Seven-year Wilkinson Microwave Anisotropy Probe Research Articles

A MEASUREMENT OF THE COSMIC MICROWAVE BACKGROUND DAMPING TAIL FROM THE 2500-SQUARE-DEGREE SPT-SZ SURVEY

We present a measurement of the cosmic microwave background (CMB) temperature power spectrum using data from the recently completed South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. This measurement is made from observations of 2540 deg$^2$ of sky with arcminute resolution at $150\,$GHz, and improves upon previous measurements using the SPT by tripling the sky area. We report CMB temperature anisotropy power over the multipole range $650<\ell<3000$. We fit the SPT bandpowers, combined with the seven-year Wilkinson Microwave Anisotropy Probe (WMAP7) data, with a six-parameter LCDM cosmological model and find that the two datasets are consistent and well fit by the model. Adding SPT measurements significantly improves LCDM parameter constraints; in particular, the constraint on $\theta_s$ tightens by a factor of 2.7. The impact of gravitational lensing is detected at $8.1\, \sigma$, the most significant detection to date. This sensitivity of the SPT+WMAP7 data to lensing by large-scale structure at low redshifts allows us to constrain the mean curvature of the observable universe with CMB data alone to be $\Omega_k=-0.003^{+0.014}_{-0.018}$. Using the SPT+WMAP7 data, we measure the spectral index of scalar fluctuations to be $n_s=0.9623 \pm 0.0097$ in the LCDM model, a $3.9\,\sigma$ preference for a scale-dependent spectrum with $n_s<1$. The SPT measurement of the CMB damping tail helps break the degeneracy that exists between the tensor-to-scalar ratio $r$ and $n_s$ in large-scale CMB measurements, leading to an upper limit of $r<0.18$ (95%,C.L.) in the LCDM+$r$ model. Adding low-redshift measurements of the Hubble constant ($H_0$) and the baryon acoustic oscillation (BAO) feature to the SPT+WMAP7 data leads to further improvements. The combination of SPT+WMAP7+$H_0$+BAO constrains $n_s=0.9538 \pm 0.0081$ in the LCDM model, a $5.7\,\sigma$ detection of $n_s < 1$, ... [abridged]

Tachyon-polytropic inflation on the brane

Abstract We consider the tachyon-brane inflationary universe model in the context of a polytropic gas equation of state. In slow-roll approximation, we discuss general conditions of this model. For exponential potential, in high-energy limit the characteristics of the model are presented. By using the seven-year Wilkinson Microwave Anisotropy Probe (WMAP7) observational data, we constrain the cosmological parameters of the model.

Cosmological perturbations in warm-tachyon inflationary universe model with viscous pressure on the brane

We study warm-viscous inflationary universe model on the brane, in a tachyon field theory. We obtain the general conditions which are required for this model to be realizable. In longitudinal gauge, the primoradial perturbation parameters are found in great details, using slow-roll and quasi-stable approximations. The general expressions of the tensor-to-scalar ratio, scalar spectral index and its running are found. We derive the characteristics of the inflationary universe model by using an effective exponential potential in two cases: 1- Dissipative parameter $\Gamma$ and bulk viscous parameter $\zeta$ are constant parameters. 2- Dissipative parameter as a function of tachyon field $\phi$ and bulk viscous parameter as a function of radiation-matter mixture energy density $\rho$. The parameters of the model are restricted by recent observational data from the seven-year Wilkinson microwave anisotropy probe (WMAP7).

First measurement of the bulk flow of nearby galaxies using the cosmic microwave background

Peculiar velocities in the nearby Universe can be measured via the kinetic Sunyaev-Zel'dovich (kSZ) effect. Using a statistical method based on an optimised cross-correlation with nearby galaxies, we extract the kSZ signal generated by plasma halo of galaxies from the Cosmic Microwave Background (CMB) temperature anisotropies observed by the Wilkinson Microwave Anisotropy Probe (WMAP). Marginalising over the thermal Sunyaev-Zel'dovich contribution from clusters of galaxies, possible unresolved point source contamination, and Galactic foregrounds (dust, synchrotron and free-free emission), we report a kSZ bulk flow signal present at the 90% confidence level in the seven-year WMAP data. When only galaxies within 50 Mpc/h are included in the kSZ template we find a bulk flow in the CMB frame of |V|=533 +/- 263 km/s, in the direction l=324 +/- 27, b=-7 +/- 17, consistent with bulk flow measurements on a similar scale using classical distance indicators. We show how this comparison constrains the (ionised) baryonic budget in the local universe. On very large (~ 500 Mpc/h) scales, we find a 95% upper limit of 470 km/s, inconsistent with some analyses of bulk flow of clusters from the kSZ. We estimate that the significance of the bulk flow signal may increase to 3-5 sigma using data from the PLANCK probe.

COSMOLOGICAL CONSTRAINTS FROM SUNYAEV–ZEL'DOVICH-SELECTED CLUSTERS WITH X-RAY OBSERVATIONS IN THE FIRST 178 deg2 OF THE SOUTH POLE TELESCOPE SURVEY

We use measurements from the South Pole Telescope (SPT) Sunyaev–Zel'dovich (SZ) cluster survey in combination with X-ray measurements to constrain cosmological parameters. We present a statistical method that fits for the scaling relations of the SZ and X-ray cluster observables with mass while jointly fitting for cosmology. The method is generalizable to multiple cluster observables, and self-consistently accounts for the effects of the cluster selection and uncertainties in cluster mass calibration on the derived cosmological constraints. We apply this method to a data set consisting of an SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg2 of the 2500 deg2 SPT-SZ survey, with 14 clusters having X-ray observations from either Chandra or XMM-Newton. Assuming a spatially flat ΛCDM cosmological model, we find the SPT cluster sample constrains σ8(Ωm/0.25)0.30 = 0.785 ± 0.037. In combination with measurements of the cosmic microwave background (CMB) power spectrum from the SPT and the seven-year Wilkinson Microwave Anisotropy Probe data, the SPT cluster sample constrains σ8 = 0.795 ± 0.016 and Ωm = 0.255 ± 0.016, a factor of 1.5 improvement on each parameter over the CMB data alone. We consider several extensions beyond the ΛCDM model by including the following as free parameters: the dark energy equation of state (w), the sum of the neutrino masses (Σmν), the effective number of relativistic species (Neff), and a primordial non-Gaussianity (fNL). We find that adding the SPT cluster data significantly improves the constraints on w and Σmν beyond those found when using measurements of the CMB, supernovae, baryon acoustic oscillations, and the Hubble constant. Considering each extension independently, we best constrain w = −0.973 ± 0.063 and the sum of neutrino masses Σmν < 0.28 eV at 95% confidence, a factor of 1.25 and 1.4 improvement, respectively, over the constraints without clusters. Assuming a ΛCDM model with a free Neff and Σmν, we measure Neff = 3.91 ± 0.42 and constrain Σmν < 0.63 eV at 95% confidence. We also use the SPT cluster sample to constrain fNL = −220 ± 317, consistent with zero primordial non-Gaussianity. Finally, we discuss the current systematic limitations due to the cluster mass calibration, and future improvements for the recently completed 2500 deg2 SPT-SZ survey. The survey has detected ∼500 clusters with a median redshift of ∼0.5 and a median mass of ∼2.3 × 1014 M☉ h−1 and, when combined with an improved cluster mass calibration and existing external cosmological data sets will significantly improve constraints on w.

INFLATION AND ACCELERATING UNIVERSE IN MODIFIED MODULAR INVARIANT SUPERGRAVITY

A method of explaining the recently observed acceleration of cosmic expansion as well as inflation in the early universe is presented within the same framework. The goal is to construct an inflation model based on supergravity and the slow-roll approximation (SRA) that both satisfactorily predicts observed inflationary parameters and at the same time explains the accelerated expansion of the universe. The model is based on a modification of string-based modular invariant supergravity previously proposed by the present authors. It realizes slow-roll inflation in the Einstein frame and is successful in explaining Wilkinson Microwave Anisotropy Probe (WMAP) observational data, through fine-tuning procedure of free parameters. The parameter dependence of the model is considered in detail in order to determine the range for which the SRA can be applied. Within the allowed range of parameter values, a vacuum energy of ~10-120 can be obtained, which coincides with the cosmological constant, and can play the role of dark energy in the universe. The calculated inflationary parameters fit very well to seven-year WMAP data. The ratio of the scalar and tensor power spectra is predicted to be r ~6.8 ×10-2, and this may soon be verified by observations by the Planck satellite. The non-Gaussianity parameter fNL is also estimated by the slow-roll parameters.

Revisiting Cardassian model and cosmic constraint

In this paper, we revisit the Cardassian model in which the radiation energy component is included. It is important for early epoch when the radiation cannot be neglected because the equation of state (EoS) of the effective dark energy becomes time variable. Therefore, it is not equivalent to the quintessence model with a constant EoS anymore. This situation was almost overlooked in the literature. By using the recent released Union2 557 of type Ia supernovae (SN Ia), the baryon acoustic oscillation (BAO) from Sloan Digital Sky Survey and the WiggleZ data points, the full information of cosmic microwave background (CMB) measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observation, we constrain the Cardassian model via the Markov Chain Monte Carlo (MCMC) method. A tight constraint is obtained: $n= -0.0479_{- 0.0732- 0.148}^{+ 0.0730+ 0.142}$ in $1,2\sigma$ regions. The deviation of Cardassian model from quintessence model is shown in CMB anisotropic power spectra at high l's parts due to the evolution of EoS. But it is about the order of 0.1% which cannot be discriminated by current data sets. The Cardassian model is consistent with current cosmic observational data sets.

Constraint on the primordial vector mode and its magnetic field generation from seven-year Wilkinson Microwave Anisotropy Probe observations

It is often stated that the cosmological vector mode has only a decaying mode and gives negligible effects on cosmological observations. The vector mode, however, has a growing mode if there exists anisotropic stress in energy distributions in the universe. In this paper, we consider a primordial vector mode sustained by free-streaming neutrinos and its associated magnetic field generation. First, we put an observational constraint on the amount of the vector mode from the 7-year WMAP data. The constraint is found as ${r}_{v}\ensuremath{\lesssim}\ensuremath{-}\frac{r}{40}+0.012$, where ${r}_{v}$ and $r$ are the amounts of vector and tensor perturbation amplitudes with respect to the scalar one, respectively. Second, we calculate the spectrum of magnetic fields inevitably created from the primordial vector mode, given the constraint on ${r}_{v}$. It is found that the maximum amount of magnetic fields generated from the vector mode is given by $B\ensuremath{\lesssim}{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{G}(\frac{{r}_{v}}{0.012}{)}^{1/2}(\frac{k}{0.002}{)}^{({n}_{v}+1)/2}$, with ${n}_{v}$ being a spectral index of the vector mode. We find a nontrivial cancellation of the magnetic field generation in the radiation-dominated era, which creates a characteristic cutoff in the magnetic field spectrum around $k\ensuremath{\approx}1.0\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$.

A MEASUREMENT OF THE DAMPING TAIL OF THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM WITH THE SOUTH POLE TELESCOPE

We present a measurement of the angular power spectrum of the cosmic microwave background (CMB) using data from the South Pole Telescope (SPT). The data consist of 790 square degrees of sky observed at 150 GHz during 2008 and 2009. Here we present the power spectrum over the multipole range 650 < ell < 3000, where it is dominated by primary CMB anisotropy. We combine this power spectrum with the power spectra from the seven-year Wilkinson Microwave Anisotropy Probe (WMAP) data release to constrain cosmological models. We find that the SPT and WMAP data are consistent with each other and, when combined, are well fit by a spatially flat, LCDM cosmological model. The SPT+WMAP constraint on the spectral index of scalar fluctuations is ns = 0.9663 +/- 0.0112. We detect, at ~5-sigma significance, the effect of gravitational lensing on the CMB power spectrum, and find its amplitude to be consistent with the LCDM cosmological model. We explore a number of extensions beyond the LCDM model. Each extension is tested independently, although there are degeneracies between some of the extension parameters. We constrain the tensor-to-scalar ratio to be r < 0.21 (95% CL) and constrain the running of the scalar spectral index to be dns/dlnk = -0.024 +/- 0.013. We strongly detect the effects of primordial helium and neutrinos on the CMB; a model without helium is rejected at 7.7-sigma, while a model without neutrinos is rejected at 7.5-sigma. The primordial helium abundance is measured to be Yp = 0.296 +/- 0.030, and the effective number of relativistic species is measured to be Neff = 3.85 +/- 0.62. The constraints on these models are strengthened when the CMB data are combined with measurements of the Hubble constant and the baryon acoustic oscillation feature. Notable improvements include ns = 0.9668 +/- 0.0093, r < 0.17 (95% CL), and Neff = 3.86 +/- 0.42. The SPT+WMAP data show...

Latest cosmological constraints on Cardassian expansion models including the updated gamma-ray bursts

We constrain the Cardassian expansion models from the latest observations, including the updated Gamma-ray bursts (GRBs), which are calibrated using a cosmology independent method from the Union2 compilation of type Ia supernovae (SNe Ia). By combining the GRB data with the joint observations from the Union2 SNe Ia set, along with the results from the Cosmic Microwave Background radiation observation from the seven-year Wilkinson Microwave Anisotropy Probe and the baryonic acoustic oscillation observation galaxy sample from the spectroscopic Sloan Digital Sky Survey Data Release, we find significant constraints on the model parameters of the original Cardassian model ΩM0 = 0.282+0.015−0.014, n = 0.03+0.05−0.05; and n = −0.16+0.25−3.26, β = 0.76+0.34−0.58 of the modified polytropic Cardassian model, which are consistent with the ΛCDM model in a 1-σ confidence region. From the reconstruction of the deceleration parameter q(z) in Cardassian models, we obtain the transition redshift zT = 0.73 ± 0.04 for the original Cardassian model and zT = 0.68 ± 0.04 for the modified polytropic Cardassian model.

Observational constraints on exponential gravity

We study the observational constraints on the exponential gravity model of $f(R)=\ensuremath{-}\ensuremath{\beta}{R}_{s}(1\ensuremath{-}{e}^{\ensuremath{-}R/{R}_{s}})$. We use the latest observational data including Supernova Cosmology Project Union2 compilation, Two-Degree Field Galaxy Redshift Survey, Sloan Digital Sky Survey Data Release 7, and Seven-Year Wilkinson Microwave Anisotropy Probe in our analysis. From these observations, we obtain a lower bound on the model parameter $\ensuremath{\beta}$ at 1.27 (95% C.L.) but no appreciable upper bound. The constraint on the present matter density parameter is $0.245&lt;{\ensuremath{\Omega}}_{m}^{0}&lt;0.311$ (95% C.L.). We also find out the best-fit value of model parameters on several cases.

Cosmic constraint to DGP brane model: Geometrical and dynamical perspectives

In this paper, the Dvali-Gabadadze-Porrati (DGP) brane model is confronted by current cosmic observational data sets from geometrical and dynamical perspectives. On the geometrical side, the recently released Union2 557 of type Ia supernovae (SN Ia), the baryon acoustic oscillation from the Sloan Digital Sky Survey and the Two Degree Galaxy Redshift Survey (transverse and radial to line-of-sight data points), the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations [shift parameters $R$, ${l}_{a}({z}_{*})$ and redshift at the last scatter surface ${z}_{*}$], ages of high redshifts galaxies, i.e., the lookback time and the high redshift gamma ray bursts are used. On the dynamical side, data points about the growth function of matter linear perturbations are used. Using the same data set combination, we also constrain the flat $\ensuremath{\Lambda}\mathrm{CDM}$ model as a comparison. The results show that current geometrical and dynamical observational data sets much favor the flat $\ensuremath{\Lambda}\mathrm{CDM}$ model and the departure from it is above $4\ensuremath{\sigma}(6\ensuremath{\sigma})$ for the spatially flat DGP model with (without) SN systematic errors. The consistence of growth function data points is checked in terms of a relative departure of redshift-distance relation.

Comparison of dark energy models: A perspective from the latest observational data

In this paper, we compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of $H_0$ from the Hubble Space Telescope. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data. For other dynamical dark energy models, we find that some of them, such as the $\alpha$ dark energy, constant $w$, generalized Chaplygin gas, Chevalliear-Polarski-Linder parametrization, and holographic dark energy models, can provide good fits to the current data, and three of them, namely, the Ricci dark energy, agegraphic dark energy, and Dvali-Gabadadze-Porrati models, are clearly disfavored by the data.