and the fact that our universe is undergoing an accelerating expansion, we conclude that present accelerating
expansion is not the eventual stage of universe. Moreover, we numerically describe the evolution of the density parameters
Ω and the decelerating factor q, and computer the present values of some cosmological parameters, which are consistent with current observational data. 相似文献
15.
Varun Sahni 《Pramana》1999,53(6):937-944
I briefly review the observational evidence for a small cosmological constant at the present epoch. This evidence mainly comes
from high redshift observations of Type 1a supernovae, which, when combined with CMB observations strongly support a flat
Universe with Ω
m
+ ΩA ⋍ 1. Theoretically a cosmological constant can arise from zero point vacuum fluctuations. In addition ultra-light scalar
fields could also give rise to a Universe which is accelerating driven by a time dependent Λ-term induced by the scalar field
potential. Finally a Λ dominated Universe also finds support from observations of galaxy clustering and the age of the Universe. 相似文献
16.
17.
S. Hands P. Kenny S. Kim J. -I. Skullerud 《The European Physical Journal A - Hadrons and Nuclei》2011,47(5):60
We present results from a simulation of SU(2) lattice gauge theory with N
f
= 4 flavors of Wilson fermion and non-zero quark chemical potential μ, using the same 123×24 lattice, bare gauge coupling, and pion mass in cut-off units as a previous study (S. Hands, S. Kim, J.I. Skullerud, Phys.
Rev. D 81, 091502(R) (2010)) with N
f
= 2 . The string tension for N
f
= 4 is found to be considerably smaller implying smoother gauge field configurations. Thermodynamic observables and order
parameters for superfluidity and color deconfinement are studied, and comparisons drawn between the two theories. Results
for quark density and pressure as functions of μ are qualitatively similar for N
f
= 2 and N
f
= 4 ; in both cases there is evidence for a phase in which baryonic matter is simultaneously degenerate and confined. Results
for the stress-energy tensor, however, suggest that while N
f
= 2 has a regime where dilute matter is non-relativistic and weakly interacting, N
f
= 4 matter is relativistic and strongly interacting for all values of μ above onset. 相似文献
18.
A set of density dependent nucleon-nucleon (N-N) interactions has been examined in nuclear matter calculations by varying
spin-isospin contributions. Two sets of potentials have been considered. One having a density dependentσ-function type short range part followed by one term long range Gaussian part while the other having a density dependentσ-function part followed by two Gaussian terms. The strength parameters of the potential have been fitted to the saturation
properties of nuclear matter, i.e. binding energy per particle of 15.5 MeV atk
F=1.35 fm−1. Several sets of these two potentials have been generated by varying the strength parameterM of Majorana exchange operatorP
M. It is seen thatM indirectly controls the spin, iso-spin contribution to the interaction potential and thus affects the nuclear matter properties
such as compressibility and symmetry energy considerably, while variation of these quantities with the range parameterμ for givenM is moderate at lowM values while at higherM values it is quite large. 相似文献
19.
John G. Hartnett 《Foundations of Physics》2008,38(3):201-215
The redshift-distance modulus relation, the Hubble Diagram, derived from Cosmological General Relativity has been extended
to arbitrarily large redshifts. Numerical methods were employed and a density function was found that results in a valid solution
of the field equations at all redshifts. The extension has been compared to 302 type Ia supernova data as well as to 69 Gamma-ray
burst data. The latter however do not truly represent a ‘standard candle’ as the derived distance moduli are not independent
of the cosmology used. Nevertheless the analysis shows a good fit can be achieved without the need to assume the existence
of dark matter.
The Carmelian theory is also shown to describe a universe that is always spatially flat. This results from the underlying
assumption of the energy density of a cosmological constant ΩΛ=1, the result of vacuum energy. The curvature of the universe is described by a spacevelocity metric where the energy content of the curvature at any epoch is Ω
K
=ΩΛ−Ω=1−Ω, where Ω is the matter density of the universe. Hence the total density is always Ω
K
+Ω=1. 相似文献
20.
Many structures in nature are invariant under the transformation pair, (p,r)→(b
r,−p/b), where b is some scale factor. Born’s reciprocity hypothesis affirms that this invariance extends to the entire Hamiltonian and equations
of motion. We investigate this idea for atomic physics and galactic motion, where one is basically dealing with a 1/r potential and the observations are very accurate, so as to determine the scale b≡mΩ. We find that an Ω∼1.5×10−15 s−1 has essentially no effect on atomic physics but might possibly offer an explanation for galactic rotation, without invoking
dark matter. 相似文献