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.     

Possible connection between the location of the cutoff in the cosmic microwave background spectrum and the equation of state of dark energy

We investigate a possible connection between the suppression of the power at low multipoles in the cosmic microwave background (CMB) spectrum and the late time acceleration. We show that, assuming a cosmic IR/UV duality between the UV cutoff and a global infrared cutoff given by the size of the future event horizon, the equation of state of the dark energy can be related to the apparent cutoff in the CMB spectrum. The present limits on the equation of state of dark energy are shown to imply an IR cutoff in the CMB multipole interval of 9>l>8.5.     

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.     

Temperature effect on the power spectrum in inflation

We examine the effect of the thermal vacuum on the power spectrum of inflation by using the thermal field dynamics. We find that the thermal effect influences the CMB anisotropy at large length scale. After removing the divergence by using the holographic cutoff, we observe that the thermal vacuum explains well the observational CMB result at low multipoles. This shows that the temperature dependent factor should be considered in the study of power spectrum in inflation, especially at large length scale.     

Extragalactic contributions to the CMB signal

One of the main challenges facing upcoming Cosmic Microwave Background (CMB) experiments aiming at measuring temperature anisotropies with great accuracy will be to assess the contamination of CMB measurements by galactic and extragalactic foregrounds. On the extragalactic side, confusion noise from extragalactic sources hampers the detection of intrinsic CMB anisotropies at small angular scales. Secondary CMB anisotropies must also be carefully accounted for in order to isolate the primordial fluctuations. We present in this article a brief overview of the extragalactic contributions to the CMB. The galactic foregrounds are discussed elsewhere (Giard and Lagache, this issue). To cite this article: G. Lagache, N. Aghanim, C. R. Physique 4 (2003).     

Large angular scale CMB anisotropy from an excited initial mode

According to inflationary cosmology, the CMB anisotropy gives an opportunity to test predictions of new physics hypotheses. The initial state of quantum fluctuations is one of the important options at high energy scale, as it can affect observables such as the CMB power spectrum. In this study a quasi-de Sitter inflationary background with approximate de Sitter mode function built over the Bunch-Davies mode is applied to investigate the scale-dependency of the CMB anisotropy. The recent Planck constraint on spectral index motivated us to examine the effect of a new excited mode function(instead of pure de Sitter mode) on the CMB anisotropy at large angular scales. In so doing, it is found that the angular scale-invariance in the CMB temperature fluctuations is broken and in the limit 200 a tiny deviation appears. Also, it is shown that the power spectrum of CMB anisotropy is dependent on a free parameter with mass dimension H M* Mp and on the slow-roll parameter.     

New evidence for lack of CMB power on large scales

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.     

Effect on cosmic microwave background polarization of coupling of quintessence to pseudoscalar formed from the electromagnetic field and its dual

We present the full set of power spectra of cosmic microwave background (CMB) temperature and polarization anisotropies due to the coupling between quintessence and pseudoscalar of electromagnetism. This coupling induces a rotation of the polarization plane of the CMB, thus resulting in a nonvanishing B mode and parity-violating TB and EB modes. Using the BOOMERANG data from the flight of 2003, we derive the most stringent constraint on the coupling strength. We find that in some cases the rotation-induced B mode can confuse the hunting for the gravitational lensing-induced B mode.     

Quantum diffusion in polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate quantum diffusion of an electron in a model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with fluctuation of the parameters due to the impact of colored noise. The randomness is introduced by fluctuations of distance between two consecutive bases along the stacked base pairs. We demonstrate that in the model the decay time of the correlation can control the spread of the electronic wavepacket. Furthermore it is shown that in a motional narrowing regime the averaging over fluctuation causes ballistic propagation of the wavepacket, and in the adiabatic regime the electronic states are affected by localization.     

Primordial gravity waves and weak lensing

Inflation produces a primordial spectrum of gravity waves in addition to the density perturbations which seed structure formation. We compute the signature of these gravity waves in the large scale shear field. The shear can be divided into a gradient mode (G or E) and a curl mode (C or B). The latter is produced only by gravity waves, so the observations of a nonzero curl mode could be seen as evidence for inflation. We find that the expected signal from inflation is small, peaking on the largest scales at l(l+1)C(l)/2pi<10(-11) at l=2 and falling rapidly thereafter. Even for an all-sky deep survey, this signal would be below noise at all multipoles.     

Cosmic microwave background radiation anisotropies in brane worlds

We propose a new formulation to calculate the cosmic microwave background (CMB) spectrum in the Randall-Sundrum two-brane model based on recent progress in solving the bulk geometry using a low energy approximation. The evolution of the anisotropic stress imprinted on the brane by the 5D Weyl tensor is calculated. An impact of the dark radiation perturbation on the CMB spectrum is investigated in a simple model assuming an initially scale-invariant adiabatic perturbation. The dark radiation perturbation induces isocurvature perturbations, but the resultant spectrum can be quite different from the prediction of simple mixtures of adiabatic and isocurvature perturbations due to Weyl anisotropic stress.     

Measuring the small-scale power spectrum of cosmic density fluctuations through 21 cm tomography prior to the epoch of structure formation

The thermal evolution of the cosmic gas decoupled from that of the cosmic microwave background (CMB) at a redshift z approximately 200. Afterwards and before the first stars had formed, the cosmic neutral hydrogen absorbed the CMB flux at its resonant 21 cm spin-flip transition. We calculate the evolution of the spin temperature for this transition and the resulting anisotropies that are imprinted on the CMB sky due to linear density fluctuations during this epoch. These anisotropies, at an observed wavelength of 10.56[(1+z)/50] m, contain an amount of information that is orders of magnitude larger than any other cosmological probe.     

Mechanism for negative poisson ratios over the alpha- beta transition of cristobalite, SiO2: A molecular-dynamics study

The adiabatic elastic constants ( C(ij)) of cristobalite have been evaluated successfully over the temperature range of 300-1800 K using the molecular-dynamics method with a fluctuation formula. Cristobalite shows a negative Poisson ratio over this temperature range. However, the mechanisms differ between the alpha and beta phases. In the cubic beta phase, C44 exhibits a value extremely close to C11 rather than C12, in contrast to the Cauchy relation. This predicts a remarkable property that the longitudinal and transverse velocities coincide for the acoustic waves propagating along the [100] direction.     

Extensive Adiabatic Invariants for Nonlinear Chains

We look for extensive adiabatic invariants in nonlinear chains in the thermodynamic limit. Considering the quadratic part of the Klein-Gordon Hamiltonian, by a linear change of variables we transform it into a sum of two parts in involution. At variance with the usual method of introducing normal modes, our constructive procedure allows us to exploit the complete resonance, while keeping the extensive nature of the system. Next we construct a nonlinear approximation of an extensive adiabatic invariant for a perturbation of the discrete nonlinear Schrödinger model. The fluctuations of this quantity are controlled via Gibbs measure estimates independent of the system size, for a large set of initial data at low specific energy. Finally, by numerical calculations we show that our adiabatic invariant is well conserved for times much longer than predicted by our first order theory, with fluctuation much smaller than expected according to standard statistical estimates.     

Constraints on the extensions to the base ΛCDM model from BICEP2, Planck and WMAP

Recently Background Imaging of Cosmic Extragalactic Polarization(B2)discovered the relic gravitational waves at 7.0σconfidence level.However,the other cosmic microwave background(CMB)data,for example Planck data released in 2013(P13),prefer a much smaller amplitude of the primordial gravitational waves spectrum if a power-law spectrum of adiabatic scalar perturbations is assumed in the six-parameterΛCDM cosmology.In this paper,we explore whether the wCDM model and the running spectral index can relax the tension between B2 and other CMB data.Specifically we found that a positive running of running of spectral index is preferred at 1.7σlevel from the combination of B2,P13 and WMAP Polarization data.     

CMB polarization as complementary information to anisotropies

The origin of CMB polarization is reviewed. Special emphasis is placed on the cosmological information encoded in it: the nature of primordial fluctuations, the connection with the inflation paradigm. Insights into more recent epochs are also discussed: early reionization and high redshift matter distribution from CMB lensing. To cite this article: J. Kaplan et al., C. R. Physique 4 (2003).     

Additive noise-induced Turing transitions in spatial systems with application to neural fields and the Swift-Hohenberg equation

This work studies the spatio-temporal dynamics of a generic integral-differential equation subject to additive random fluctuations. It introduces a combination of the stochastic center manifold approach for stochastic differential equations and the adiabatic elimination for Fokker-Planck equations, and studies analytically the systems’ stability near Turing bifurcations. In addition two types of fluctuation are studied, namely fluctuations uncorrelated in space and time, and global fluctuations, which are constant in space but uncorrelated in time. We show that the global fluctuations shift the Turing bifurcation threshold. This shift is proportional to the fluctuation variance. Applications to a neural field equation and the Swift-Hohenberg equation reveal the shift of the bifurcation to larger control parameters, which represents a stabilization of the system. All analytical results are confirmed by numerical simulations of the occurring mode equations and the full stochastic integral-differential equation. To gain some insight into experimental manifestations, the sum of uncorrelated and global additive fluctuations is studied numerically and the analytical results on global fluctuations are confirmed qualitatively.     

QUANTUM FLUCTUATION OF THE ORDER PARAMETER AND THE OPTICAL ABSORPTION IN POLYACETYLENEO

We study in this paper the effects of lattice quantum fluctuations upon the order parametert in the Peierls systems by using the Green's function technique.We start from the discrete Su-Schrief fer-Heeger model with quantized phonon field and derive a coupled system of equations for the order parameter and Green's functions.It turns out that the order parameter is reduced compared with the adiabatic value but the Peierls instability survives the quantum fluctuations in agreement with,Monte Carlo results.The band-to-band optical absorption coefficient of polyacetylene with lattice fluctuation being accounted for is also calculated and compared with the experimental data.     

Do baryons trace dark matter in the early universe?

Baryon-density perturbations of large amplitude may exist if they are compensated by dark-matter perturbations such that the total density is unchanged. Primordial abundances and galaxy clusters allow these compensated isocurvature perturbations (CIPs) to have amplitudes as large as ~10%. CIPs will modulate the power spectrum of cosmic microwave background (CMB) fluctuations--those due to the usual adiabatic perturbations--as a function of position on the sky. This leads to correlations between different spherical-harmonic coefficients of the temperature and/or polarization maps, and induces polarization B modes. Here, the magnitude of these effects is calculated and techniques to measure them are introduced. While a CIP of this amplitude can be probed on large scales with existing data, forthcoming CMB experiments should improve the sensitivity to CIPs by at least an order of magnitude.