Wilkinson Microwave Anisotropy Probe Data Research Articles

Bianchi VIIhmodels and the cold spot texture

We have returned to our previous Bianchi VII h analysis in light of the Cruz et al. suggestion that the cold spot observed near the Southern Galactic Pole may be a remnant temperature perturbation of a cosmic texture. Bridges et al. used two favoured left-handed Bianchi VII h templates with restricted prior probabilities so that the template was centred close to the cold spot. Using Wilkinson Microwave Anisotropy Probe (WMAP) data 'corrected' for the texture fit we have now re-examined both models to assess any changes to these conclusions. We find that both models are left almost entirely unconstrained by the data and consequently exhibit significantly reduced Bayesian evidences. Both models are now disfavoured by the data. This result reinforces our previous assertion that the cold spot was significant in the detection of a Bianchi VII h component.

Constraints on kinetically modified inflation from WMAP5

Single field inflationary models with a non-minimal kinetic term (also called k-inflationary models) can be characterised by the so-called sound flow functions, which complete the usual Hubble flow hierarchy. These parameters appear in the primordial power spectra of cosmological perturbations at leading order and, therefore, affect the resulting Cosmic Microwave Background (CMB) anisotropies. Using the fifth year Wilkinson Microwave Anisotropy Probe (WMAP5) data, we derive the marginalised posterior probability distributions for both the sound and Hubble flow parameters. In contrast to the standard situation, these parameters remain separately unbounded, and notably there is no longer any upper limit on epsilon_1, the first Hubble flow function. Only special combinations of these parameters, corresponding to the spectral index and tensor-to-scalar ratio observables, are actually constrained by the data. The energy scale of k-inflation is nevertheless limited from above to Hinf/mpl < 6x10^(-6) at two-sigma level. Moreover, for the sub-class of Dirac-Born-Infeld models, by considering the non-gaussianity bounds on the sound speed, we find a weak limit epsilon_1 < 0.08 at 95% confidence level. Comment: 7 pages, 6 figures, uses RevTeX

Foreground analysis of theWilkinson Microwave Anisotropy Probe3-yr data with fastica

We present an analysis of the foreground emission present in the Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr data as determined by the method of Independent Component Analysis. The WMAP data averaged at each frequency are used together with the standard foreground emission templates as inputs to the fastica algorithm. The returned coefficients can be interpreted as coupling coefficients between the WMAP data and foreground templates. These results are then used to infer the spectral behaviour for three foreground components – synchrotron, anomalous dust-correlated emission and free–free. For the first two components, we find values consistent with previous results although slightly steeper. We confirm the inconsistency in the scaling between the Hα template and free–free emission at K and Ka bands where an electron temperature of ∼4000 K is indicated. We also see evidence of significantly flatter spectral behaviour to higher frequencies than expected theoretically and previously noted by Dobler et al., but only when analysing the Kp2 sky coverage. We further apply fastica‘iteratively’, using data pre-cleaned using foreground templates scaled to the WMAP frequencies by coupling coefficients determined by a prior fastica analysis. This multifrequency analysis allows us to determine the presence of residual foreground emission not traced by the templates. We confirm the existence of a component spatially distributed along the Galactic plane and particularly enhanced near the centre (the ‘WMAP haze’). This emission is less extended when using the WMAPK-Ka data as the synchrotron template confirming that it can be considered a better template for foreground cleaning of the WMAP data. However, its use complicates the physical interpretation of the nature of the foreground emission and residuals since it contains a mixture of several, physically distinct emission mechanisms. The good agreement between the extracted cosmic microwave background (CMB) component and previous results, as well as the low amplitude of residual foreground emission make fastica a viable tool to infer foreground emission properties, via template fitting, and the CMB amplitude.

Can a primordial magnetic field originate large-scale anomalies inWMAPdata?

Several accurate analyses of the cosmic microwave background (CMB) temperature maps from the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed a set of anomalous results, at large angular scales, that appears inconsistent with the statistical isotropy expected in the concordance cosmological model Λcold dark matter. Because these anomalies seem to indicate a preferred direction in the space, here we investigate the signatures that a primordial magnetic field, possibly present in the photon–baryon fluid during the decoupling era, could have produced in the large-angle modes of the observed CMB temperature fluctuations maps. To study these imprints, we simulate Monte Carlo CMB maps, which are statistically anisotropic due to the correlations between CMB multipoles induced by the magnetic field. Our analyses reveal the presence of the north–south angular correlations asymmetry phenomenon in these Monte Carlo maps, and we use these information to establish the statistical significance of such phenomenon observed in WMAP maps. Moreover, because a magnetic field produces planarity in the low-order CMB multipoles, where the planes are perpendicular to the preferred direction defined by the magnetic field, we investigate the possibility that two CMB anomalous phenomena, namely the north–south asymmetry and the quadrupole–octopole planes alignment, could have a common origin. Our results, for large angles, show that the correlations between low-order CMB multipoles introduced by a sufficiently intense magnetic field, can reproduce some of the large-angle anisotropic features mapped in WMAP data. We also reconfirm, at more than 95 per cent CL, the existence of a north–south power asymmetry in the WMAP 5-yr data.

Anomalous CMB north-south asymmetry

Several accurate analyses have revealed a statistically significant north-south ecliptic asymmetry in the large-angle correlations strength of the cosmic microwave background (CMB) radiation temperature field data from the Wilkinson Microwave Anisotropy Probe (WMAP). This asymmetry is inconsistent with the statistical isotropy expected in the concordance cosmological model $\ensuremath{\Lambda}\mathrm{CDM}$. It has been suggested that a possible cause-effect relationship exists between this large-angle anisotropy and the anomalous CMB quadrupole-octopole planes alignment. In turn, this later phenomenon (or both) would be a consequence of one or more of the following undesired effects in CMB data: a systematic error in the data processing or in the instrument characterization, residual foregrounds, and large-angle correlations induced by the incomplete sky CMB data (cut-sky masks are needed to reject galactic foregrounds). Here, it is proved that the north-south asymmetry is unrelated to the quadrupole ($\ensuremath{\ell}=2$) and the octopole ($\ensuremath{\ell}=3$) properties because we find, at high confidence levels, such large-angle anisotropy in three- and five-year WMAP CMB maps containing only the multipole components $4\ensuremath{\le}\ensuremath{\ell}\ensuremath{\le}10$. The statistical significance depends on both, the CMB map analyzed as well as the cut-sky mask applied to exclude foregrounds. In general, we obtain that the significance level of the north-south asymmetry is less in five-year WMAP data with KQ75 ($\ensuremath{\gtrsim}90%\text{ }\text{ }\mathrm{CL}$) than it is in three-year data with Kp0 ($\ensuremath{\gtrsim}96%\text{ }\text{ }\mathrm{CL}$). For instance, in the WMAP internal linear combination (ILC)-five-year map with the KQ75 mask (a sky cut of 28.4%) this phenomenon is observed at 92.7% CL, whereas for the WMAP ILC-three-year map with the Kp0 mask (a sky cut of 23.5%) this phenomenon appears at 96.5% CL. Moreover, it is also shown that this hemispherical asymmetry is unlikely due to systematics or foreground contaminants, because it is present in single-frequency, multifrequency, and cleaned ILC-type CMB maps. Additionally, robustness tests show that the statistical significance of the north-south asymmetry is affected by the use of the KQ85 and KQ75 masks in five-year single-frequency WMAP CMB maps, whereas it is insensitive with respect to application of the Kp2 and Kp0 masks in three-year single-frequency WMAP CMB maps. The confidence levels were obtained using sets of Monte Carlo CMB maps produced according to the $\ensuremath{\Lambda}\mathrm{CDM}$ model.

Looking for the Sunyaev-Zel'dovich effect in the Virgo cluster from WMAP and ROSAT data

Wilkinson Microwave Anisotropy Probe (WMAP) observations at millimetre wavelengths are sensitive to the Sunyaev–Zel’dovich (SZ) effect in galaxy clusters. Among all the objects in the sky, the Virgo cluster is expected to provide the largest integrated signal. Based on models compatible with the X-ray emission observed in the ROSAT All-Sky Survey, we predict an approximately 2σ detection of the SZ effect from Virgo in the WMAP 3-yr data. Our analysis reveals a 3σ signal on scales of 5 ◦ , although the frequency dependence deviates from the theoretical expectation for the SZ effect. The main sources of uncertainty are instrumental noise, and, most importantly, possible contamination from point sources and diffuse back/foregrounds. In particular, a population of unresolved extragalactic sources in Virgo would explain the observed intensity and frequency dependence. In order to resolve this question, one needs to wait for experiments like Planck to achieve the required accuracy.

A high-significance detection of non-Gaussianity in theWMAP5-yr data using directional spherical wavelets

We repeat the directional spherical real Morlet wavelet analysis, used previously to detect non-Gaussianity in the Wilkinson Microwave Anisotropy Probe (WMAP) 1- and 3-yr data, on the WMAP 5-yr data. The non-Gaussian signal detected previously is present in the 5-yr data at a slightly increased statistical significance of approximately 99 per cent. Localized regions that contribute most strongly to the non-Gaussian signal are found to be very similar to those detected in the previous releases of the WMAP data. When the localized regions detected in the 5-yr data are excluded from the analysis, the non-Gaussian signal is eliminated.

Real space tests of the statistical isotropy and Gaussianity of the Wilkinson MicrowaveAnisotropy Probe cosmic microwave background data

We introduce and analyze a method for testing statistical isotropy and Gaussianity andapply it to the Wilkinson Microwave Anisotropy Probe (WMAP) cosmic microwavebackground (CMB) foreground reduced temperature maps. We also test cross-channeldifference maps to constrain levels of residual foreground contamination and systematicuncertainties. We divide the sky into regions of varying size and shape and measure thefirst four moments of the one-point distribution within these regions, and using theirsimulated spatial distributions we test the statistical isotropy and Gaussianity hypotheses.By randomly varying orientations of these regions, we sample the underlying CMBfield in a new manner, that offers a richer exploration of the data content, andavoids possible biasing due to a single choice of sky division. In our analysis weaccount for all two-point correlations between different regions and also showthe impact on the results when these correlations are neglected. The statisticalsignificance is assessed via comparison with realistic Monte Carlo simulations.We find the three-year WMAP maps to agree well with the isotropic, Gaussian randomfield simulations as probed by regions corresponding to the angular scales ranging from6° to30° at68% confidence level (CL).We report a strong, anomalous(99.8% CL)dipole ‘excess’ in the V band of the three-year WMAP data and also in the V band of the WMAP five-yeardata (99.3% CL).Using our statistics, we notice large scale hemispherical power asymmetry, and find that itis not highly statistically significant in the WMAP three-year data () at scales . The significance is even smaller if multipoles up to are considered (∼90% CL). We give constraints on the amplitude of the previously proposed CMB dipolemodulation field parameter.We find some hints of foreground contamination in the form of a locally strong, anomalous kurtosis excessin the Q+V +W co-added map, which however is not significant globally.We easily detect the residual foregrounds in cross-band difference maps at rms level (at scales ) and limit the systematical uncertainties to (at scales ).

BAND-POWER RECONSTRUCTION OF PRIMORDIAL PERTURBATION SPECTRUM FROM CMB ANISOTROPY

The primordial curvature fluctuation spectrum is reconstructed in terms of the cosmic inversion method using the Wilkinson Microwave Anisotropy Probe data of the cosmic microwave background temperature anisotropy. Applying the covariance matrix analysis, the reconstructed spectrum is decomposed into statistically independent band powers. It is found that while statistically significant deviation from a simple power-law spectrum is found for first-year data, no such deviation is found for the three-year data except possibly at one point near the border of the wavenumber domain where accurate reconstruction is possible. This result, however, does not necessarily rule out theories predicting modulations in the power spectrum.

Fast optimal CMB power spectrum estimation with Hamiltonian sampling

We present a method for fast optimal estimation of the temperature angular power spectrum from observations of the cosmic microwave background. We employ a Hamiltonian Monte Carlo (HMC) sampler to obtain samples from the posterior probability distribution of all the power spectrum coefficients given a set of observations. We compare the properties of the HMC and the related Gibbs sampling approach on low-resolution simulations. The correlation lengths of the samples produced by Gibbs and HMC are generally comparable. At very high signal-to-noise (≳10) the Gibbs outperforms the HMC while for intermediate signal-to-noise (∼0.1–10) the HMC results in shorter correlation lengths than the Gibbs. At low signal-to-noise (≲0.1) both samplers appear to perform similarly. We also demonstrate the method on high-resolution data by applying it to simulated Wilkinson Microwave Anisotropy Probe (WMAP) data. Analysis of a single map from a WMAP-resolution data set is possible in around 80 h on a high-end desktop computer. HMC uses around a factor of 3–4 fewer spherical harmonic transforms than is reported for a Gibbs sampler (with pre-conditioning) and therefore produces noticeable performance gains. HMC imposes few conditions on the distribution to be sampled and obviates the requirement of having to be able to sample efficiently from the conditional densities, thus providing us with an extremely flexible approach upon which to build.

Testing cosmology with cosmic sound waves

Wilkinson Microwave Anisotropy Probe (WMAP) observations have accurately determined the position of the first two peaks and dips in the cosmic microwave background (CMB) temperature power spectrum. These encode information on the ratio of the distance to the last scattering surface to the sound horizon at decoupling. However prerecombination processes can contaminate this distance information. In order to assess the amplitude of these effects, we use the WMAP data and evaluate the relative differences of the CMB peak and dip multipoles. We find that the position of the first peak is largely displaced with respect to the expected position of the sound horizon scale at decoupling. In contrast, the relative spacings of the higher extrema are statistically consistent with those expected from perfect harmonic oscillations. This provides evidence for a scale dependent phase shift of the CMB oscillations which is caused by gravitational driving forces affecting the propagation of sound waves before recombination. By accounting for these effects we have performed a Markov Chain Monte Carlo likelihood analysis of the location of WMAP extrema to constrain, in combination with recent BAO data, a constant dark energy equation of state parameter $w$. For a flat universe we find a strong $2\ensuremath{\sigma}$ upper limit $wl\ensuremath{-}1.10$, and including the Hubble Space Telescope prior, we obtain $wl\ensuremath{-}1.14$, which is only marginally consistent with limits derived from the Supernova Legacy Survey sample. On the other hand, we infer larger limits for nonflat cosmologies. From the full CMB likelihood analysis, we also estimate the values of the shift parameter $R$ and the multipole ${l}_{a}$ of the acoustic horizon at decoupling for several cosmologies, to test their dependence on model assumptions. Although the analysis of the full CMB spectra should always be preferred, using the position of the CMB peaks and dips provides a simple and consistent method for combining CMB constraints with other data sets.

Testing primordial abundances with sterile neutrinos

The mixing between sterile and active neutrinos is taken into account in the calculation of Big Bang Nucleosynthesis. The abundances of primordial elements, like D, $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, and $^{7}\mathrm{Li}$, are calculated by including sterile neutrinos and by using finite chemical potentials. It is found that the resulting theoretical abundances are consistent with Wilkinson Microwave Anisotropy Probe (WMAP) data on baryonic densities, and with limits of Liquid Scintillator Neutrino Detector (LSND) on mixing angles, only if $^{7}\mathrm{Li}$ is excluded from the statistical analysis of theoretical and experimental results.

Brane inflation and the WMAP data: a Bayesian analysis

The Wilkinson Microwave Anisotropy Probe (WMAP) constraints on string inspired ‘braneinflation’ are investigated. Here, the inflaton field is interpreted as the distancebetween two branes placed in a flux-enriched background geometry and has aDirac–Born–Infeld (DBI) kinetic term. Our method relies on an exact numericalintegration of the inflationary power spectra coupled to a Markov chain Monte Carloexploration of the parameter space. This analysis is valid for any perturbativevalue of the string coupling constant and of the string length, and includes aphenomenological modelling of the reheating era to describe the post-inflationaryevolution. It is found that the data favour a scenario where inflation stops byviolation of the slow-roll conditions well before brane annihilation, rather than bytachyonic instability. As regards the background geometry, it is established thatlogv>−10 at95% confidence level(CL), where v is the dimensionless ratio of the five-dimensional sub-manifold at the baseof the six-dimensional warped conifold geometry to the volume of theunit 5-sphere. The reheating energy scale remains poorly constrained,Treh>20 GeV at95% CL, for an extreme equation of state () only. Assuming that the string length is known, the favoured values of the stringcoupling and of the Ramond–Ramond total background charge appear to be correlated.Finally, the stochastic regime (without and with volume effects) is studied using aperturbative treatment of the Langevin equation. The validity of such an approximatescheme is discussed and shown to be too limited for a full characterization of the quantumeffects.

A low cosmic microwave background variance in the Wilkinson Microwave Anisotropy Probe data

We have estimated the cosmic microwave background (CMB) variance from the three-year Wilkinson Microwave Anisotropy Probe (WMAP) data, finding a value which is significantly lower than the one expected from Gaussian simulations using the WMAP best-fitting cosmological model, at a significance level of 98.7 per cent. This result is even more prominent if we consider only the North ecliptic hemisphere (99.8 per cent). Different analyses have been performed in order to identify a possible origin for this anomaly. In particular, we have studied the behaviour of single-radiometer and single-year data as well as the effect of residual foregrounds and 1/f noise, finding that none of these possibilities can explain the low value of the variance. We have also tested the effect of varying the cosmological parameters, finding that the estimated CMB variance tends to favour higher values of n S than the one of the WMAP best-fitting model. In addition, we have also tested the consistency between the estimated CMB variance and the actual measured CMB power spectrum of the WMAP data, finding a strong discrepancy. A possible interpretation of this result could be a deviation from Gaussianity and/or isotropy of the CMB.

Detection of trans-Planckian effects in the cosmic microwave background

Quantum gravity effects are expected to modify the primordial density fluctuations produced during inflation and leave their imprint on the cosmic microwave background observed today. We present a new analysis discussing whether these effects are detectable, considering both currently available data and simulated results from an optimal CMB experiment. We find that the WMAP (Wilkinson Microwave Anisotropy Probe) data show no evidence for the particular signature considered in this work but give an upper bound on the parameters of the model. However, a hypothetical experiment shows that with proper data, the trans-Planckian effects should be detectable through alternate sampling methods. This fuzzy conclusion is a result of the nature of the oscillations, since they give rise to a likelihood hypersurface riddled with local maxima. A simple Bayesian analysis shows no significant evidence for the simulated data to prefer a trans-Planckian model. Conventional Markov chain Monte Carlo (MCMC) methods are not suitable for exploring this complicated landscape, but alternative methods are required to solve the problem. This, however, requires extremely high-precision data.

Constraining slow-roll inflation in the presence of dynamical dark energy

In this Letter we perform a global analysis of the constraints on the inflationary parameters in the presence of dynamical dark energy models from the current observations, including the three-year Wilkinson Microwave Anisotropy Probe (WMAP3) data, Boomerang-2K2, CBI, VSA, ACBAR, SDSS LRG, 2dFGRS and ESSENCE (192 sample). We use the analytic description of the inflationary power spectra in terms of the horizon-flow parameters {ϵi}. With the first order approximation in the slow-roll expansion, we find that the constraints on the horizon-flow parameters are ϵ1<0.014 (95% C.L.) and ϵ2=0.034±0.024 (1σ) in the ΛCDM model. In the framework of dynamical dark energy models, the constraints become obviously weak, ϵ1<0.022 (95% C.L.) and ϵ2=−0.006±0.039 (1σ), and the inflation models with a “blue” tilt, which are excluded about 2σ in the ΛCDM model, are allowed now. With the second order approximation, the constraints on the horizon-flow parameters are significantly relaxed further. If considering the non-zero ϵ3, the large running of the scalar spectral index is found for the ΛCDM model, as well as the dynamical dark energy models.

Searching for CPT Violation with Cosmic Microwave Background Data from WMAP and BOOMERANG

We search for signatures of Lorentz and $CPT$ violations in the cosmic microwave background (CMB) temperature and polarization anisotropies by using the Wilkinson Microwave Anisotropy Probe (WMAP) and the 2003 flight of BOOMERANG (B03) data. We note that if the Lorentz and $CPT$ symmetries are broken by a Chern-Simons term in the effective Lagrangian, which couples the dual electromagnetic field strength tensor to an external four-vector, the polarization vectors of propagating CMB photons will get rotated. Using the WMAP data alone, one could put an interesting constraint on the size of such a term. Combined with the B03 data, we found that a nonzero rotation angle of the photons is mildly favored: $\ensuremath{\Delta}\ensuremath{\alpha}=\ensuremath{-}6.0\genfrac{}{}{0}{}{+4.0}{\ensuremath{-}4.0}\genfrac{}{}{0}{}{+3.9}{\ensuremath{-}3.7}\text{ }\text{ }\mathrm{deg}(1,2\ensuremath{\sigma})$.

Anomalous SZ contribution to three-year WMAP data

We first show that the new Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr data confirm the detection by Myers et al. of an extended SZ signal centred on 606 Abell (ACO) clusters with richness class, R≥ 2. Our results also show SZ decrements around APM and 2MASS groups at increased significance than previously detected. We then follow the approach of Lieu, Mittaz & Zhang and compare the stacked WMAP results for the decrement in 31 clusters with ROSAT X-ray profiles where Lieu et al. found on average less SZ decrement in the WMAP 1-yr data than predicted. We confirm that in the 3-yr data these same clusters again show less SZ decrement than the X-ray data predict. We then analysed the WMAP results for the 38 X-ray clusters with OVRO/BIMA measured SZ decrements as presented by Bonamente et al.. We again find that the average decrement is measured to be significantly less (5.5σ) than predicted by the Chandra X-ray data. Thus while we confirm the original detection of an extended SZ effect by Myers et al., these X-ray comparisons may now suggest that the central SZ amplitudes detected by WMAP may actually be lower than expected. One possible explanation is that there is contamination of the WMAP SZ signal by radio sources in the clusters but we argue that this appears implausible. We then consider the possibility that the SZ decrement has been lensed away by foreground galaxy groups. Such a model predicts that the SZ decrement should depend on cluster redshift. A reduction in the SZ decrement with redshift is suggested from the ACO cluster sample and also from comparing the samples of Lieu et al. and Bonamente et al.. However, the mass power spectrum would require a far higher amplitude than currently expected if lensing was to explain the SZ deficit in high-redshift clusters.

Squark decays in MSSM under the cosmological bounds

We present the numerical investigation of the fermionic two-body decays of squarks in the minimal supersymmetric standard model with complex parameters. In the analysis, we particularly take into account the cosmological bounds imposed by Wilkinson Microwave Anisotropy Probe data. We find that the phase dependences of the decay widths of the third family squarks, as well as those of the first and second families, are quite significant which can provide viable probes of additional CP sources. We plot the CP-phase dependences for each fermionic two-body decay channel of squarks (i = 1, 2, q = u, d, c, s, t, b) and speculate about the branching ratios and total (two-body) decay widths.

Current constraints on interacting holographic dark energy

Although there is mounting observational evidence that the cosmic expansion is undergoing a late-time acceleration, the physical mechanism behind such a phenomenon is yet unknown. In this Letter, we investigate a holographic dark energy (HDE) model with interaction between the components of the dark sector in the light of current cosmological observations. We use both the new gold sample of 182 type Ia supernovae (SNe Ia) and the 192 SNe Ia ESSENCE data, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and the shift parameter from the three-year Wilkinson Microwave Anisotropy Probe data. In agreement with previous results, we show that these observations suggest a very weak coupling or even a noninteracting HDE. The phantom crossing behavior in the context of these scenarios is also briefly discussed.