Isotropic non-Gaussian gNL-like toy models that reproduce cosmic microwave background anomalies

Context. Based on recent observations of the cosmic microwave background (CMB), claims of statistical anomalies in the properties of the CMB fluctuations have been made. Although the statistical significance of the anomalies remains only at the ∼2−3σ significance level, the fact that there are many different anomalies, several of which support a possible deviation from statistical isotropy, has motivated a search for models that provide a common mechanism to generate them. Aims. The goal of this paper is to investigate whether these anomalies could originate from non-Gaussian cosmological models, and to determine what properties these models should have. Methods. We present a simple isotropic, non-Gaussian class of toy models that can reproduce six of the most extensively studied anomalies. We compare the presence of anomalies found in simulated maps generated from the toy models and from a standard model with Gaussian fluctuations. Results. We show that the following anomalies, as found in the Planck data, commonly occur in the toy model maps: (1) large-scale hemispherical asymmetry (large-scale dipolar modulation), (2) small-scale hemispherical asymmetry (alignment of the spatial distribution of CMB power over all scales ℓ = [2, 1500]), (3) a strongly non-Gaussian hot or cold spot, (4) a low power spectrum amplitude for ℓ < 30, including specifically (5) a low quadrupole and an unusual alignment between the quadrupole and the octopole, and (6) parity asymmetry of the lowest multipoles. We note that this class of toy model resembles models of primordial non-Gaussianity characterised by strongly scale-dependent gNL-like trispectra.

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Primordial Non-Gaussianity and Bispectrum Measurements in the Cosmic Microwave Background and Large-Scale Structure

Advances in Astronomy ◽

10.1155/2010/980523 ◽

2010 ◽

Vol 2010 ◽

pp. 1-64 ◽

Cited By ~ 126

Author(s):

Michele Liguori ◽

Emiliano Sefusatti ◽

James R. Fergusson ◽

E. P. S. Shellard

Keyword(s):

Cosmic Microwave Background ◽

Large Scale ◽

Initial Conditions ◽

Temperature Fluctuations ◽

Large Scale Structure ◽

Scale Structure ◽

Future Prospects ◽

Microwave Background ◽

Galaxy Distribution ◽

Non Gaussian

The most direct probe of non-Gaussian initial conditions has come from bispectrum measurements of temperature fluctuations in the Cosmic Microwave Background and of the matter and galaxy distribution at large scales. Such bispectrum estimators are expected to continue to provide the best constraints on the non-Gaussian parameters in future observations. We review and compare the theoretical and observational problems, current results, and future prospects for the detection of a nonvanishing primordial component in the bispectrum of the Cosmic Microwave Background and large-scale structure, and the relation to specific predictions from different inflationary models.

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SAMPLE VARIANCE IN LARGE-SCALE COSMIC MICROWAVE BACKGROUND ANISOTROPY MEASUREMENTS

International Journal of Modern Physics D ◽

10.1142/s0218271898000097 ◽

1998 ◽

Vol 07 (01) ◽

pp. 89-96 ◽

Cited By ~ 1

Author(s):

KIN-WANG NG

Keyword(s):

Correlation Function ◽

Cosmic Microwave Background ◽

Large Scale ◽

Large Angle ◽

Density Fluctuations ◽

Sample Variance ◽

Small Scale ◽

Microwave Background ◽

Cosmic Microwave Background Anisotropy ◽

Computationally Intensive

The effects of limited sky coverage in large-angle cosmic microwave background anisotropy experiments are investigated by computing the variance of the angular two-point correlation function with an incomplete sphere. We find that, assuming a power spectrum of density fluctuations with spectral index n = 1, the Galactic cut of half-width 20° (40°) about the Equator made by the COBE DMR experiment would induce a sample variance on the rms temperature fluctuation [(ΔT/T) rms ]2 (or equivalently, the correlation function at zero lag), which is 12% (38%) greater than the cosmic variance with a whole sky coverage. This result is about two times smaller than the naive expectation that the cosmic variance is enhanced by a factor of [Formula: see text], where A is the solid angle sampled by the experiment. We also find that the sample variance of the correlation function at nonzero lag can approach the cosmic variance limit. Our approach provides an analytic way of finding a theoretical error to the theoretical prediction for a particular experiment (either large- or small-scale), without having recourse to computationally intensive Monte Carlo or maximum likelihood methods.

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Large-Angle Anomalies in the CMB

Advances in Astronomy ◽

10.1155/2010/847541 ◽

2010 ◽

Vol 2010 ◽

pp. 1-17 ◽

Cited By ~ 124

Author(s):

Craig J. Copi ◽

Dragan Huterer ◽

Dominik J. Schwarz ◽

Glenn D. Starkman

Keyword(s):

Cosmic Microwave Background ◽

Low Power ◽

Large Scale ◽

Statistical Significance ◽

Large Angle ◽

Inflationary Cosmology ◽

Microwave Background

We review the recently found large-scale anomalies in the maps of temperature anisotropies in the cosmic microwave background. These include alignments of the largest modes of CMB anisotropy with each other and with geometry and direction of motion of the solar ssystem, and the unusually low power at these largest scales. We discuss these findings in relation to expectation from standard inflationary cosmology, their statistical significance, the tools to study them, and the various attempts to explain them.

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Observations of the Corona Borealis supercluster with the superextended Very Small Array: further constraints on the nature of the non-Gaussian cosmic microwave background cold spot

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2008.13985.x ◽

2008 ◽

Vol 391 (3) ◽

pp. 1127-1136 ◽

Cited By ~ 10

Author(s):

Ricardo Génova-Santos ◽

José Alberto Rubiño-Martín ◽

Rafael Rebolo ◽

Richard A. Battye ◽

Francisco Blanco ◽

...

Keyword(s):

Cosmic Microwave Background ◽

Cold Spot ◽

Microwave Background ◽

Small Array ◽

Non Gaussian

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Non-Gaussian stochastic gravitational waves from phase transitions

Journal of High Energy Physics ◽

10.1007/jhep11(2021)107 ◽

2021 ◽

Vol 2021 (11) ◽

Author(s):

Soubhik Kumar ◽

Raman Sundrum ◽

Yuhsin Tsai

Keyword(s):

Phase Transitions ◽

Cosmic Microwave Background ◽

Gravitational Wave ◽

Gravitational Waves ◽

Large Scale ◽

Large Scale Structure ◽

Scale Structure ◽

Microwave Background ◽

Gravitational Wave Detectors ◽

Non Gaussian

Abstract Cosmological phase transitions in the primordial universe can produce anisotropic stochastic gravitational wave backgrounds (GWB), similar to the cosmic microwave background (CMB). For adiabatic perturbations, the fluctuations in GWB follow those in the CMB, but if primordial fluctuations carry an isocurvature component, this need no longer be true. It is shown that in non-minimal inflationary and reheating settings, primordial isocurvature can survive in GWB and exhibit significant non-Gaussianity (NG) in contrast to the CMB, while obeying current observational bounds. While probing such NG GWB is at best a marginal possibility at LISA, there is much greater scope at future proposed detectors such as DECIGO and BBO. It is even possible that the first observations of inflation-era NG could be made with gravitational wave detectors as opposed to the CMB or Large-Scale Structure surveys.

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Anomalies in the Cosmic Microwave Background and Their Non-Gaussian Origin in Loop Quantum Cosmology

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2021.703845 ◽

2021 ◽

Vol 8 ◽

Author(s):

Ivan Agullo ◽

Dimitrios Kranas ◽

V. Sreenath

Keyword(s):

Cosmic Microwave Background ◽

Quantum Cosmology ◽

Statistical Significance ◽

New Physics ◽

Common Origin ◽

Loop Quantum Cosmology ◽

Microwave Background ◽

Λcdm Model ◽

Non Gaussian ◽

Dipolar Modulation

Anomalies in the cosmic microwave background (CMB) refer to features that have been observed, mostly at large angular scales, and which show some tension with the statistical predictions of the standard ΛCDM model. In this work, we focus our attention on power suppression, dipolar modulation, a preference for odd parity, and the tension in the lensing parameter AL. Though the statistical significance of each individual anomaly is inconclusive, collectively they are significant, and could indicate new physics beyond the ΛCDM model. In this article, we present a brief, but pedagogical introduction to CMB anomalies and propose a common origin in the context of loop quantum cosmology.

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Cosmic Tango Between the Very Small and the Very Large: Addressing CMB Anomalies Through Loop Quantum Cosmology

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2021.685288 ◽

2021 ◽

Vol 8 ◽

Author(s):

Abhay Ashtekar ◽

Brajesh Gupt ◽

V. Sreenath

Keyword(s):

Power Spectrum ◽

Quantum Gravity ◽

Cosmic Microwave Background ◽

Quantum Cosmology ◽

Large Scale ◽

Loop Quantum Gravity ◽

Statistical Significance ◽

Loop Quantum Cosmology ◽

Microwave Background

While the standard, six-parameter, spatially flat ΛCDM model has been highly successful, certain anomalies in the cosmic microwave background bring out a tension between this model and observations. The statistical significance of any one anomaly is small. However, taken together, the presence of two or more of them imply that according to standard inflationary theories we live in quite an exceptional Universe. We revisit the analysis of the PLANCK collaboration using loop quantum cosmology, where an unforeseen interplay between the ultraviolet and the infrared makes the primordial power spectrum scale dependent at very small k. Consequently, we are led to a somewhat different ΛCDM Universe in which anomalies associated with large scale power suppression and the lensing amplitude are both alleviated. The analysis also leads to new predictions for future observations. This article is addressed both to cosmology and loop quantum gravity communities, and we have attempted to make it self-contained.

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STOCHASTIC STABILIZATION OF CHAOS AND THE COSMIC MICROWAVE BACKGROUND

International Journal of Modern Physics D ◽

10.1142/s0218271804005699 ◽

2004 ◽

Vol 13 (07) ◽

pp. 1461-1467 ◽

Cited By ~ 2

Author(s):

C. P. DETTMANN ◽

J. P. KEATING ◽

SANDRA D. PRADO

Keyword(s):

Cosmic Microwave Background ◽

Gaussian Distribution ◽

Big Bang ◽

Microwave Background ◽

Stochastic Stabilization ◽

Physical Mechanisms ◽

Quantum Wave ◽

Non Gaussian ◽

Cmb Fluctuations ◽

The Big Bang

The cosmic microwave background (CMB) is a contemporary echo of the Big Bang. The recently announced WMAP 1-year sky maps1 provide exceptionally accurate data for the CMB, making it possible to probe the physics of the early Universe down to an unprecedented level of detail. Fluctuations in the CMB have a distribution that is close to Gaussian (i.e. normal).2 There has been considerable interest in identifying physical mechanisms that might lead to deviations from the Gaussian distribution.2,3 One class of cosmological models that have been much studied are those in which the Universe has constant negative curvature; all photon trajectories are then exponentially unstable and the Gaussian distribution of the CMB fluctuations has been related to general properties of quantum wave-functions in chaotic systems.4–6 Inhomogeneities in the distribution of matter imply a non-constant curvature. Here we show that, surprisingly, random perturbations in the curvature can stabilize photon trajectories. We argue that this leads to quantifiable non-Gaussian fluctuations in the CMB, as well as having other potentially important cosmological consequences.

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