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1.
We consider a recently proposed scenario for the generation of primordial cosmological perturbations, the so called Cosmological
Slingshot scenario. We first obtain a general expression for the Slingshot primordial power spectrum which extends previous
results by including a blue pre-bounce residual contribution at large scales. Starting from this expression we numerically
compute the CMB temperature and polarization power spectra arising from the Slingshot scenario and show that they excellently
match the standard WMAP 3-year best-fit results. In particular, if the residual blue spectrum is far above the largest WMAP
observed scale, the Slingshot primordial spectrum fits the data well by only fixing its amplitude and spectral index at the
pivot scale k
p = 10−3
h Mpc−1. We finally show that all possible distinctive Slingshot signatures in the CMB power spectra are confined to very low multipoles
and thus very hard to detect due to large cosmic variance dominated error bars at these scales. 相似文献
2.
F. Atrio-Barandela J. Einasto S. Gottlöber V. Müller A. Starobinsky 《JETP Letters》1997,66(6):397-403
We calculate the temperature anisotropies of the cosmic microwave background (CMB) for several initial power spectra of density
perturbations with a built-in scale suggested by recent optical data on the spatial distribution of rich clusters of galaxies.
Using cosmological models with different values of the spectral index, baryon fraction, Hubble constant, and cosmological
constant, we compare the calculated radiation power spectrum with the CMB temperature anisotropies measured by the Saskatoon
experiment. We show that spectra with a spike at 120h
−1 Mpc are in agreement with the Saskatoon data. The combined evidence from cluster and CMB data favors the presence of a peak
and a subsequent break in the initial matter power spectrum. Such a feature is similar to the prediction of an inflationary
model wherein an inflaton field is evolving through a kink in the potential.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 373–378 (25 September 1997)
Published in English in the original Russian journal. Edited by Steve Torstveit. 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.
P. De Bernardis E. Aquilini A. Boscaleri M. De Petris M. Gervasi L. Martinis S. Masi V. Natale P. Palumbo F. Scaramuzzi 《Il Nuovo Cimento C》1993,16(6):721-726
Summary We describe a balloon-borne telescope, optimized for observations of the Cosmic Microwave Background (CMB) anisotropies in
the mm wavelength region, at angular scales around 10. We stress the scientific motivations for these measurements and the problematics driving the experiment design. Using large
throughput bolometers cooled at 0.3K we have a sensitivity high enough to detect CMB anisotropies at level ΔT/T∼10−5 in few seconds of integration time.
Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992. 相似文献
5.
Robert C. Nichol 《General Relativity and Gravitation》2008,40(2-3):249-267
In this review, I outline the use of galaxy correlations to constrain cosmological parameters. As with the cosmic microwave
background (CMB), the density of dark and baryonic matter imprints important scales on the fluctuations of matter and thus
the clustering of galaxies, e.g., the particle horizon at matter-radiation equality and the sound horizon at recombination.
Precision measurements of these scales from the baryon acoustic oscillations (BAO) and the large scale shape of the power
spectrum of galaxy clustering provide constraints on Ω
m
h
2. Recent measurements from the Sloan Digital Sky Survey (SDSS) and 2dF Galaxy Redshift Survey (2dFGRS) strongly suggest that
Ω
m
< 0.3. This forms the basic evidence for a flat Universe dominated by a Cosmological Constant (Λ) today (when combined with
results from the CMB and supernova surveys). Further evidence for this cosmological model is provided by the late-time Integrated
Sachs–Wolfe (ISW) effect, which has now been detected using a variety of tracers of the large scale structure in the Universe
out to redshifts of z > 1. The ISW effect also provides an opportunity to discriminate between Λ, dynamical dark energy models and the modification
of gravity on large scales. 相似文献
6.
Subir Sarkar 《General Relativity and Gravitation》2008,40(2-3):269-284
Several kinds of astronomical observations, interpreted in the framework of the standard Friedmann–Robertson–Walker cosmology,
have indicated that our universe is dominated by a Cosmological Constant. The dimming of distant Type Ia supernovae suggests
that the expansion rate is accelerating, as if driven by vacuum energy, and this has been indirectly substantiated through
studies of angular anisotropies in the cosmic microwave background (CMB) and of spatial correlations in the large-scale structure
(LSS) of galaxies. However there is no compelling direct evidence yet for (the dynamical effects of) dark energy. The precision CMB data can be equally well fitted without dark energy
if the spectrum of primordial density fluctuations is not quite scale-free and if the Hubble constant is lower globally than
its locally measured value. The LSS data can also be satisfactorily fitted if there is a small component of hot dark matter,
as would be provided by neutrinos of mass ∼0.5 eV. Although such an Einstein–de Sitter model cannot explain the SNe Ia Hubble
diagram or the position of the “baryon acoustic oscillation” peak in the autocorrelation function of galaxies, it may be possible
to do so, e.g. in an inhomogeneous Lemaitre–Tolman–Bondi cosmology where we are located in a void which is expanding faster
than the average. Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding
of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model,
rather than having physical reality. 相似文献
7.
The formation of inhomogeneities in CdxHg1-x
Te alloys upon post-growth cooling or upon low-temperature annealing is simulated numerically. The mechanism of the formation
of inhomogeneities is based on the diffusion instability in a system involving mercury atoms located at lattice sites, interstitial
mercury atoms, and cation vacancies. It is revealed that, upon prolonged annealing of the CdxHg1-x
Te alloys with a cadmium content x = 0.2 at a temperature of ∼200°C, the concentrations of mercury atoms at lattice sites, interstitial mercury atoms, and vacancies
are characterized by an inhomogeneous nearly periodical distribution arising from a small fluctuation when the initial equilibrium
concentration of interstitial mercury atoms exceeds a threshold value (∼3 × 1017 cm−3). The spatial and time scales of the concentration distribution are determined primarily by the equilibrium concentration
of vacancies and do not depend on the type of fluctuation involved. The spatial period of the concentration distribution increases
linearly from 0.01 to 3.00 μm as the equilibrium concentration of vacancies changes from 1019 to 1014 cm−3. At lower concentrations of vacancies, the periodic structure is formed for a considerably longer time. 相似文献
8.
Subodha Mishra 《International Journal of Theoretical Physics》2008,47(10):2655-2662
Considering our expanding universe as made up of gravitationally interacting particles which describe particles of luminous
matter, dark matter and dark energy which is represented by a repulsive harmonic potential among the points in the flat 3-space
and incorporating Mach’s principle into our theory, we derive a quantum mechanical relation connecting, temperature of the
cosmic microwave background radiation, age, and cosmological constant of the universe. When the cosmological constant is zero,
we get back Gamow’s relation with a much better coefficient. Otherwise, our theory predicts a value of the cosmological constant
2.0×10−56 cm−2 when the present values of cosmic microwave background temperature of 2.728 K and age of the universe 14 billion years are
taken as input. 相似文献
9.
Inflation with a scalar-field potential of the form λ (φ
2 − v
2)2 can be described in terms of a parametrical attractor with critical points, whose driftage depends on the control value of
the slowly changing Hubble rate. The method allows us to easily obtain theoretical expressions for fluctuations of inhomogeneity
in both the cosmic microwave background and distribution of matter. We find the region for admissible values of potential
parameters, wherein theoretical predictions are consistent with experimental results within the limits of measurement uncertainties. 相似文献
10.
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
11.
A large stack of lead-emulsion sandwich detector assembly was flown over Hyderabad, India. High energy gamma rays at the float
altitude were unambiguously identified from the cascades they induced, and their energies reliably determined by improved
methods. From an analysis of 163 gamma rays of energy ≳ 30 GeV, it is found that the differential energy spectrum is represented
by the power lawJ
r
(E)= 129·4E
−2·62±0·12 photons m−2 sr−1sec−1 GeV−1 at an effective atmospheric depth of 14·3 g cm−2; this is the first reliable balloon measurement of atmospheric gamma rays in the energy range 40–1000 GeV. After correcting
for the gamma rays radiated by the primary cosmic ray electrons, the production spectrum of gamma rays, resulting from the
collisions of cosmic ray nuclei with air nuclei, at the top of the atmosphere isP
r
(E, 0)=8·2 × 10−4 E2.60±0.09 photons g−1sr−1sec−1 GeV−1. The atmospheric propagation of the electromagnetic component due to the cascade process is also derived from the gamma ray
production spectrum. 相似文献
12.
In unparticle dark matter (unmatter) models, the equation of state of the unmatter is given by p=ρ/(2d
U+1), where d
U is the scaling factor. Unmatter with such equations of state would have a significant impact on the history of the expansion
of the universe. Using type Ia supernovae (SNIa), the baryon acoustic oscillation (BAO) measurements and the shift parameter
of the cosmic microwave background (CMB) to place constraints on such unmatter models, we find that if only the SNIa data
are used, the constraints are weak. However, with the BAO and CMB shift parameter data added, strong constraints can be obtained.
For the ΛUDM model, in which unmatter is the sole dark matter, we find that d
U>60 at 95% C.L. For comparison, in most unparticle physics models it is assumed that d
U<2. For the ΛCUDM model, in which unmatter co-exists with cold dark matter, we found that the unmatter can at most make up
a few percent of the total cosmic density if d
U<10; thus it cannot be the major component of dark matter. 相似文献
13.
S. E. Chigrinov K. K. Gudima A. I. Kievitskaya V. A. Petlitsky 《Hyperfine Interactions》1993,77(1):149-159
In this paper, we present a model of calculation with respect to the interactions of high-energy nuclei with matter. Based
on this model, we obtain results on energy and angular spectra of the n- and π−-particles produced in collisions of deuterium and tritium nuclei at energiesT
d=1 GeV/nucleon with light targets such as Li, Be. We have also estimated the production yields of neutrons and π−-mesons in targets of various radii, as well as mean energies of these these particles. Summarizing, we find that the lithium
target of radiusR=10−12 cm for which the energy cost επ to produce one π−-meson is estimated as 6.7 GeV/π for a d-beam and 5.3 GeV/π for a t-beam is the most preferred pion-production target. 相似文献
14.
We construct the supersymmetric economical 3-3-1 model which contains inflationary scenario and avoids the monopole puzzle.
Based on the spontaneous symmetry breaking pattern (with three steps), the F-term inflation is derived. The slow-roll parameters ∈ and η are calculated. By imposing as experimental five-year WMAP data on the spectral index n, we have derived a constraint on the number of e-folding N
Q
to be in the range from 25 to 50. The scenario for large-scale structure formation implied by the model is a mixed scenario
for inflation and cosmic string, and the contribution to the CMBR temperature anisotropy depends on the ratio M
X
/M
Pl. From the COBE data, we have obtained the constraint on the M
X
to be M
X
∈ [1.22 × 1016, 0.98 × 1017] GeV. The upper value M
X
≃ 1017 GeV is a result of the analysis in which the inflationary contribution to the temperature fluctuations measured by the COBE
is 90%. The coupling α varies in the range: 10−7−10−1. This value is not so small, and it is a common characteristics of the supersymmetric unified models with the inflationary
scenario. The spectral index n is a little bit smaller than 0.98. The SUGRA corrections are slightly different from the previous consideration. When ξ ≪ 1 and α lies in the above range, the spectral index gets the value consistent with the experimental five-year WMAP data. Comparing
with string theory, one gets ξ < 10−8. Numerical analysis shows that α ≈ 10−6. To get inflation contribution to the CMBR temperature anisotropy ≈90%, the mass scale M
X
< 3.5 × 1014 GeV. 相似文献
15.
17.
M. Aglietta B. Alessandro P. Antonioli F. Arneodo L. Bergamasco A. Campos Fauth C. Castagnoli A. Castellina C. Cattadori A. Chiavassa et al. 《Il Nuovo Cimento C》1992,15(4):441-446
Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower
array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement
the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y−1 (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E
0
)≈E
0
−2.5
, the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10−5erg cm−2. 相似文献
18.
For cold dark matter models, images of temperature fluctuations in the cosmic microwave background (CMB), due to Sunyaev Zel’dovich
(SZ) effect have been been simulated taking a cosmolgical distribution of clusters into account. All the models are normalised
to the 4-year COBE data. The image statistics are compared with the ATCA limits on arcmin scale anisotropy. The comparison
appears to favour low-Ω0 open universe models. 相似文献
19.
Yin-Zhe Ma Yan Gong Xuelei Chen 《The European Physical Journal C - Particles and Fields》2009,60(2):303-315
We investigate the observational signatures of the holographic dark-energy models, including both the original model and a
model with an interaction term between the dark energy and dark matter. We first delineate the dynamical behavior of such
models, especially considering whether they would have a “big rip” for different parameters; then we use several recent observations,
including 182 high-quality type Ia supernovae data observed with the Hubble Space Telescope, the SNLS and ESSENCE surveys,
42 latest Chandra X-ray cluster gas mass fraction, 27 high-redshift gamma-ray burst samples, the baryon acoustic oscillation
measurement from the Sloan Digital Sky Survey, and the CMB shift parameter from the WMAP three-year result to give more reliable
and tighter constraints on the holographic dark-energy models. The results of our constraints for the holographic dark-energy
model without interaction is c=0.748−0.009+0.108, Ω
m0=0.276−0.016+0.017, and for the model with interaction (c=0.692−0.107+0.135, Ω
m0=0.281−0.017+0.017, α=−0.006−0.024+0.021, where α is an interacting parameter). As these models have more parameters than the ΛCDM model, we use the Bayesian Evidence as a model-selection criterion to make comparisons. We found that the holographic
dark-energy models are mildly favored by the observations as compared to the ΛCDM model. 相似文献
20.
A. N. Vystavkin D. V. Shuvaev L. S. Kuz’min M. A. Tarasov E. Aderstedt M. Willander T. Claeson 《Journal of Experimental and Theoretical Physics》1999,88(3):598-602
This paper describes the design and experimental testing of a high-sensitivity hot-electron bolometer based a film of normal
metal, exploiting the Andreev reflection from superconductor boundaries, and cooled with the help of a superconductor-insulator-normal
metal junction. At the measured thermal conductivity, G≈6×10−12 W/K, and a time constant of τ=0.2 μs, and a temperature of 300 mK, the estimated noise-equivalent power NEP=5×10−18 W/Hz1/2, assuming that temperature fluctuations are the major source of noise. At a temperature of 100 mK, the thermal conductivity
drops to G≈7×10−14 W/K, which yields NEP=2×10−19 W/Hz1/2 at a time constant of τ=5 μs. The microbolometer has been designed to serve as a detector of millimeter and FIR waves in space-based radio telescopes.
Zh. éksp. Teor. Fiz. 115, 1085–1092 (March 1999) 相似文献