The integrated Sachs-Wolfe imprint of cosmic superstructures: a problem for ΛCDM

Journal of Cosmology and Astroparticle Physics (Impact Factor: 5.88). 06/2012; 2012(06):042-042. DOI: 10.1088/1475-7516/2012/06/042
Source: arXiv

ABSTRACT A crucial diagnostic of the ΛCDM cosmological model is the integrated Sachs-Wolfe (ISW) effect of large-scale structure on the cosmic microwave background (CMB). The ISW imprint of superstructures of size ∼ 100 h−1Mpc at redshift z ∼ 0.5 has been detected with > 4σ significance, however it has been noted that the signal is much larger than expected. We revisit the calculation using linear theory predictions in ΛCDM cosmology for the number density of superstructures and their radial density profile, and take possible selection effects into account. While our expected signal is larger than previous estimates, it is still inconsistent by > 3σ with the observation. If the observed signal is indeed due to the ISW effect then huge, extremely underdense voids are far more common in the observed universe than predicted by ΛCDM.


Available from: Subir Sarkar, Feb 28, 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The accelerating expansion of the universe at recent epochs is encoded in the cosmic microwave background: a few percent of the total temperature fluctuations are generated by evolving gravitational potentials which trace the large-scale structures in the universe. This signature of dark energy, the Integrated Sachs-Wolfe Effect, has been detected by averaging temperatures in the WMAP sky maps corresponding to the directions of superstructures in the Sloan Digital Sky Survey data release 6. We model the maximum average peak signal expected in the standard $\Lambda$CDM cosmological model, using Gaussian random realizations of the microwave sky, including correlations between different physical contributions to the temperature fluctuations and between different redshift ranges of the evolving gravitational potentials. We find good agreement with the mean temperature peak amplitude from previous theoretical estimates based on large-scale structure simulations, but with larger statistical uncertainties. We apply our simulation pipeline to four different foreground-cleaned microwave temperature maps from Planck and WMAP data, finding a mean temperature peak signal at previously identified sky locations which exceeds our theoretical mean signal at a statistical significance of about $2.5\sigma$ and which differs from a null signal at $3.5\sigma$.
    Physical Review D 10/2014; 91(4). DOI:10.1103/PhysRevD.91.043510 · 4.86 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We construct a viable cosmological model based on velocity diffusion of matter particles. In order to ensure the conservation of the total energy-momentum tensor in the presence of diffusion, we include a cosmological scalar field $\phi$ which we identify with the dark energy component of the Universe. The model is characterized by only one new degree of freedom, the diffusion parameter $\sigma$. The standard $\Lambda$CDM model can be recovered by setting $\sigma=0$. If diffusion takes place ($\sigma >0$) the dynamics of the matter and of the dark energy fields are coupled. We argue that the existence of a diffusion mechanism in the Universe can serve as a theoretical motivation for interacting models. We constrain the background dynamics of the diffusion model with Supernovae, H(z) and BAO data. We also perform a perturbative analysis of this model in order to understand structure formation in the Universe. We calculate the impact of diffusion both on the CMB spectrum, with particular attention to the integrated Sachs-Wolfe signal, and on the matter power spectrum $P(k)$. The latter analysis places strong constraints on the magnitude of the diffusion mechanism but does not rule out the model.
    Journal of Cosmology and Astroparticle Physics 08/2013; DOI:10.1088/1475-7516/2013/11/025 · 5.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Detailed knowledge of the primordial power spectrum (PPS) of curvature perturbations is essential both in order to elucidate the physical mechanism (`inflation') which generated it, and for estimating the parameters of the assumed cosmological model from CMB and LSS data. Hence it ought to be extracted from such data in a model-independent manner, however this is difficult because relevant cosmological observables are given in general by a convolution of the PPS with some smoothing kernel. The deconvolution problem is ill-conditioned so a regularisation scheme must be employed to control error propagation. We demonstrate that `Tikhonov regularisation' can robustly reconstruct the PPS from multiple cosmological data sets, a significant advantage being that both its uncertainty and resolution are precisely quantified. Using Monte Carlo simulations we investigate the performance of several regularisation parameter selection methods and find that generalised cross-validation and Mallow's C_p method give optimal results. We apply our inversion procedure to data from the Wilkinson Microwave Anisotropy Probe, other ground-based small angular scale CMB experiments, and the Sloan Digital Sky Survey. The reconstructed PPS is not scale-free but has an infrared cutoff at k <= 5 X 10^{-4} Mpc^{-1} (due to the low CMB quadrupole) and several features with ~2 sigma significance at k/Mpc^{-1} = 0.0013-0.0023, 0.0362-0.0402 and 0.051-0.056, reflecting the WMAP `glitches'. To test whether these are indeed real will require more accurate data, such as from the Planck satellite and new ground-based experiments.
    Journal of Cosmology and Astroparticle Physics 08/2013; 2014(01). DOI:10.1088/1475-7516/2014/01/025 · 5.88 Impact Factor