共查询到20条相似文献,搜索用时 0 毫秒
1.
Brillouin scattering of photons off the density fluctuations in a fluid is potentially important for cosmology. We derive the Brillouin spectral distortion of blackbody radiation, and discuss the possible implications for the cosmic microwave background. The thermal Sunyaev-Zeldovich effect is slightly modified by Brillouin distortion, but only at very long wavelengths. 相似文献
2.
Xian Gao 《Physics letters. [Part B]》2011,702(1):12-15
We investigate the effects of the presence of relic classical superhorizon inhomogeneities during inflation. This superhorizon inhomogeneity appears as a gradient locally and picks out a preferred direction. Quantum fluctuations on this slightly inhomogeneous background are generally statistical anisotropic. We find a quadrupole modification to the ordinary isotropic spectrum. Moreover, this deviation from statistical isotropy is scale-dependent, with a ∼−1/k2 factor. This result implies that the statistical anisotropy mainly appears on large scales, while the spectrum on small scales remains highly isotropic. Moreover, due to this −1/k2 factor, the power on large scales is suppressed. Thus, our model can simultaneously explain the observed anisotropic alignments of the low-? multipoles and their low power. 相似文献
3.
Recent released WMAP data show a low value of quadrupole in the CMB temperature fluctuations, which confirms the early observations by COBE. In this Letter we consider a model of two inflatons with different masses,
, m1>m2 and study its effects on CMB of suppressing the primordial power spectrum P(k) at small k. Inflation is driven in this model firstly by the heavier inflaton φ1, then the lighter field φ2. But there is no interruption in between. We numerically calculate the scalar and tensor power spectra with mode by mode integrations, then fit the model to WMAP temperature correlations TT and the TE temperature-polarization spectra. Our results show that with m11014 GeV and m21013 GeV, this model solves the problems of flatness, etc. and the CMB quadrupole predicted can be much lower than the standard power-law ΛCDM model. 相似文献
4.
A digitalized temperature map is recovered from the first light sky survey image published by the Planck team, from which an angular power spectrum of the cosmic microwave background (CMB) is derived. The amplitudes of the low multipoles (low-l) measured from the preliminary Planck power spectrum are significantly lower than those reported by the WMAP team. Possible systematical effects are far from enough to explain the observed low-l differences. 相似文献
5.
Ashoke Sen 《Pramana》2004,62(2):403-413
We summarize the recent developments in the study of time dependent solutions describing the rolling of a tachyon on a non-BPS
D-brane system. 相似文献
6.
Via compactification on a circle, the matrix mode] of M-theory proposed by Banks et a]. suggests a concrete identification between the large N limit of two-dimensional N = 8 supersymmetric Yang-Mills theory and type IIA string theory. In this paper we collect evidence that supports this identification. We explicitly identify the perturbative string states and their interactions, and describe the appearance of D-particle and D-membrane states. 相似文献
7.
Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular, we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude Bλ and the power spectral index nB and discuss prospects for better determining these quantities in the near future. 相似文献
8.
Loop variables and gauge invariant exact renormalization group equations for (open) string theory II
In arXiv:1202.4298 gauge invariant interacting equations were written down for the spin 2 and spin 3 massive modes using the exact renormalization group of a world sheet theory. This is generalized to all the higher levels in this paper. An interacting theory of an infinite tower of massive higher spins is obtained. They appear as a compactification of a massless theory in one higher dimension. The compactification and consequent mass is essential for writing the interaction terms. Just as for spin 2 and spin 3, the interactions are in terms of gauge invariant “field strengths” and the gauge transformations are the same as for the free theory. This theory can then be truncated in a gauge invariant way by removing one oscillator of the extra dimension to match the field content of BRST string (field) theory. The truncation has to be done level by level and results are given explicitly for level 4. At least up to level 5, the truncation can be done in a way that preserves the higher-dimensional structure. There is a relatively straightforward generalization of this construction to (arbitrary) curved space–time and this is also outlined. 相似文献
9.
We construct a four-generation MSSM with rank-4 Yukawa matrices from intersecting D6 branes on a T6/(Z2×Z2) orientifold. The Yukawa matrices obtained provide an example of Flavor Democracy (FD), where the Yukawa couplings are all nearly equal. Mass hierarchies may then be generated by slight perturbations away from FD. We find that it is possible to obtain hierarchical masses for the quarks and leptons of each generation and mixings between them. In addition, the tree-level gauge couplings are unified at the string scale. Finally, we also construct similar models with one, two, and three generations in which the rank of the Yukawa matrices is equal to the number of generations in each model. 相似文献
10.
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
11.
Sunil Mukhi 《Pramana》2002,58(1):21-26
A boundary-state computation is performed to obtain derivative corrections to the Chern-Simons coupling between a p-brane and the RR gauge potential C
p
−3. We work to quadratic order in the gauge field strength F, but all orders in derivatives. In a certain limit, which requires the presence of a constant B-field background, it is found that these corrections neatly sum up into the *2 product of (commutative) gauge fields. The result is in agreement with a recent prediction using noncommutativity. 相似文献
12.
Kerrr in the title is not a typo. The third “r” stands for regular, in the sense of pathology-free rotating black hole. We exhibit a long search-for, exact, Kerr-like, solution of the Einstein equations with novel features: (i) no curvature ring singularity; (ii) no “anti-gravity” universe with causality violating time-like closed world-lines; (iii) no “super-luminal” matter disk. 相似文献
13.
《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
14.
In this paper we analyze theoretically and experimentally the effect of tilt of the roof mirrors in a double pendulum Martin-Puplett Polarizing Interferometer (MPI), focusing on the polarization of the interfering beams. In principle, the tilt affects the efficiency and polarimetric properties of the interferometer. The case of a moderate resolution spectrometer is analysed in detail. Using the Stokes formalism we recover the analytical expressions for the orientation angle and the ellipticity of the beam reflected from a metallic surface, and we compute these quantities for the roof-mirror of a MPI. We find that the polarization rotation and depolarization are small. Using the Jones formalism we propagate their effect on the measured interferogram and spectrum, and demonstrate that the performance degradation is small compared to other systematic effects. 相似文献
15.
The purpose of our study is to understand the mathematical origin in real space of modulated and damped sinusoidal peaks observed in cosmic microwave background radiation anisotropies. We use the theory of the Fourier transform to connect localized features of the two-point correlation function in real space to oscillations in the power spectrum. We also illustrate analytically and by means of Monte Carlo simulations the angular correlation function for distributions of filled disks with fixed or variable radii capable of generating oscillations in the power spectrum. While the power spectrum shows repeated information in the form of multiple peaks and oscillations, the angular correlation function offers a more compact presentation that condenses all the information of the multiple peaks into a localized real space feature. We have seen that oscillations in the power spectrum arise when there is a discontinuity in a given derivative of the angular correlation function at a given angular distance. These kinds of discontinuities do not need to be abrupt in an infinitesimal range of angular distances but may also be smooth, and can be generated by simply distributing excesses of antenna temperature in filled disks of fixed or variable radii on the sky, provided that there is a non-null minimum radius and/or the maximum radius is constrained. 相似文献
16.
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
17.
Sandip P. Trivedi 《Pramana》2004,63(4):777-783
We discuss a recent proposal to construct de Sitter vacua in string theory. It is based on flux compactifications in string
theory where all the moduli are stabilised and supersymmetry is broken with control. The resulting picture is that of a complicated
landscape with many vacua of widely varying values for the cosmological constant. 相似文献
18.
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
19.
G. Lessner 《General Relativity and Gravitation》2004,36(5):903-922
It is shown that the widely accepted interpretation of the peaks in the CMB as acoustic oscillations seems to be not correct. It is further shown that the peaks correspond to the extension of galaxies in a non-standard scenario of galaxy formation forwarded by the author in a previous paper. Hence this result and the generating mechanism of the peaks by amplification of zero-point quantum oscillations in the very early universe as proposed by Bose and Grishchuk might complement one another to an overall picture of galaxy formation. 相似文献
20.