Missing completely of CMB quadrupole in WMAP data (1203.5720v2)

Abstract: In cosmic microwave background (CMB) experiments, foreground-cleaned temperature maps are still contaminated by the residual dipole due to uncertainties of the Doppler dipole direction and microwave radiometer sidelobe. To obtain reliable CMB maps, such contamination has to be carefully removed from observed data. We have previously built a software package for map-making, residual dipole-contamination removal, and power spectrum estimation from the Wilkinson Microwave Anisotropy Probe (WMAP) raw data. This software has now been significantly improved. With the improved software, we obtain a negative result of CMB quadrupole detection with the WMAP raw data, which is -3.2+-3.5 uK^2 from the seven-year WMAP (WMAP7) data. This result is evidently incompatible with ~1000 uK^2 expected from the standard cosmological model LCDM. The completely missing of CMB quadrupole poses a serious challenge to the standard model and sets a strong constraint on possible models of cosmology. Due to the importance of this result for understanding the origin and early evolution of our universe, the software codes we used are opened for public checking.

• The paper presents a refined analysis of WMAP data that finds a near-null CMB quadrupole value, contradicting the typical ~1000 μK² expectation of the ΛCDM model.
• It employs advanced map-making methodologies, including corrected dipole subtraction and comprehensive template fitting, to mitigate systematic errors.
• These results challenge established cosmological principles, suggesting a need for independent verification and potential revisions of the standard cosmological model.

An Evaluation of the Missing CMB Quadrupole in WMAP Data

In this paper by Liu and Li, the authors present an analysis of the cosmic microwave background (CMB) temperature maps derived from the Wilkinson Microwave Anisotropy Probe (WMAP) data with a novel approach to address systematic errors in quadrupole measurement. Specifically, the focus is on the absence of the CMB quadrupole, detected as a negative result of $-3.2 \pm 3.5\ \mu K^2$, which is sharply lower than the $\sim 1000 \ \mu K^2$ predicted by the standard $\Lambda$CDM model.

Methodological Advances

Liu and Li identified residual dipole contamination as a significant issue affecting the reliability of derived CMB maps, which arises from uncertainties in the Doppler dipole direction and radiometer sidelobe responses. They employed a refined software toolset for map-making, which not only handles map creation, dipole contamination removal, and power spectrum estimation more comprehensively but also addresses previously ignored systematic errors. The robust methodology used includes:

• Calculation of the dipole deviation using revised vector computations for the Doppler dipole signal.
• Implementation of a comprehensive template fitting procedure leveraging deviation template maps ($\Delta T_x$, $\Delta T_y$, and $\Delta T_z$).
• This approach corrects for potential dipole deviation that was not adequately managed in the official WMAP processing.

Data Analysis and Results

Liu and Li applied their improved software to WMAP's raw time-ordered data (TOD) from year one through year seven. The derived quadrupole, after removing dipole contamination, consistently indicated a null or negative value (e.g., WMAP7: $-3.2 \pm 3.5 \ \mu K^2$). This finding, derived across several iterations and verification steps, is statistically significant due to the exceedingly low probability of a zero or negative quadrupole emerging by chance from typical $\Lambda$CDM expectations.

Implications and Future Directions

The implications of the absence of a significant CMB quadrupole are profound, posing a potential challenge to the $\Lambda$CDM model, which assumes a nearly scale-invariant spectrum of primordial density fluctuations. As the quadrupole signifies large-scale spatial temperature fluctuations, its complete absence may indicate shortcomings in the current understanding of the early universe's dynamics or fundamental cosmological principles. Future research needs to:

• Verify these findings with independent datasets and methods, possibly incorporating data from other CMB observatories like Planck.
• Reexamine the standard cosmological model's assumptions, considering alternatives or extensions that accommodate low or absent quadrupole scenarios.
• Open the software and methodology developed for broader scrutiny and application, facilitating community-wide verification and iterative improvement.

The controversy surrounding the missing CMB quadrupole serves as a reminder of the complexities inherent in precise cosmological measurements and the necessity for persistent methodological innovation. This research offers a pivotal step in reassessing accepted cosmological models and highlights the ongoing need for rigorous data re-evaluation in cosmological studies.