CMB Anomalies after Planck (1510.07929v1)

Abstract: Several unexpected features have been observed in the microwave sky at large angular scales, both by WMAP an by Planck. Among those features is a lack of both variance and correlation on the largest angular scales, alignment of the lowest multipole moments with one another and with the motion and geometry of the Solar System, a hemispherical power asymmetry or dipolar power modulation, a preference for odd parity modes and an unexpectedly large cold spot in the Southern hemisphere. The individual p-values of the significance of these features are in the per mille to per cent level, when compared to the expectations of the best-fit inflationary $\Lambda$CDM model. Some pairs of those features are demonstrably uncorrelated, increasing their combined statistical significance and indicating a significant detection of CMB features at angular scales larger than a few degrees on top of the standard model. Despite numerous detailed investigations, we still lack a clear understanding of these large-scale features, which seem to imply a violation of statistical isotropy and scale invariance of inflationary perturbations. In this contribution we present a critical analysis of our current understanding and discuss several ideas of how to make further progress.

• The paper identifies significant CMB anomalies such as a lack of large-angle correlation, unexpected multipole alignments, and hemispherical power asymmetry.
• The analysis compares WMAP and Planck datasets to statistically isolate these deviations from the standard ΛCDM cosmological predictions.
• Findings suggest potential new physics including modifications to inflationary theory and warrant further observational studies to refine our cosmic understanding.

Analyzing CMB Anomalies in the Wake of Planck Observations

The paper conducted by Schwarz, Copi, Huterer, and Starkman offers an analytical overview of observed anomalies in the cosmic microwave background (CMB) following data from the Planck satellite. The anomalies discussed highlight potential deviations from the expected isotropic and homogeneous characteristics predicted by the standard $\Lambda$CDM cosmological model. These deviations manifest in several unexpected features at large angular scales, demanding a re-evaluation of our understanding of the CMB.

Observational Anomalies:

1. Lack of Large-Angle Correlation: The paper reports a significant lack of correlation at angular scales greater than 60 degrees. This was first noticed in the data from the Wilkinson Microwave Anisotropy Probe (WMAP) and confirmed by Planck. This anomaly suggests a severe underrepresentation of power at these scales, quantified by low variance and a corresponding lack of angular correlation.
2. Alignment of Low Multipole Moments: The analysis identifies a surprising alignment of low multipole moments (specifically the quadrupole and octopole) with each other and with the geometry of the solar system. This alignment potentially indicates a preferred direction in the universe, contrary to the expectations of statistical isotropy inherent in the $\Lambda$CDM model.
3. Hemispherical Power Asymmetry: There exists an asymmetry in power distribution between hemispheres in large-scale CMB, indicating a dipolar modulation in the temperature data. This could imply an anisotropic perturbation in the early universe.
4. Odd Parity Preference and the Cold Spot: A preference for odd parity modes and the observation of a distinct cold spot in the southern hemisphere further suggest discordance with the standard model and require exploration of non-Gaussian features.

Statistical Significance and Interactions:

The paper argues for the independence of these anomalies, indicating that they are not merely correlated artifacts but statistically significant features that may require distinct explanations. Given the improbability of these anomalies occurring concurrently by chance within the $\Lambda$CDM framework, they present a compelling case for new physics or undiscovered cosmological phenomena.

Implications for Theoretical and Practical Developments:

These anomalies challenge the prevailing cosmological orthodoxy, opening pathways for different theoretical interpretations including:

• Modifications to inflationary theory to account for broken isotropy or scale invariance.
• The influence of local structures or foregrounds impacting the CMB signal.
• Potential relics from pre-inflationary phases or alternative topological configurations that contribute to non-trivial correlations.

Practically, further investigations into these anomalies could refine CMB data interpretations, impacting our understanding of the universe's inception and evolution. This necessitates interdisciplinary approaches, combining insights from CMB polarization studies, large-scale structure surveys, and analyses of potential solar and galactic foregrounds.

Future Prospects:

As the paper elucidates, forthcoming experiments focusing on polarization or improved galaxy distribution mapping may shed critical light on these mysteries. Future missions, such as those proposed by CMB-S4 and others, are well-positioned to deepen our understanding by providing more granular data, potentially correlating CMB features with large-scale structures in an effort to unravel these cosmic anomalies.

In conclusion, the anomalies highlighted by the authors stand as intriguing challenges to the $\Lambda$CDM model, inviting robust theoretical and observational follow-up. The pursuit of understanding these features may well propel significant advancements in cosmological physics, potentially uncovering new insights about the fabric and history of our universe.