共查询到20条相似文献,搜索用时 15 毫秒
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Mairi Sakellariadou 《International Journal of Theoretical Physics》1997,36(11):2503-2511
Acoustic peaks in the angular power spectrum of the cosmic microwave background anisotropies may allow us to distinguish among
the two classes of models—topological defect scenarios and inflationary models—which attempt to explain the origin of structure
formation in the universe. I briefly sketch the main differences between these two classes of models and illustrate the relevant
analysis of induced density perturbations, in a model where density perturbations are generated by global scalar fields, within
a universe dominated by cold dark matter. 相似文献
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Das S Sherwin BD Aguirre P Appel JW Bond JR Carvalho CS Devlin MJ Dunkley J Dünner R Essinger-Hileman T Fowler JW Hajian A Halpern M Hasselfield M Hincks AD Hlozek R Huffenberger KM Hughes JP Irwin KD Klein J Kosowsky A Lupton RH Marriage TA Marsden D Menanteau F Moodley K Niemack MD Nolta MR Page LA Parker L Reese ED Schmitt BL Sehgal N Sievers J Spergel DN Staggs ST Swetz DS Switzer ER Thornton R Visnjic K Wollack E 《Physical review letters》2011,107(2):021301
We report the first detection of the gravitational lensing of the cosmic microwave background through a measurement of the four-point correlation function in the temperature maps made by the Atacama Cosmology Telescope. We verify our detection by calculating the levels of potential contaminants and performing a number of null tests. The resulting convergence power spectrum at 2° angular scales measures the amplitude of matter density fluctuations on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The measured amplitude of the signal agrees with Lambda cold dark matter cosmology predictions. Since the amplitude of the convergence power spectrum scales as the square of the amplitude of the density fluctuations, the 4σ detection of the lensing signal measures the amplitude of density fluctuations to 12%. 相似文献
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We derive the primordial power spectrum of density fluctuations in the framework of quantum cosmology. For this purpose we perform a Born-Oppenheimer approximation to the Wheeler-DeWitt equation for an inflationary universe with a scalar field. In this way, we first recover the scale-invariant power spectrum that is found as an approximation in the simplest inflationary models. We then obtain quantum gravitational corrections to this spectrum and discuss whether they lead to measurable signatures in the cosmic microwave background anisotropy spectrum. The nonobservation so far of such corrections translates into an upper bound on the energy scale of inflation. 相似文献
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《Physics letters. [Part B]》1987,199(3):346-350
We analyse distortions of the spectrum of microwave background radiation caused by heating of cosmic plasma by the population of superconducting cosmic string loops. We find that the effect in the Rayleigh-Jeans part of the spectrum is at the observational level and may be used to constrain the parameters of the cosmological model by Ostriker, Thompson and Witten. 相似文献
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《Physics Reports》2002,365(4):251-333
Nature abhors an infinity. The limits of general relativity are often signaled by infinities: infinite curvature as in the center of a black hole, the infinite energy of the singular big bang. We might be inclined to add an infinite universe to the list of intolerable infinities. Many theories that move beyond general relativity naturally treat space as finite. In this review we discuss the mathematics of finite spaces and our aspirations to observe the finite extent of the universe in the cosmic background radiation. 相似文献
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T R Seshadri 《Pramana》1999,53(6):963-969
In re-ionized models, the measurement of polarization of CMBR can be a good criterion to narrow down the parameter space for
cosmological models. A Vishniac-type effect in second order polarization over arc minute scales has been calculated. It has
been shown that while the effect is very small (∼10−2
μK) for CDM models, it can be significant (∼0.3μK) for some isocurvature models. 相似文献
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Possible Lorentz-violating effects in the cosmic microwave background are studied. We provide a systematic classification of renormalizable and nonrenormalizable operators for Lorentz violation in electrodynamics and use polarimetric observations to search for the associated violations. 相似文献
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The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic feature of ultra-large scale structure
of the cosmos, in particular, of non-trivial cosmic topology. The statistical isotropy (SI) of the cosmic microwave background
temperature fluctuations (CMB anisotropy) is sensitive to this breakdown on the largest scales comparable to, and even beyond
the cosmic horizon. We propose a set of measures,K
l
(l = 1, 2,3,...) which for non-zero values indicate and quantify statistical isotropy violations in a CMB map. We numerically
compute the predictedK
l
spectra for CMB anisotropy in flat torus universe models. Characteristic signatures of different models in theK
l
spectrum are noted. 相似文献
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To minimize instrumentally the induced systematic errors, cosmic microwave background (CMB) anisotropy experiments measure
temperature differences across the sky using pairs of horn antennas, temperature map is recovered from temperature difference
obtained in sky survey through a map-making procedure. To inspect and calibrate residual systematic errors in the recovered
temperature maps is important as most previous studies of cosmology are based on these maps. By analyzing pixel-ring coupling
and latitude dependence of CMB temperatures, we find notable systematic deviation from CMB Gaussianity in released Wilkinson
Microwave Anisotropy Probe (WMAP) maps. The detected deviation cannot be explained by the best-fit LCDM cosmological model
at a confidence level above 99% and cannot be ignored for a precision cosmology study.
Supported by the National Natural Science Foundation of China (Grant No. 10533020), the National Basic Research Program of
China (Grant No. 2009CB-824800), and the Directional Research Project of the Chinese Academy of Sciences (Grant No. KJCX2-YW-T03)
Contributed by LI TiPei 相似文献
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Tarun Souradeep 《Pramana》2006,67(4):699-710
Measurements of CMB anisotropy and, more recently, polarization have played a very important role in allowing precise determination
of various parameters of the ‘standard’ cosmological model. The expectation of the paradigm of inflation and the generic prediction
of the simplest realization of inflationary scenario in the early Universe have also been established — ‘acausally’ correlated
initial perturbations in a flat, statistically isotropic Universe, adiabatic nature of primordial density perturbations. Direct
evidence for gravitational instability mechanism for structure formation from primordial perturbations has been established.
In the next decade, future experiments promise to strengthen these deductions and uncover the remaining crucial signature
of inflation — the primordial gravitational wave background. 相似文献
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Ruth Durrer 《International Journal of Theoretical Physics》1997,36(11):2469-2487
The analysis of anisotropies in the cosmic microwave background (CMB) has become an extremely valuable tool for cosmology.
There is even hope that planned CMB anisotropy experiments may revolutionize cosmology. Together with determinations of the
CMB spectrum, they represent the first precise cosmological measurements. The value of CMB anisotropies lies in large part
in the simplicity of the theoretical analysis. Fluctuations in the CMB can be determined almost fully within linear cosmological
perturbation theory and are not severely influenced by complicated nonlinear physics. In this contribution the different physical
processes causing or influencing anisotropies in the CMB are discussed: the geometry perturbations at and after last scattering,
the acoustic oscillations in the baryon-photon plasma prior to recombination, and the diffusion damping during the process
of recombination. The perturbations due to the fluctuating gravitational field, the so-called Sachs-Wolfe contribution, is
described in a very general form using the Weyl tensor of the perturbed geometry. 相似文献