Constraining cosmological parameters through Sunyaev-Zel’dovich surveys

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.     

Position-space description of the cosmic microwave background and its temperature correlation function

We suggest that the cosmic microwave background (CMB) temperature correlation function C(theta) as a function of angle provides a direct connection between experimental data and the fundamental cosmological quantities. The evolution of inhomogeneities in the prerecombination universe is studied using Green's functions in position space. We find that a primordial adiabatic point perturbation propagates as a sharp-edged spherical acoustic wave. Density singularities at its wave fronts create a feature in the CMB correlation function distinguished by a dip at theta approximately 1.2 degrees. Characteristics of the feature are sensitive to the values of cosmological parameters, in particular to the total and the baryon densities.     

Cosmology with cosmic microwave background anisotropy

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.     

Inflation,quantum fields,and CMB anisotropies

Inflationary cosmology has proved to be the most successful at predicting the properties of the anisotropies observed in the cosmic microwave background (CMB). In this essay we show that quantum field renormalization significantly influences the generation of primordial perturbations and hence the expected measurable imprint of cosmological inflation on the CMB. However, the new predictions remain in agreement with observation, and in fact favor the simplest forms of inflation. In the near future, observations of the influence of gravitational waves from the early universe on the CMB will test our new predictions.     

A Quantum Mechanical Relation Connecting Time,Temperature, and Cosmological Constant of the Universe: Gamow’S Relation Revisited as a Special Case

Considering our expanding universe as made up of gravitationally interacting particles which describe particles of luminous matter, dark matter and dark energy which is represented by a repulsive harmonic potential among the points in the flat 3-space and incorporating Mach’s principle into our theory, we derive a quantum mechanical relation connecting, temperature of the cosmic microwave background radiation, age, and cosmological constant of the universe. When the cosmological constant is zero, we get back Gamow’s relation with a much better coefficient. Otherwise, our theory predicts a value of the cosmological constant 2.0×10⁻⁵⁶ cm⁻² when the present values of cosmic microwave background temperature of 2.728 K and age of the universe 14 billion years are taken as input.     

CMB: the isotropic part

The Cosmic Microwave Background, or CMB, is the only truly diffuse background, whereas the other backgrounds come from the integrated light (along the line of sight) of various sources. The CMB is now known, thanks to the FIRAS experiment above the COBE satellite, to have a nearly perfect blackbody spectrum. This proves to be quite constraining on early energy releases. We review the average spectrum of the CMB with respect to other backgrounds and the consequences regarding the history of the early Universe. To cite this article: F.R. Bouchet, J.-L. Puget, C. R. Physique 4 (2003).     

Living with lambda

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.     

Is the evidence for dark energy secure?

Several kinds of astronomical observations, interpreted in the framework of the standard Friedmann–Robertson–Walker cosmology, have indicated that our universe is dominated by a Cosmological Constant. The dimming of distant Type Ia supernovae suggests that the expansion rate is accelerating, as if driven by vacuum energy, and this has been indirectly substantiated through studies of angular anisotropies in the cosmic microwave background (CMB) and of spatial correlations in the large-scale structure (LSS) of galaxies. However there is no compelling direct evidence yet for (the dynamical effects of) dark energy. The precision CMB data can be equally well fitted without dark energy if the spectrum of primordial density fluctuations is not quite scale-free and if the Hubble constant is lower globally than its locally measured value. The LSS data can also be satisfactorily fitted if there is a small component of hot dark matter, as would be provided by neutrinos of mass ∼0.5 eV. Although such an Einstein–de Sitter model cannot explain the SNe Ia Hubble diagram or the position of the “baryon acoustic oscillation” peak in the autocorrelation function of galaxies, it may be possible to do so, e.g. in an inhomogeneous Lemaitre–Tolman–Bondi cosmology where we are located in a void which is expanding faster than the average. Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model, rather than having physical reality.     

Signatures in the angular power spectrum of the cosmic microwave background anisotropies: Topological defect scenarios versus inflationary models

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.     

第一讲微波背景辐射的各向异性、偏振及宇宙电离的历史

文章对微波背景辐射的各向异性、偏振及宇宙电离的历史给出了评述性介绍．从大爆炸理论的预言，到观测的发现，到其各向异性及偏振的探测，微波背景辐射(CMB)向人们揭示了丰富的宇宙学信息．文章在对基本理论作了简单介绍后，着重讲述了最新的CMB的观测结果及其物理意义．特别对微波背景各向异性探测器(Wilkinson Microwave Anisotropy Probe，WMAP)的偏振观测及其对宇宙重新电离的限制给出了较详细的叙述．     

The return of a static universe and the end of cosmology

We demonstrate that as we extrapolate the current ΛCDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our “island universe” will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented. Fifth Award in the 2007 Essay Competition of the Gravity Research Foundation.     

Stimulated creation of quanta during inflation and the observable universe

Inflation provides a natural mechanism to account for the origin of cosmic structures. The generation of primordial inhomogeneities during inflation can be understood via the spontaneous creation of quanta from the vacuum. We show that when the corresponding stimulated creation of quanta is considered, the characteristics of the state of the universe at the onset of inflation are not diluted by the inflationary expansion and can be imprinted in the spectrum of primordial inhomogeneities. The non-gaussianities (particularly in the so-called squeezed configuration) in the cosmic microwave background and galaxy distribution can then tell us about the state of the universe that existed at the time when quantum field theory in curved spacetime first emerged as a plausible effective theory.     

Cosmological constraints on unparticle dark matter

In unparticle dark matter (unmatter) models, the equation of state of the unmatter is given by p=ρ/(2d _U+1), where d _U is the scaling factor. Unmatter with such equations of state would have a significant impact on the history of the expansion of the universe. Using type Ia supernovae (SNIa), the baryon acoustic oscillation (BAO) measurements and the shift parameter of the cosmic microwave background (CMB) to place constraints on such unmatter models, we find that if only the SNIa data are used, the constraints are weak. However, with the BAO and CMB shift parameter data added, strong constraints can be obtained. For the ΛUDM model, in which unmatter is the sole dark matter, we find that d _U>60 at 95% C.L. For comparison, in most unparticle physics models it is assumed that d _U<2. For the ΛCUDM model, in which unmatter co-exists with cold dark matter, we found that the unmatter can at most make up a few percent of the total cosmic density if d _U<10; thus it cannot be the major component of dark matter.     

Tetrad formalism and reference frames in general relativity

This review is devoted to problems of defining the reference frames in the tetrad formalism of General Relativity. Tetrads are the expansion coefficients of components of an orthogonal basis over the differentials of a coordinate space. The Hamiltonian cosmological perturbation theory is presented in terms of these invariant differential forms. This theory does not contain the double counting of the spatial metric determinant in contrast to the conventional Lifshits-Bardeen perturbation theory. We explicitly write out the Lorentz transformations of the orthogonal-basis components from the cosmic microwave background (CMB) reference frame to the laboratory frame, moving with a constant velocity relative to the CMB frame. Possible observational consequences of the Hamiltonian cosmological perturbation theory are discussed, in particular, the quantum anomaly of geometric interval and the shift of the origin, as a source of the CMB anisotropy, in the course of the universe evolution.     

One-loop effective action for non-local modified Gauss–Bonnet gravity in de Sitter space

We discuss the classical and quantum properties of non-local modified Gauss–Bonnet gravity in de Sitter space, using its equivalent representation via string-inspired local scalar-Gauss–Bonnet gravity with a scalar potential. A classical, multiple de Sitter universe solution is found where one of the de Sitter phases corresponds to the primordial inflationary epoch, while the other de Sitter space solution—the one with the smallest Hubble rate—describes the late-time acceleration of our universe. A Chameleon scenario for the theory under investigation is developed, and it is successfully used to show that the theory complies with gravitational tests. An explicit expression for the one-loop effective action for this non-local modified Gauss–Bonnet gravity in the de Sitter space is obtained. It is argued that this effective action might be an important step towards the solution of the cosmological constant problem.     

Gauge fields and inflation

The isotropy and homogeneity of the cosmic microwave background (CMB) favors “scalar driven” early Universe inflationary models. However, gauge fields and other non-scalar fields are far more common at all energy scales, in particular at high energies seemingly relevant to inflation models. Hence, in this review we consider the role and consequences, theoretical and observational, that gauge fields can have during the inflationary era. Gauge fields may be turned on in the background during inflation, or may become relevant at the level of cosmic perturbations. There have been two main classes of models with gauge fields in the background, models which show violation of the cosmic no-hair theorem and those which lead to isotropic FLRW cosmology, respecting the cosmic no-hair theorem. Models in which gauge fields are only turned on at the cosmic perturbation level, may source primordial magnetic fields. We also review specific observational features of these models on the CMB and/or the primordial cosmic magnetic fields. Our discussions will be mainly focused on the inflation period, with only a brief discussion on the post inflationary (p)reheating era.     

The imprint of inflation on the cosmic microwave background

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.     

A built-in scale in the initial spectrum of density perturbations: Evidence from cluster and CMB data

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.     

The Szekeres Swiss Cheese model and the CMB observations

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.