共查询到20条相似文献,搜索用时 0 毫秒
1.
Subhendra Mohanty 《Pramana》2000,54(1):93-100
I discuss basic theory of effect of the properties of the cosmological relict neutrinos on the observations of the cosmic
microwave background anisotropy. 相似文献
2.
Robert G. Crittenden 《Pramana》2004,63(4):829-836
It has been a little over a year since WMAP produced its dramatic new glimpse of the cosmic microwave background. I review
the results of the WMAP mission and the science that has arisen from it, focusing on the qualitatively new features of the
data: the temperature-polarization correlation, correlations with large scale structure, the large-scale power deficit and
its implications, and the search for non-Gaussianity. 相似文献
3.
Subhabrata Majumdar 《Pramana》2004,63(4):871-875
Surveys of clusters of galaxies provide us with a powerful probe of the density and nature of the dark energy. The red-shift
distribution of detected clusters is highly sensitive to the dark energy equation of state parameterw. Upcoming Sunyaev-Zel’dovich (SZ) surveys would provide us large yields of clusters to very high red-shifts. Self-calibration
of cluster scaling relations, possible for such a huge sample, would be able to constrain systematic biases on mass estimators.
Combining cluster red-shift abundance with limited mass follow-up and cluster mass power spectrum can then give constraints
onw, as well as onσ
8 and ΩM to a few per cents. 相似文献
4.
《Comptes Rendus Physique》2015,16(10):948-959
The cosmic microwave background is the most precise and the most simple cosmological dataset. This makes it our most prominent window to the physics of the very early Universe. In this article I give an introduction to the physics of the cosmic microwave background and show in some detail how primordial fluctuations from inflation are imprinted in the temperature anisotropy and polarisation spectrum of the CMB. I discuss the main signatures that are suggesting an inflationary phase for the generation of initial fluctuations. 相似文献
5.
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
6.
简单介绍了近年来关于宇宙微波背景辐射在观测上取得的重大进展,以及有关它的解释、理论和意义.宇宙微波背景是我们了解宇宙奥秘的一个至关重要的窗口.在未来几年,它还将扮演更加重要的角色. 相似文献
7.
简单介绍了近年来关于宇宙微波背景辐射在观测上取得的重大进展,以及有关它的解释、理论和意义.宇宙微波背景是我们了解宇宙奥秘的一个至关重要的窗口.在未来几年,它还将扮演更加重要的角色. 相似文献
8.
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
9.
Ralf Hofmann 《Annalen der Physik》2015,527(3-4):254-264
Presuming that CMB photons are described by the deconfining phase of an SU(2) Yang‐Mills theory with the critical temperature for the deconfining‐preconfining phase transition matching the present CMB temperature K (SU(2)CMB), we investigate how CMB temperature T connects with the cosmological scale factor a in a Friedmann‐Lemaître‐Robertson‐Walker Universe. Owing to a violation of conformal scaling at late times, the tension between the (instantaneous) redshift of reionisation from CMB observation () and quasar spectra () is repealed. Also, we find that the redshift of CMB decoupling moves from to which questions ΛCDM cosmology at high redshifts. Adapting this model to the conventional physics of three flavours of massless cosmic neutrinos, we demonstrate inconsistency with the value Neff ~ 3.36 extracted from Planck data. Interactions between cosmic neutrinos and the CMB implies a common temperature T of (no longer separately conserved) CMB and neutrino fluids. Neff ~ 3.36 then entails a universal, temperature induced cosmic neutrino mass with . Our above results on zre and zdec, derived from SU(2)CMB alone, are essentially unaffected when including such a neutrino sector.
10.
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
11.
文章基于大爆炸宇宙学描述了发生于宇宙早期的中微子退耦与轻核素合成事件。退耦后的中微子形成宇宙的背景之一。文章介绍了几种探测宇宙背景中微子的方法,侧重于利用b衰变核俘获超低动能的中微子。 相似文献
12.
文章基于大爆炸宇宙学描述了发生于宇宙早期的中微子退耦与轻核素合成事件。退耦后的中微子形成宇宙的背景之一。文章介绍了几种探测宇宙背景中微子的方法,侧重于利用β衰变核俘获超低动能的中微子。 相似文献
13.
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
14.
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
15.
16.
U. A. Yajnik 《Pramana》2004,63(6):1317-1330
We present an overview of the implications of the WMAP data for particle physics. The standard parameter set ∈, η and ξ characterising
the inflaton potential can be related to the power-law indices characterising deviation of the CMB spectrum from the scale
invariant form. Different classes of inflation potentials are in turn naturally associated with different unified schemes.
At present WMAP does not exclude any but a few simple unified models. In particular, hybrid models favoured by supersymmetric
unification continue to be viable. However future improvement in data leading to better determination of the ‘running’ of
power-law indices should help to narrow the possibilities for unified models. The main conclusion is that WMAP is consistent
with the paradigm of GUT scale (1016 GeV) inflation. 相似文献
17.
O. S. Sazhina M. V. Sazhin V. N. Sementsov 《Journal of Experimental and Theoretical Physics》2008,106(5):878-887
A method of searching for cosmic strings based on an analysis of the cosmic microwave background (CMB) anisotropy is presented. A moving straight cosmic string is shown to generate structures of enhanced and reduced brightness with a distinctive shape. The conditions under which a string can be detected by both CMB anisotropy and gravitational lensing in optical surveys are analyzed. For a relativistic string with a deficit angle of ~1″–2″, the amplitude of the generated anisotropy is shown to be ~15–30 μK. 相似文献
18.
19.
David L. Clements 《Contemporary Physics》2017,58(4):331-348
20.
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