Induced CMB quadrupole from pointing offsets

Recent claims in the literature have suggested that the {\it WMAP} quadrupole is not primordial in origin, and arises from an aliasing of the much larger dipole field because of incorrect satellite pointing. We attempt to reproduce this result and delineate the key physics leading to the effect. We find that, even if real, the induced quadrupole would be smaller than claimed. We discuss reasons why the {\it WMAP} data are unlikely to suffer from this particular systematic effect, including the implications for observations of point sources. Given this evidence against the reality of the effect, the similarity between the pointing-offset-induced signal and the actual quadrupole then appears to be quite puzzling. However, we find that the effect arises from a convolution between the gradient of the dipole field and anisotropic coverage of the scan direction at each pixel. There is something of a directional conspiracy here -- the dipole signal lies close to the Ecliptic Plane, and its direction, together with the {\it WMAP} scan strategy, results in a strong coupling to the $Y_{2,\,-1}$ component in Ecliptic co-ordinates. The dominant strength of this component in the measured quadrupole suggests that one should exercise increased caution in interpreting its estimated amplitude. The {\it Planck} satellite has a different scan strategy which does not so directly couple the dipole and quadrupole in this way and will soon provide an independent measurement.Comment: 8 pages, 4 figure

Tensors, non-Gaussianities, and the future of potential reconstruction

We present projections for reconstruction of the inflationary potential expected from ESA's upcoming Planck Surveyor CMB mission. We focus on the effects that tensor perturbations and the presence of non-Gaussianities have on reconstruction efforts in the context of non-canonical inflation models. We consider potential constraints for different combinations of detection/null-detection of tensors and non-Gaussianities. We perform Markov Chain Monte Carlo and flow analyses on a simulated Planck-precision data set to obtain constraints. We find that a failure to detect non-Gaussianities precludes a successful inversion of the primordial power spectrum, greatly affecting uncertainties, even in the presence of a tensor detection. In the absence of a tensor detection, while unable to determine the energy scale of inflation, an observable level of non-Gaussianities provides correlations between the errors of the potential parameters, suggesting that constraints might be improved for suitable combinations of parameters. Constraints are optimized for a positive detection of both tensors and non-Gaussianities.Comment: 12 pages, 5 figures, LaTeX; V2: version submitted to JCA

Cosmological CPT Violation and CMB Polarization Measurements

In this paper we study the possibility of testing Charge-Parity-Time Reversal (CPT) symmetry with cosmic microwave background (CMB) experiments. We consider two kinds of Chern-Simons (CS) term, electromagnetic CS term and gravitational CS term, and study their effects on the CMB polarization power spectra in detail. By combining current CMB polarization measurements, the seven-year WMAP, BOOMERanG 2003 and BICEP observations, we obtain a tight constraint on the rotation angle $\Delta\alpha=-2.28\pm1.02$ deg ($1\,\sigma$), indicating a $2.2\,\sigma$ detection of the CPT violation. Here, we particularly take the systematic errors of CMB measurements into account. After adding the QUaD polarization data, the constraint becomes $-1.34<\Delta\alpha<0.82$ deg at 95% confidence level. When comparing with the effect of electromagnetic CS term, the gravitational CS term could only generate TB and EB power spectra with much smaller amplitude. Therefore, the induced parameter $\epsilon$ can not be constrained from the current polarization data. Furthermore, we study the capabilities of future CMB measurements, Planck and CMBPol, on the constraints of $\Delta\alpha$ and $\epsilon$. We find that the constraint of $\Delta\alpha$ can be significantly improved by a factor of 15. Therefore, if this rotation angle effect can not be taken into account properly, the constraints of cosmological parameters will be biased obviously. For the gravitational CS term, the future Planck data still can not constrain $\epsilon$ very well, if the primordial tensor perturbations are small, $r <0.1$. We need the more accurate CMBPol experiment to give better constraint on $\epsilon$.Comment: 11 pages, 5 figures, 4 tables, Accepted for publication in JCA

The High Redshift Integrated Sachs-Wolfe Effect

In this paper we rely on the quasar (QSO) catalog of the Sloan Digital Sky Survey Data Release Six (SDSS DR6) of about one million photometrically selected QSOs to compute the Integrated Sachs-Wolfe (ISW) effect at high redshift, aiming at constraining the behavior of the expansion rate and thus the behaviour of dark energy at those epochs. This unique sample significantly extends previous catalogs to higher redshifts while retaining high efficiency in the selection algorithm. We compute the auto-correlation function (ACF) of QSO number density from which we extract the bias and the stellar contamination. We then calculate the cross-correlation function (CCF) between QSO number density and Cosmic Microwave Background (CMB) temperature fluctuations in different subsamples: at high z>1.5 and low z<1.5 redshifts and for two different choices of QSO in a conservative and in a more speculative analysis. We find an overall evidence for a cross-correlation different from zero at the 2.7\sigma level, while this evidence drops to 1.5\sigma at z>1.5. We focus on the capabilities of the ISW to constrain the behaviour of the dark energy component at high redshift both in the \LambdaCDM and Early Dark Energy cosmologies, when the dark energy is substantially unconstrained by observations. At present, the inclusion of the ISW data results in a poor improvement compared to the obtained constraints from other cosmological datasets. We study the capabilities of future high-redshift QSO survey and find that the ISW signal can improve the constraints on the most important cosmological parameters derived from Planck CMB data, including the high redshift dark energy abundance, by a factor \sim 1.5.Comment: 20 pages, 18 figures, and 7 table

Early Dark Energy at High Redshifts: Status and Perspectives

Early dark energy models, for which the contribution to the dark energy density at high redshifts is not negligible, influence the growth of cosmic structures and could leave observable signatures that are different from the standard cosmological constant cold dark matter ($\Lambda$CDM) model. In this paper, we present updated constraints on early dark energy using geometrical and dynamical probes. From WMAP five-year data, baryon acoustic oscillations and type Ia supernovae luminosity distances, we obtain an upper limit of the dark energy density at the last scattering surface (lss), $\Omega_{\rm EDE}(z_{\rm lss})<2.3\times10^{-2}$ (95% C.L.). When we include higher redshift observational probes, such as measurements of the linear growth factors, Gamma-Ray Bursts (GRBs) and Lyman-$\alpha$ forest (\lya), this limit improves significantly and becomes $\Omega_{\rm EDE}(z_{\rm lss})<1.4\times10^{-3}$ (95% C.L.). Furthermore, we find that future measurements, based on the Alcock-Paczy\'nski test using the 21cm neutral hydrogen line, on GRBs and on the \lya forest, could constrain the behavior of the dark energy component and distinguish at a high confidence level between early dark energy models and pure $\Lambda$CDM. In this case, the constraints on the amount of early dark energy at the last scattering surface improve by a factor ten, when compared to present constraints. We also discuss the impact on the parameter $\gamma$, the growth rate index, which describes the growth of structures in standard and in modified gravity models.Comment: 11 pages, 9 figures and 4 table

The dark side of curvature

Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d_A(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Omega_k in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d_A(z) up to sufficiently high redshifts around z = 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z)-Omega_k degeneracy.Comment: 18 pages, 9 figures. Minor changes, matches version accepted in JCA

Constraints on cosmic hemispherical power anomalies from quasars

Recent analyses of the cosmic microwave background (CMB) maps from the WMAP satellite have uncovered evidence for a hemispherical power anomaly, i.e. a dipole modulation of the CMB power spectrum at large angular scales with an amplitude of +/-14 percent. Erickcek et al have put forward an inflationary model to explain this anomaly. Their scenario is a variation on the curvaton scenario in which the curvaton possesses a large-scale spatial gradient that modulates the amplitude of CMB fluctuations. We show that this scenario would also lead to a spatial gradient in the amplitude of perturbations sigma_8, and hence to a dipole asymmetry in any highly biased tracer of the underlying density field. Using the high-redshift quasars from the Sloan Digital Sky Survey, we find an upper limit on such a gradient of |nabla sigma_8|/sigma_8<0.027/r_{lss} (99% posterior probability), where r_{lss} is the comoving distance to the last-scattering surface. This rules out the simplest version of the curvaton spatial gradient scenario.Comment: matches JCAP accepted version (minor revisions

Constraints from CMB in the intermediate Brans-Dicke inflation

We study an intermediate inflationary stage in a Jordan-Brans-Dicke theory. In this scenario we analyze the quantum fluctuations corresponding to adiabatic and isocurvature modes. Our model is compared to that described by using the intermediate model in Einstein general relativity theory. We assess the status of this model in light of the seven-year WMAP data.Comment: 17 pages, 6 figure

Anthropically Selected Baryon Number and Isocurvature Constraints

The similarity of the observed baryon and dark matter densities suggests that they are physically related, either via a particle physics mechanism or anthropic selection. A pre-requisite for anthropic selection is the generation of superhorizon-sized domains of different Omega_{B}/Omega_{DM}. Here we consider generation of domains of different baryon density via random variations of the phase or magnitude of a complex field Phi during inflation. Baryon isocurvature perturbations are a natural consequence of any such mechanism. We derive baryon isocurvature bounds on the expansion rate during inflation H_{I} and on the mass parameter mu which breaks the global U(1) symmetry of the Phi potential. We show that when mu < H_{I} (as expected in SUSY models) the baryon isocurvature constraints can be satisfied only if H_{I} is unusually small, H_{I} < 10^{7} GeV, or if non-renormalizable Planck-suppressed corrections to the Phi potential are excluded to a high order. Alternatively, an unsuppressed Phi potential is possible if mu is sufficiently large, mu > 10^{16} GeV. We show that the baryon isocurvature constraints can be naturally satisfied in Affleck-Dine baryogenesis, as a result of the high-order suppression of non-renormalizable terms along MSSM flat directions.Comment: 8 pages, 1 eps figure, LaTeX. Minor typo correcte

Constraints on the SZ Power Spectrum on Degree Angular Scales in WMAP Data

The Sunyaev-Zel'dovich (SZ) effect has a distinct spectral signature that allows its separation from fluctuations in the cosmic microwave background (CMB) and foregrounds. Using CMB anisotropies measured in Wilkinson Microwave Anisotropy Probe's five-year maps, we constrain the SZ fluctuations at large, degree angular scales corresponding to multipoles in the range from 10 to 400. We provide upper bounds on SZ fluctuations at multipoles greater than 50, and find evidence for a hemispherically asymmetric signal at ten degrees angular scales. The amplitude of the detected signal cannot be easily explained with the allowed number density and temperature of electrons in the Galactic halo. We have failed to explain the excess signal as a residual from known Galactic foregrounds or instrumental uncertainties such as 1/f-noise.Comment: 14 pages, 3 figures, 2 tables. Simple typos fixe