Cosmic Microwave Anisotropy Research Articles

Interacting dark energy in a closed universe

ABSTRACT Recent measurements of the Cosmic Microwave Anisotropies power spectra measured by the Planck satellite show a preference for a closed universe at more than $99 {{\ \rm per\ cent}}$ confidence level (CL). Such a scenario is however in disagreement with several low redshift observables, including luminosity distances of Type Ia supernovae. Here we show that interacting dark energy (IDE) models can ease the discrepancies between Planck and supernovae Ia data in a closed Universe, leading to a preference for both a coupling and a curvature different from zero above the 99 per cent CL. Therefore IDE cosmologies remain as very appealing scenarios, as they can provide the solution to a number of observational tensions in different fiducial cosmologies. The results presented here strongly favour broader analyses of cosmological data, and suggest that relaxing the usual flatness and vacuum energy assumptions can lead to a much better agreement among theory and observations.

Lensing and the Warm-hot Intergalactic Medium

Abstract The correlation of weak lensing and Cosmic Microwave Anisotropy (CMB) data traces the pressure distribution of the hot, ionized gas and the underlying matter density field. The measured correlation is dominated by baryons residing in halos. Detecting the contribution from unbound gas by measuring the residual cross-correlation after masking all known halos requires a theoretical understanding of this correlation and its dependence with model parameters. Our model assumes that the gas in filaments is well described by a log-normal probability distribution function, with temperatures 105–7 K and overdensities ξ ≤ 100. The lensing-Comptonization cross-correlation is dominated by gas with overdensities in the range ξ ≈ [3–33]; the signal is generated at redshifts z ≤ 1. If only 10% of the measured cross-correlation is due to unbound gas, then the most recent measurements set an upper limit of on the mean temperature of the intergalactic Medium. The amplitude is proportional to the baryon fraction stored in filaments. The lensing-Comptonization power spectrum peaks at a different scale than the gas in halos, making it possible to distinguish both contributions. To trace the distribution of the low-density and low-temperature plasma on cosmological scales, the effect of halos will have to be subtracted from the data, requiring observations with larger signal-to-noise ratios than are currently available.

Constraining dark energy dynamics in extended parameter space

Dynamical dark energy has been recently suggested as a promising and physical way to solve the 3.4 sigma tension on the value of the Hubble constant $H_0$ between the direct measurement of Riess et al. (2016) (R16, hereafter) and the indirect constraint from Cosmic Microwave Anisotropies obtained by the Planck satellite under the assumption of a $\Lambda$CDM model. In this paper, by parameterizing dark energy evolution using the $w_0$-$w_a$ approach, and considering a $12$ parameter extended scenario, we find that: a) the tension on the Hubble constant can indeed be solved with dynamical dark energy, b) a cosmological constant is ruled out at more than $95 \%$ c.l. by the Planck+R16 dataset, and c) all of the standard quintessence and half of the "downward going" dark energy model space (characterized by an equation of state that decreases with time) is also excluded at more than $95 \%$ c.l. These results are further confirmed when cosmic shear, CMB lensing, or SN~Ia luminosity distance data are also included. However, tension remains with the BAO dataset. A cosmological constant and small portion of the freezing quintessence models are still in agreement with the Planck+R16+BAO dataset at between 68\% and 95\% c.l. Conversely, for Planck plus a phenomenological $H_0$ prior, both thawing and freezing quintessence models prefer a Hubble constant of less than 70 km/s/Mpc. The general conclusions hold also when considering models with non-zero spatial curvature.

Evolution of clusters and cosmology

Recent Sunyaev–Zeldovich (SZ) surveys (ACT, Planck, SPT) have provided new cluster catalogs, very significantly expanding the coverage of the mass–redshift plane, while XMM‐Newton surveys are pushing cluster detection to lower masses, up to z ∼ 1 and beyond. Cosmological analysis of the new cluster samples, particularly that of the largest Planck sample, found fewer clusters than predicted by the base Planck ΛCDM model derived from cosmic microwave (CMB) anisotropies. This could imply a need for extension of the model and/or a revision of cluster physics. In parallel, Chandra and XMM‐Newton follow‐up programs on these new SZ‐discovered clusters have improved our knowledge of evolution, as well as providing new information on survey selection. These results challenge our understanding of fundamental issues such as (a) what the true mass of clusters is, with implications for the baryon depletion at cluster scales and cluster dynamical evolution, and (b) what the true underlying population is, that we are only partly detecting at various wavelengths. Potential new observations to address these issues with XMM‐Newton in conjunction with other observatories are discussed.

Power spectrum of flow fluctuations in relativistic heavy-ion collisions

We carry out hydrodynamical simulation of the evolution of fluid in relativistic heavy-ion collisions with random initial fluctuations. The time evolution of power spectrum of momentum anisotropies shows very strong correspondence with the physics of cosmic microwave anisotropies as was earlier predicted by us. In particular, our results demonstrate suppression of superhorizon fluctuations and the correspondence between the location of the first peak in the power spectrum of momentum anisotropies and the length scale of fluctuations and expected freeze-out time-scale (more precisely, the sound horizon size at freeze-out).

Constraining topological defects with temperature and polarization anisotropies

We analyze the possible contribution of topological defects to cosmic microwave anisotropies, both temperature and polarization. We allow for the presence of both inflationary scalars and tensors, and of polarized dust foregrounds that may contribute to or dominate the B-mode polarization signal. We confirm and quantify our previous statements that topological defects on their own are a poor fit to the B-mode signal. However, adding topological defects to a model with a tensor component or a dust component improves the fit around $\ensuremath{\ell}=200$. Fitting simultaneously to both temperature and polarization data, we find that textures fit almost as well as tensors ($\mathrm{\ensuremath{\Delta}}{\ensuremath{\chi}}^{2}=2.0$), while Abelian Higgs strings are ruled out as the sole source of the B-mode signal at low $\ensuremath{\ell}$. The 95% confidence upper limits on models combining defects and dust are $G\ensuremath{\mu}<2.7\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}7}$ (Abelian Higgs strings), $G\ensuremath{\mu}<9.8\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}7}$ (semilocal strings) and $G\ensuremath{\mu}<7.3\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}7}$ (textures), a small reduction on the Planck bounds. The most economical fit overall is obtained by the standard $\mathrm{\ensuremath{\Lambda}}$--cold dark matter model with a polarized dust component.

CLUSTERING OF SLOAN DIGITAL SKY SURVEY III PHOTOMETRIC LUMINOUS GALAXIES: THE MEASUREMENT, SYSTEMATICS, AND COSMOLOGICAL IMPLICATIONS

The Sloan Digital Sky Survey (SDSS) surveyed 14,555 square degrees, and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between $z=0.45$ and $z=0.65$, constructed from the SDSS using methods described in Ross et al. (2011). This data-set spans 11,000 square degrees and probes a volume of $3h^{-3} \rm{Gpc}^3$, making it the largest volume ever used for galaxy clustering measurements. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at 4 redshift slices with an accuracy of ~15% with bin size of delta_l = 10 on scales of the Baryon Acoustic Oscillations (BAO) (at l~40-400). We derive cosmological constraints using the full-shape of the power-spectra. For a flat Lambda CDM model, when combined with Cosmic Microwave Background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H_0 constraints from 600 Cepheids observed by HST, we find \Omega_\Lambda = 0.73 +/- 0.019 and H_0 to be 70.5 +/- 1.6 km/s/Mpc. For an open Lambda CDM model, when combined with WMAP7 + HST, we find $\Omega_K = 0.0035 +/- 0.0054, improved over WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we find w = -1.071 +/- 0.078, and H_0 to be 71.3 +/- 1.7 km/s/Mpc, which is competitive with the latest large scale structure constraints from large spectroscopic surveys such as SDSS Data Release 7 (DR7) (Reid et al. 2010, Percival et al. 2010, Montesano et al. 2011) and WiggleZ (Blake et al. 2011). The SDSS-III Data Release 8 (SDSS-III DR8) Angular Clustering Data allows a wide range of investigations into the cosmological model, cosmic expansion (via BAO), Gaussianity of initial conditions and neutrino masses. (abridged)

Axion Dark Matter and Cosmological Parameters

We observe that photon cooling after big bang nucleosynthesis but before recombination can remove the conflict between the observed and theoretically predicted value of the primordial abundance of ^{7}Li. Such cooling is ordinarily difficult to achieve. However, the recent realization that dark matter axions form a Bose-Einstein condensate provides a possible mechanism because the much colder axions may reach thermal contact with the photons. This proposal predicts a high effective number of neutrinos as measured by the cosmic microwave anisotropy spectrum.

Tilted physics: A cosmologically dipole-modulated sky

Physical constants and cosmological parameters could vary with position. On the largest scales such variations would manifest themselves as gradients across our Hubble volume, leading to dipole-modulation of the cosmic microwave anisotropies. This generically leads to a correlation between adjacent multipoles in the spherical harmonics expansion of the sky, a distinctive signal which should be searched for in future data sets.

CMB in a box: Causal structure and the Fourier-Bessel expansion

This paper makes two points. First, we show that the line-of-sight solution to cosmic microwave anisotropies in Fourier space, even though formally defined for arbitrarily large wavelengths, leads to position-space solutions which only depend on the sources of anisotropies inside the past light-cone of the observer. This happens order by order in a series expansion in powers of the visibility $\gamma=e^{-\mu}$, where $\mu$ is the optical depth to Thompson scattering. We show that the CMB anisotropies are regulated by spacetime window functions which have support only inside the past light-cone of the point of observation. Second, we show that the Fourier-Bessel expansion of the physical fields (including the temperature and polarization momenta) is an alternative to the usual Fourier basis as a framework to compute the anisotropies. In that expansion, for each multipole $l$ there is a discrete tower of momenta $k_{i,l}$ (not a continuum) which can affect physical observables, with the smallest momenta being $k_{1,l} ~ l$. The Fourier-Bessel modes take into account precisely the information from the sources of anisotropies that propagates from the initial value surface to the point of observation - no more, no less. We also show that the physical observables (the temperature and polarization maps), and hence the angular power spectra, are unaffected by that choice of basis. This implies that the Fourier-Bessel expansion is the optimal scheme with which one can compute CMB anisotropies. (Abridged)

Manifestly gauge-invariant general relativistic perturbation theory: I. Foundations

Linear cosmological perturbation theory is pivotal to a theoretical understanding of current cosmological experimental data provided e.g. by cosmic microwave anisotropy probes. A key issue in that theory is to extract the gauge-invariant degrees of freedom which allow unambiguous comparison between theory and experiment. When one goes beyond first (linear) order, the task of writing the Einstein equations expanded to nth order in terms of quantities that are gauge-invariant up to terms of higher orders becomes highly non-trivial and cumbersome. This fact has prevented progress for instance on the issue of the stability of linear perturbation theory and is a subject of current debate in the literature. In this series of papers we circumvent these difficulties by passing to a manifestly gauge-invariant framework. In other words, we only perturb gauge-invariant, i.e. measurable quantities, rather than gauge variant ones. Thus, gauge invariance is preserved non-perturbatively while we construct the perturbation theory for the equations of motion for the gauge-invariant observables to all orders. In this first paper we develop the general framework which is based on a seminal paper due to Brown and Kuchař as well as the relational formalism due to Rovelli. In the second, companion, paper we apply our general theory to FRW cosmologies and derive the deviations from the standard treatment in linear order. As it turns out, these deviations are negligible in the late universe, thus our theory is in agreement with the standard treatment. However, the real strength of our formalism is that it admits a straightforward and unambiguous, gauge-invariant generalization to higher orders. This will also allow us to settle the stability issue in a future publication.

CANNY ALGORITHM, COSMIC STRINGS AND THE COSMIC MICROWAVE BACKGROUND

We describe a new code to search for signatures of cosmic strings in cosmic microwave anisotropy maps. The code implements the Canny algorithm, an edge detection algorithm designed to search for the lines of large gradients in maps. Such a gradient signature which is coherent in position-space is produced by cosmic strings via the Kaiser–Stebbins effect. We test the power of our new code to set limits on the tension of the cosmic strings by analyzing simulated data, with and without cosmic strings. We compare maps with a pure Gaussian scale-invariant power spectrum with maps which have a contribution of a distribution of cosmic strings obeying a scaling solution. The maps have angular scale and angular resolution comparable to what current and future ground-based small-scale cosmic microwave anisotropy experiments will achieve. We present tests of the codes, indicate the limits on the string tension which could be set with the current code, and describe various ways to refine the analysis. Our results indicate that when applied to the data of ongoing cosmic microwave experiments such as the South Pole Telescope project, the sensitivity of our method to the presence of cosmic strings will be more than an order of magnitude better than the limits from existing analyses.

DARK MATTER AXIONS

The hypothesis of an 'invisible' axion was made by Misha Shifman and others, approximately thirty years ago. It has turned out to be an unusually fruitful idea, crossing boundaries between particle physics, astrophysics and cosmology. An axion with mass of order 10-5 eV (with large uncertainties) is one of the leading candidates for the dark matter of the universe. It was found recently that dark matter axions thermalize and form a Bose-Einstein condensate (BEC). Because they form a BEC, axions differ from ordinary cold dark matter (CDM) in the non-linear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles. Because there is evidence for these phenomena, unexplained with ordinary CDM, an argument can be made that the dark matter is axions.

Bose-Einstein Condensation of Dark Matter Axions

We show that cold dark matter axions thermalize and form a Bose-Einstein condensate (BEC). We obtain the axion state in a homogeneous and isotropic universe, and derive the equations governing small axion perturbations. Because they form a BEC, axions differ from ordinary cold dark matter in the nonlinear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles.

Bayesian Limits on Primordial Isotropy Breaking

It is often assumed that primordial perturbations are statistically isotropic, which implies, among other properties, that their power spectrum is invariant under rotations. In this article, we test this assumption by placing bounds on deviations from rotational invariance of the primordial spectrum. Using five-year Wilkinson Microwave Anisotropy Probe cosmic microwave anisotropy maps, we set limits on the overall norm and the amplitude of individual components of the primordial spectrum quadrupole and hexadecapole. We find that there is no significant evidence for primordial isotropy breaking, and constrain the relative contribution of the quadrupole and hexadecapole to be less than, respectively, 23% and 34% at 95% confidence level.

Planckand re-ionization history: a model selection view

We use Bayesian model selection tools to forecast the Planck satellite's ability to distinguish between different models for the re-ionization history of the Universe, using the large angular scale signal in the cosmic microwave background polarization spectrum. We find that Planck is not expected to be able to distinguish between an instantaneous re-ionization model and a two-parameter smooth re-ionization model, except for extreme values of the additional re-ionization parameter. If it cannot, then it will be unable to distinguish between different two-parameter models either. However, Bayesian model averaging will be needed to obtain unbiased estimates of the optical depth to re-ionization. We also generalize our results to a hypothetical future cosmic variance limited microwave anisotropy survey, where the outlook is more optimistic.

Cosmic microwave weak lensing data as a test for the dark universe

Combined analyses of WMAP 3-year and ACBAR cosmic microwave anisotropies angular power spectra have presented evidence for gravitational lensing at $g3\ensuremath{\sigma}$ level. This signal could provide a relevant test for cosmology. After evaluating and confirming the statistical significance of the detection in light of the new WMAP 5-year data, we constrain a new parameter ${A}_{L}$ that scales the lensing potential such that ${A}_{L}=0$ corresponds to unlensed while ${A}_{L}=1$ is the expected lensed result in the standard $\ensuremath{\Lambda}\mathrm{\text{\ensuremath{-}}}\mathrm{CDM}$ model. We find from $\mathrm{WMAP}5+\mathrm{ACBAR}$ a $2.5\ensuremath{\sigma}$ indication for a lensing contribution larger than expected, with ${A}_{L}={3.1}_{\ensuremath{-}1.5}^{+1.8}$ at 95% C.L. The result is stable under the assumption of different templates for an additional Sunyaev-Zel'dovich foreground component or the inclusion of an extra background of cosmic strings. We find negligible correlation with other cosmological parameters as, for example, the energy density in massive neutrinos. While unknown systematics may be present, dark energy or modified gravity models could be responsible for the over-smoothness of the power spectrum. Near-future data, most notably from the Planck satellite mission, will scrutinize this interesting possibility.

Inflation and WMAP three year data: Features are still present

The new 3 year WMAP data seem to confirm the presence of nonstandard large scale features in the cosmic microwave anisotropy power spectrum. While these features may hint at uncorrected experimental systematics, it is also possible to generate, in a cosmological way, oscillations on large angular scales by introducing a sharp step in the inflaton potential. Using current cosmological data, we derive constraints on the position, magnitude and gradient of a possible step. We show that a step in the inflaton potential, while strongly constrained by current data, is still allowed and may provide an interesting explanation to the currently measured deviations from the standard featureless spectrum. Moreover, we show that inflationary oscillations in the primordial power spectrum can significantly bias parameter estimates from standard ruler methods involving measurements of baryon oscillations.

Flipped [formula omitted] predicts [formula omitted

We discuss hybrid inflation in supersymmetric flipped SU(5) model such that the cosmic microwave anisotropy δT/T is essentially proportional to (M/MP)2, where M denotes the symmetry breaking scale and MP (=2.4×1018 GeV) is the reduced Planck mass. The magnitude of M determined from δT/T measurements can be consistent with the value inferred from the evolution of SU(3) and SU(2) gauge couplings. In other words, one could state that flipped SU(5) predicts (more precisely ‘postdicts’) δT/T. The scalar spectral index ns=0.993±0.007, the scalar to tensor ratio satisfies r≲10−6, while dns/dlnk≲4×10−4.

Test of modified Newtonian dynamics with recent Boomerang data

Purely baryonic dark matter dominated models like modified Newtonian dynamics (MOND) based on modification of Newtonian gravity have been successful in reproducing some dynamical properties of galaxies. More recently, a relativistic formulation of MOND proposed by Bekenstein seems to agree with cosmological large scale structure formation. In this work, we revise the agreement of MOND with observations in light of the new results on the cosmic microwave anisotropies provided by the 2003 flight of Boomerang. The measurements of the height of the third acoustic peak, provided by several small scale CMB experiments have reached enough sensitivity to severely constrain models without cold dark matter. Assuming that acoustic peak structure in the CMB is unchanged and that local measurements of the Hubble constant can be applied, we find that the cold dark matter is strongly favored with Bayesian probability ratio of about one in two hundred.