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1.
《Comptes Rendus Physique》2003,4(8):891-899
One of the main challenges facing upcoming Cosmic Microwave Background (CMB) experiments aiming at measuring temperature anisotropies with great accuracy will be to assess the contamination of CMB measurements by galactic and extragalactic foregrounds. On the extragalactic side, confusion noise from extragalactic sources hampers the detection of intrinsic CMB anisotropies at small angular scales. Secondary CMB anisotropies must also be carefully accounted for in order to isolate the primordial fluctuations. We present in this article a brief overview of the extragalactic contributions to the CMB. The galactic foregrounds are discussed elsewhere (Giard and Lagache, this issue). To cite this article: G. Lagache, N. Aghanim, C. R. Physique 4 (2003). 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.
David L. Clements 《Contemporary Physics》2017,58(4):331-348
4.
Summary We consider a ?two phase? accretion disk consisting of an optically thick layer with temperatureT≃104 K embedded in a hot thin corona (T≃109 K). The main energy input occurs through magnetic heating of the electrons in the corona, while cooling is due to Compton
losses of the hot electrons on the soft photons provided by the thick layer. We write the balance equations for the two phases.
We show that a possible mode of variability yields steeper spectra for increasing soft-photon luminosity as observed in Seyfert
galaxies and compute composite model spectra in the X-ray range, via Monte Carlo simulations.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献
5.
P. Merluzzi A. Rotundi L. Colangeli V. Mennella P. Andreani G. Dall'Oglio L. Pizzo E. Bussoletti 《Il Nuovo Cimento C》1993,16(5):643-649
Summary We have considered some millimetric observations of our Galaxy and of the Large Magellanic Cloud (LMC) taken at the Italian
Base in Antarctica. Using other submm data and fitting all the observations with a modified Planck curve, we have obtained
useful information about the temperaureT and the spectral index α of the dust grains both for the Galaxy and the LMC. For the galactic spectrum two different couples
ofT and α match the detected fluxes:a)T=7K, α=2;b)T=15K, α=1.1. We have tried to identify the nature of the dust grains responsible for the submm and mm emission by comparing
these results with the spectral trend of some cosmic analogues studied in laboratory.
Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992. 相似文献
6.
Varun Sahni 《Pramana》2000,55(1-2):43-52
I present a short overview of current observational results and theoretical models for a cosmological constant. The main motivation
for invoking a small cosmological constant (or A-term) at the present epoch has to do with observations of high redshift Type
Ia supernovae which suggest an accelerating universe. A flat accelerating universe is strongly favoured by combining supernovae
observations with observations of CMB anisotropies on degree scales which give the ‘best-fit’ values ΘA ⋍ 0.7 and Θ
m
⋍ 0.3. A time dependent cosmological A-term can be generated by scalar field models with exponential and power law potentials.
Some of these models can alleviate the ‘fine tuning’ problem which faces the cosmological constant. 相似文献
7.
Xian Gao 《Physics letters. [Part B]》2011,702(4):197-200
We show that modified gravity presents distinctive nonlinear features on the Cosmic Microwave Background (CMB) anisotropies comparing with General Relativity (GR). We calculate the contribution to the CMB non-Gaussianity from nonlinear Sachs-Wolfe effect in f(R) gravity and show that, contrary to GR?s contribution which is typically ?O(1), the contribution in f(R) gravity is sensitive to the nonlinear structure of f(R) and can be large in principle. Optimistically, this gives an alternative origin for the possibly observed large CMB non-Gaussianities besides the primordial ones. On the other hand, such nonlinear features can be employed to provide a new cosmological test of f(R) or other modified theories of gravitation, which is unique and independent of previously known tests. 相似文献
8.
We have carried out an extensive study of electronic properties of silver iodide in β- and γ-phases. The theoretical Compton profiles, energy bands, density of states and anisotropies in momentum densities are computed
using density functional theories. We have also employed full-potential linearized augmented plane-wave method to derive the
energy bands and the density of states. To compare our theoretical data, isotropic Compton profile measurement on γ-AgI using 137Cs Compton spectrometer at an intermediate resolution of 0.38 a.u. has been undertaken. The theoretical anisotropies are also
interpreted on the basis of energy bands. 相似文献
9.
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
10.
Summary We report on the experimental results obtained with the cryogenic Gravitational-Wave resonant detector ALTAIR located in Frascati
(Italy) at the Istituto di Fisica dello Spazio Interplanetario of Consiglio Nazionale delle Ricerche. The peculiarity of this
experiment is its working frequency. The first longitudinal mode of resonance of the antenna is at 1.8 kHz. The antenna, now
equipped with a resonant capacitive transducer and a d.c. SQUID preamplifier, after a first test in November 1989, has operated
almost continuously from May 1990. The best sensitivity, recently reached, expressed in terms of the effective noise temperatureT
eff, is 20 mK, corresponding, for a short pulse of gravitational wave, to a metric perturbationh of 3×10−18. In the last period of measurements (from April 1991 to March 1992) two other antennas were operating: the Explorer antenna
(2300 kg,T=2.0 K) at CERN in Geneva and the LSU antenna (2500 kg,T=4.2 K) at Louisiana State University in USA, both having a resonant frequency below 1 kHz. The data of these three detectors
can be remote observed, in real time, by the international computer network. Coincidence analysis between the data of these
three detectors is in progress.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990 (updated version). 相似文献
11.
S. Abd El-Samad R. Bilger K. -Th. Brinkmann H. Clement M. Dietrich E. Doroshkevich S. Dshemuchadse A. Erhardt W. Eyrich A. Filippi H. Freiesleben M. Fritsch R. Geyer A. Gillitzer J. Hauffe D. Hesselbarth R. Jaekel B. Jakob L. Karsch K. Kilian H. Koch J. Kress E. Kuhlmann S. Marcello S. Marwinski R. Meier K. Möller H. P. Morsch L. Naumann E. Roderburg P. Schönmeier M. Schulte-Wissermann W. Schroeder M. Steinke F. Stinzing G. Y. Sun J. Wächter G. J. Wagner M. Wagner U. Weidlich A. Wilms S. Wirth G. Zhang P. Zupranski 《The European Physical Journal A - Hadrons and Nuclei》2006,30(2):443-453
The single-pion production reactions pp → dπ+, pp → npπ+ and pp → ppπ0 were measured at a beam momentum of 0.95GeV/c ( T
p ≈ 400MeV) using the short version of the COSY-TOF spectrometer. The implementation of a central calorimeter provided particle
identification, energy determination and neutron detection in addition to time-of-flight and angle measurements. Thus, all
pion production channels were recorded with 1-4 overconstraints. The total and differential cross-sections obtained are compared
to previous data and theoretical calculations. Main emphasis is put on the discussion of the ppπ0 channel, where we obtain angular distributions different from previous experimental results, however, partly in good agreement
with recent phenomenological and theoretical predictions. In particular, we observe very large anisotropies for the π0 angular distributions in the kinematical region of small relative proton momenta revealing there a dominance of proton spinflip
transitions associated with π0
s and d partial waves and emphasizing the important role of π0
d-waves. 相似文献
12.
We consider ferromagnetic Ising systems where the interaction is given by the sum of a fixed reference potential and a Kac
potential of intensity λ≥0 and scaling parameter γ>0$. In the Lebowitz Penrose limit γ→0+$ the phase diagram in the (T,λ) positive quadrant is described by a critical curve λmf(T), which separates the regions with one and two phases, respectively below and above the curve. We prove that if $λ>mf(T), i.e. above the curve, there are at least two Gibbs states for small values of γ. If instead λ<λmf(T) and if the reference Gibbs state (i.e. without the Kac potential) satisfies a mixing condition at the temperature T, then, at the same temperature the full interaction (i.e. with also the Kac potential) satisfies the Dobrushin Shlosman
uniqueness condition for small values of γ so that there is a unique Gibbs state.
Received: 9 April 1996 / Accepted: 26 November 1996 相似文献
13.
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
14.
Ya. V. Fominov A. A. Golubov T. Yu. Karminskaya M. Yu. Kupriyanov R. G. Deminov L. R. Tagirov 《JETP Letters》2010,91(6):308-313
We study the critical temperature T
c
of SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting
component is generated at noncollinear magnetizations of the F layers. We demonstrate that T
c
can be a nonmonotonic function of the angle α between the magnetizations of the two F layers. The minimum is achieved at
an intermediate α, lying between the parallel (P, α = 0) and antiparallel (AP, α = π) cases. This implies a possibility of
a “triplet” spin-valve effect: at temperatures above the minimum T
c
Tr but below T
c
P and T
c
AP, the system is superconducting only in the vicinity of the collinear orientations. At certain parameters, we predict a reentrant
T
c
(α) behavior. At the same time, considering only the P and AP orientations, we find that both the “standard” (T
c
P < T
c
AP) and “inverse” (T
c
P > T
c
AP) switching effects are possible depending on parameters of the system. 相似文献
15.
We investigate the effects of a weak gravitational wave, modelled as a gaussian wavepacket, on the polarization state of an
electromagnetic field enclosed in a cavity. Our approach is semiclassical, in that the electromagnetic field is described as a quantum field, while the gravitational perturbation is treated classically,
as a slightly curved background spacetime. Assuming that before the interaction the electromagnetic field has been prepared
in a given polarization state, we show that – due to the gravitational scattering with the wave – some photons having different
polarization states are found in the cavity at late times. Such polarization scattering has some resemblance with Thomson
scattering, well-known in Quantum Electrodynamics: hence the motivation for the title. We give a numerical estimate of the
resulting photon polarization spreading in the case of a typical gravitational burst from a final supernova rebound. We also
briefly comment about the possible influence of such gravitational scattering on the Cosmic Microwave Background (CMB) polarization. 相似文献
16.
Varun Sahni 《Pramana》2000,55(4):559-573
This talk presents a brief overview of recent results pertaining to the cosmological constant ‘A’. I summarize the observational
situation focussing on observations of high redshift Type Ia supernovae which suggest A > 0. Observations of small angular
anisotropies in the cosmic microwave background complement Type Ia supernovae observations and both CMB and Sn can be combined
to place strong constraints on the value of A. The presence of a small A-term increases the age of the universe and slows
down the formation of large scale structure. I also review recent theoretical attempts to generate a small A-term at the current
epoch and a model independent approach for determining the cosmic equation of state. 相似文献
17.
Krzysztof Bolejko 《General Relativity and Gravitation》2009,41(8):1737-1755
This paper presents the application of the Szekeres Swiss Cheese model to the analysis of observations of the cosmic microwave
background (CMB) radiation. The impact of inhomogeneous matter distribution on the CMB observations is in most cases studied
within the linear perturbations of the Friedmann model. However, since the density contrast and the Weyl curvature within
the cosmic structures are large, this issue is worth studying using another approach. The Szekeres model is an inhomogeneous,
non-symmetrical and exact solution of the Einstein equations. In this model, light propagation and matter evolution can be
exactly calculated, without such approximations as small amplitude of the density contrast. This allows to examine in more
realistic manner the contribution of the light propagation effect to the measured CMB temperature fluctuations. The results
of such analysis show that small-scale, non-linear inhomogeneities induce, via Rees-Sciama effect, temperature fluctuations
of amplitude 10−7–10−5 on angular scale ϑ < 0.24° (ℓ > 750). This is still much smaller than the measured temperature fluctuations on this angular scale. However, local and uncompensated
inhomogeneities can induce temperature fluctuations of amplitude as large as 10−3, and thus can be responsible the low multipoles anomalies observed in the angular CMB power spectrum. 相似文献
18.
《Comptes Rendus Physique》2015,16(10):891-913
The Planck mission prime objective was a very accurate and complete measurement of the temperature anisotropies of the Cosmic Microwave Background (CMB). Cosmological results from the intensity data of the nominal mission of a duration of 15 months were disclosed on 21 March 2013. Fortunately, the satellite kept acquiring data for at least twice longer, and we announced in February 2015 new results based on all the data acquired, both in temperature and polarization. I provide a short overview of the latest data and findings of most interest for inflation, as a basis for the other contributions to this volume. This overview is entirely based on the published or submitted works of the Planck collaboration. 相似文献
19.
《Comptes Rendus Physique》2003,4(8):819-821
We introduce the main issues related to the new cosmological advances coming from observations of the Cosmic Microwave Background (CMB). These issues are then detailed in the following articles of this special CMB volume. To cite this article: F.-X. Désert, C. R. Physique 4 (2003). 相似文献
20.
A W Wolfendale 《Pramana》1979,12(6):631-651
Cosmic rays were discovered in 1911 but it is only now that some ideas are beginning to emerge as to their origin. This paper
will examine the present evidence concerning the origin question over the whole energy range, from 109 eV to 1020 eV.
At the lowest energies, (109–1010 eV), the new subject of gamma ray astronomy plays a crucial role and a galactic origin is favoured. At higher energies (1012–1017 eV) recent measurements of the anisotropies in arrival directions also suggest a galactic origin, although the evidence is
not as strong.
At the very highest energies it seems likely that some, at least, of the particles come from outside the galaxy although the
non-existence of the cut-off at about 6 × 1019 eV arising from interactions with the cosmological relict radiation provides a paradox. The likely future areas of advance
in this fascinating subject will be indicated.
Based on the B. B. Roy memorial lectures delivered at Calcutta University, February 1–3, 1978. 相似文献