宇宙微波背景辐射的观测和理论

介绍了有关宇宙微波背景辐射（ＣＢＲ）观测和理论研究的最新进展。叙述了基于ＣＯＢＥ卫星的观测宇宙学,包括对背景辐射谱,各向异性的观测结果及其理论意义;并系统介绍了ＣＢＲ各向异性形成的种种机制;展望了下一代宇宙微波背景探测器（ＭＡＰ和ＰＬＡＮＣＫ）的科学目标和主要技术参数。     

Polarization of Cosmic Microwave Backgdound Scattered by Moving Flat Protoobjects

The work is devoted to the investigations of possible observational manifestations of protoobjects related to the dark ages epoch (10 < z < 1000), before formation of self-luminous galaxies and stars. These objects can distort the cosmic microwave background. Formation of these objects is described in the pancake theory and in the model of hierarchic clustering. According to these theories we may consider these protoobjects as flat layers. We consider both Thomson (with Rayleigh phase matrix) and resonance (for complete frequency redistribution) scattering of cosmic microwave background radiation by a moving flat layer. The resulting anisotropy and polarization of cosmic microwave radiation are calculated for a wide range of layer optical thickness (from an optically thin layer to an optically thick one). Analytical solutions are also obtained for the case of an optically thin layer and are compared with the numerical ones.     

宇宙微波背景辐射极化的近似解析公式

在宇宙早期的退耦过程中，光子与电子发生Thompson散射．光子气体空间分布的各向异性通过Thompson散射而产生宇宙微波背景辐射的极化，并为最近WMAP观测到．从光子气体的Boltzmann方程出发，采用一般的光深函数，分别积分给出原初密度扰动和残余引力波产生的微波背景辐射极化的近似解析解，结果适用于一般的复合过程．密度扰动FS所产生极化的近似解析解为βS≌-CFs(Td)ΔTd，其中Td和△Td分别为退耦时刻和退耦宽度，系数C≌(0．08—0．12)，明显依赖于复合模型．残余引力波扰动FT产生极化的积分稍微复杂，在长波近似下我们对原初扰动按波数进行幂级数展开，保留到两项FT≌FT^(1) FT(2)，分别积分，给出近似解析解βT≌-[CFT^(1)(Td) DFT^(2)(Td)]ΔTd.第一项的极化与密度扰动类似，结论也相同；但第二项的系数D≌(0．22—0．32)，远大于系数C，我们的近似解析解有助于理解背景辐射的温度一极化交叉关联和检测残余引力波对背景辐射各向异性的贡献．     

Inflation and the Cosmic Microwave Background

I give a status report and outlook concerning the use of the cosmic microwave background anisotropies to constrain the inflationary cosmology, and stress its crucial role as an underlying paradigm for the estimation of cosmological parameters. This revised version was published online in July 2006 with corrections to the Cover Date.     

星系团内物理过程对宇宙微波背景辐射的影响

观测表明,富星系团内存在着大量的高温热电子.它们将与微波背景光子相互作用.本文考虑了星系团集合使微波背景辐射产生的畸变.我们的理论估计表明,富星系团集合的高温热电子散射背景光子,使背景辐射谱偏离黑体辐射谱.在背景谱的维恩区,畸变小于2.74K黑体峰值强度的1％,这个结果与最近COBE卫星的探测结果是一致的.没有得到Matsumoto所探测到的在700μm附近有相当于黑体谱峰值强度10％的重大畸变.星系作为微引力透镜,对背景辐射的影响不可能探测得到.星系团内热电子的轫致辐射在微波波段更弱.     

Testing dark energy with the Advanced Liquid-mirror Probe of Asteroids, Cosmology and Astrophysics

The Advanced Liquid-mirror Probe of Asteroids, Cosmology and Astrophysics (ALPACA) is a proposed 8-m liquid-mirror telescope surveying  ∼1000 deg²  of the Southern hemisphere sky. It will be a remarkably simple and inexpensive telescope that none the less will deliver a powerful sample of optical data for studying dark energy. The bulk of the cosmological data consist of nightly, high signal-to-noise ratio, multiband light curves of Type Ia supernovae (SNe Ia). At the end of the 3-yr run, ALPACA is expected to collect  ≳100 000  SNe Ia up to   z ∼ 1  . This will allow us to reduce present systematic uncertainties affecting the standard-candle relation. The survey will also provide several other data sets such as the detection of baryon acoustic oscillations in the matter power spectrum and shear weak-lensing measurements. In this preliminary analysis, we forecast constraints on dark energy parameters from SNe Ia and baryon acoustic oscillations. The combination of these two data sets will provide competitive constraints on the dark energy parameters under minimal prior assumptions. Further studies are needed to address the accuracy of weak-lensing measurements.     

The frequency spectrum of the Cosmic Microwave Background

The status and the astrophysical implications of the search for deviations from a Planck distribution in the spectrum of the Cosmic Microwave Background are presented.     

Cosmic microwave background constraints on the epoch of reionization

We use a compilation of cosmic microwave anisotropy data to constrain the epoch of reionization in the Universe, as a function of cosmological parameters. We consider spatially flat cosmologies, varying the matter density Ω₀ (the flatness being restored by a cosmological constant), the Hubble parameter h and the spectral index n of the primordial power spectrum. Our results are quoted both in terms of the maximum permitted optical depth to the last-scattering surface, and in terms of the highest allowed reionization redshift assuming instantaneous reionization. For critical-density models, significantly tilted power spectra are excluded as they cannot fit the current data for any amount of reionization, and even scale-invariant models must have an optical depth to last scattering of below 0.3. For the currently favoured low-density model with Ω₀=0.3 and a cosmological constant, the earliest reionization permitted to occur is at around redshift 35, which roughly coincides with the highest estimate in the literature. We provide general fitting functions for the maximum permitted optical depth, as a function of cosmological parameters. We do not consider the inclusion of tensor perturbations, but if present they would strengthen the upper limits that we quote.     

Cosmic acceleration and extra dimensions: constraints on modifications of the Friedmann equation

An alternative to dark energy as an explanation for the present phase of accelerated expansion of the Universe is that the Friedmann equation is modified, e.g. by extra dimensional gravity, on large scales. We explore a natural parametrization of a general modified Friedmann equation, and find that the present supernova Type Ia and cosmic microwave background data prefer a correction of the form 1/ H to the Friedmann equation over a cosmological constant.     

Inhomogeneous Reionization and the Polarization of the Cosmic Microwave Background

In a universe with inhomogeneous reionization, the ionized patches create a second-order signal in the cosmic microwave background polarization anisotropy. This signal originates in the coupling of the free-electron fluctuation to the quadruple moment of the temperature anisotropy. We examine the contribution from a simple inhomogeneous reionization model and find that the signal from such a process is below the detectable limits of the Planck Surveyor mission. However, the signal is above the fundamental uncertainty limit from cosmic variance, so that a future detection with a high-accuracy experiment on subarcminute scales is possible.     

The spectrum of Cosmic Microwave Background at low frequency

The spectrum of Cosmic Microwave Background at frequency close or below 1 GHz is currently known with a large uncertainty. The difficulties arise both from the calibration technique and the presence of large foreground signals. In this spectral region large deviations from the Planck distribution are still permitted. In this paper the current status of our knowledge is described. Experiments involved and techniques employed are also discussed.     

Polarization of the Cosmic Microwave Background: the Milan Polarimeter Experiment

We describe a Two Channel Correlation Polarimeter built by the Milan Radio Group for searching polarization of the Cosmic Microwave Background. The system sensitivity is sufficient to detect linearly polarized signals or set firm upper limits at levels of few μK. The program of observations and some preliminary results are presented.     

Microwave background radiation related evidence in favour of the standard model

The discovery of the 3K microwave background radiation (MBR) and its interpretation as a relict of the hot big bang was probably the most important observation that led to the elevation of the hot big bang model to the status of a ‘Standard Model’. The temperature of this background is consistent with the primordial nucleosynthesis hypothesis. Detailed measurements of the spectrum and angular anisotropy of this radiation background have been found — within the measurement errors - to be consistent with the expectations of the Standard Model and with the formation of structure from the gravitational growth of primordial seed density perturbations within this framework.     

Large-Scale Motions in Superclusters: Their Imprint in the Cosmic Microwave Background

We study the spectral distortions of the cosmic microwave background radiation induced by the effect in clusters of galaxies when the target electrons have a modified Maxwell-Boltzmann distribution with a high-energy nonthermal tail. Bremsstrahlung radiation from this type of electron distribution may explain the suprathermal X-ray emission observed in some clusters such as the Coma Cluster and A2199 and serve as an alternative to the classical but problematic inverse Compton scattering interpretation. We show that the Sunyaev-Zeldovich effect can be used as a powerful tool to probe the electron distribution in clusters of galaxies and discriminate among these different interpretations of the X-ray excess. The existence of a nonthermal tail can have important consequences for cluster-based estimators of cosmological parameters.     

Time Variation of Cosmic and Quantum Masses in Dirac’s Cosmology

It is shown that the expressions of five fundamental masses appearing in physics and cosmology can be written in terms of the constants of nature. We study the time variation of them in the context of a generalized Dirac’s cosmology based on the large number hypothesis (LNH). This generalization allows one to have the gravitational constant not depending upon time contrary to Dirac’s original theory. It also allows the rest mass of the particle to vary with cosmological time. Further, we show that there exist simple algebraic relations between them and that their ratios can be expressed as powers of the large dimensionless number 10⁴⁰.     

Cosmic microwave background anisotropies resulting from feedback-regulated inhomogeneous reionization

We calculate the secondary anisotropies in the cosmic microwave background (CMB) produced by inhomogeneous reionization from simulations in which the effects of radiative and stellar feedback effects on galaxy formation have been included. This allows us to determine self-consistently the beginning ( z _i≈30), the duration ( δz ≈20) and the (non-linear) evolution of the reionization process for a critical density cold dark matter (CDM) model. In addition, from the simulated spatial distribution of ionized regions, we are able to calculate the evolution of the two-point ionization correlation function, C _χ , and obtain the power spectrum of the anisotropies, C _ℓ, in the range 5000<ℓ<10⁶. The power spectrum has a broad maximum around ℓ≈30 000, where it reaches the value 2×10⁻¹². We also show that the ionization correlation function C _χ is not Gaussian, but at separation angles θ ≲10⁻⁴ rad it can be approximated by a modified Lorentzian shape; at larger separations an anticorrelation signal is predicted for both C _χ and C ( θ ). Detection of signals as above will be possible with future millimetre-wavelength interferometers like the Atacama Large Millimeter Array (ALMA) , which appears as an optimum instrument to search for signatures of inhomogeneous reionization.