‘The Integrated Sachs-Wolfe Imprints of Cosmic Superstructures: A Problem for cdm’

Journal of Cosmology and Astroparticle Physics (Impact Factor: 5.81). 06/2012; 2012(06):042-042. DOI: 10.1088/1475-7516/2012/06/042
Source: arXiv


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.

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Available from: Subir Sarkar, Feb 28, 2014
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    • "We use the same parameter values as in ref. [28], which are the mean values obtained from a fit to WMAP 7-year [36] and SDSS DR7 data [37]. However, the precise choice is unimportant, since variation of parameter values within the ranges allowed by the concordance cosmology has a negligible effect on the spherical model prediction [28]. To calculate the matter power spectrum P (k) at the requisite redshift we use CAMB [38]. "
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    ABSTRACT: A detection of the stacked integrated Sachs-Wolfe (ISW) signal in the CMB of rare superstructures identified in the SDSS Luminous Red Galaxy catalogue has been reported at very high statistical significance. The magnitude of the observed signal has previously been argued to be more than 3 standard deviations larger than the theoretical \Lambda CDM expectation. However, this calculation was made in the linear approximation, and relied on assumptions that may potentially have caused the \Lambda CDM expectation to be underestimated. Here we update the theoretical model calculation and compare it with an analysis of ISW maps obtained from N-body simulations of a \Lambda CDM universe. The differences between model predictions and the map analyses are found to be small and cannot explain the discrepancy with observation, which remains at >3 s.d. significance. We discuss the cosmological significance of this anomaly and speculate on the potential of alternative models to explain it.
    Journal of Cosmology and Astroparticle Physics 12/2012; 2013(02). DOI:10.1088/1475-7516/2013/02/013 · 5.81 Impact Factor
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    • "The only difference from SCDM is that the expansion rate increases at late times, and this is sufficient to bring predictions and observations into agreement. (Although problems appear to remain with structures on large scales [27] [28] [29] [30] [31].) This is worth – 3 – emphasizing: anything which changes the expansion rate and the corresponding distances at late times by the right amount (and which does not modify other things too much) will account for all of the observed discrepancies, whether of luminosities of supernovae, anisotropies of the cosmic microwave background (CMB), growth rate of structures or other probes. "
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    Annual Review of Nuclear and Particle Science 12/2011; 62(1). DOI:10.1146/annurev.nucl.012809.104435 · 11.26 Impact Factor
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    ABSTRACT: Statistical isotropy (SI) has been one of the simplifying assumptions in cosmological model building. Experiments like WMAP and PLANCK are attempting to test this assumption by searching for specific signals in the Cosmic Microwave Background (CMB) two point correlation function. Modifications to this correlation function due to gravitational lensing by the large scale structure (LSS) surrounding us have been ignored in this context. Gravitational lensing will induce signals which mimic isotropy violation even in an isotropic universe. The signal detected in the Bipolar Spherical Harmonic (BipoSH) coefficients $A^{20}_{ll}$ by the WMAP team may be explained by accounting for the lensing modifications to these coefficients. Further the difference in the amplitude of the signal detected in the V-band and W-band maps can be explained by accounting for the differences in the designed angular sensitivity of the instrumental beams. The arguments presented in this article have crucial implications for SI violation studies. Constraining SI violation will only be possible by complementing CMB data sets with all sky measurements of the large scale dark matter distribution. Till that time, the signal detected in the BipoSH coefficients from WMAP-7 could also be yet another suggested evidence of strong deviations from the standard $\Lambda$CDM cosmology based on homogeneous and isotropic FRW models.
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