Parity asymmetry in the CMBR temperature power spectrum

Abstract

We study the power asymmetry between even and odd multipoles in the multipolar expansion of cosmic microwave background temperature data from the Wilkinson Microwave Anisotropy Probe (WMAP), recently reported in the literature. We introduce an alternate statistic which probes this effect more sensitively. We find that the data are highly anomalous and consistently outside the 2σ significance level in the whole multipole range l = [2, 101]. We examine the possibility that this asymmetry may be caused by the foreground cleaning procedure or by residual foregrounds. By direct simulations we rule out this possibility. We also examine several possible subdominant foregrounds, which might lead to such an asymmetry. However, in all cases we are unable to explain the signal seen in data. We next examine cleaned maps, using procedures other than that followed by the WMAP science team. In particular, we analysed the maps cleaned by the Internal Powar Spectrum Estimation (IPSE), needlets and the harmonic Internal Linear Combination (ILC) procedures. In all these cases, we also find a statistically significant signal of power asymmetry if the power spectrum is estimated from the masked sky. However, the significance level is found to be not as high as that in the case of the WMAP best‐fitting power spectrum. Finally, we test the contribution of low‐l multipoles to the observed power asymmetry. We find that if we eliminate the first six multipoles, l = [2, 7], the significance falls below the 2σ confidence level. Hence, we find that the signal gets dominant contribution from low‐l modes.

Asymmetries in the angular distribution of the cosmic microwave background

“…Recently, Aluri & Jain (2012) analyzed in detail the signature of parity asymmetry first found by Kim & Naselsky (2010) in the WMAP best-fit temperature power spectrum, confirming this Article published by EDP Sciences A121, page 1 of 6 asymmetry on a 3-σ level. Aluri & Jain (2012) also concluded that their result is not due to residual foregrounds or to foreground cleaning.…”

“…Aluri & Jain (2012) also concluded that their result is not due to residual foregrounds or to foreground cleaning. In addition, the preferred direction of the parity asymmetry coincides with the CMB kinematic dipole, showing that it may somehow be related to the quadrupole-octopole alignment (Naselsky et al 2012).…”

BeyondΛCDM: Problems, solutions, and the road ahead

“…The cosmic microwave background data released by the Planck Satellite [480,16] confirms the existence of several large-scale statistical "anomalies" in the temperature maps, most of which were also observed in the WMAP data. Amongst these, the most robust seem to be: the quadrupole-octupole alignment [491,492,483,484,485,487,489]; the hemispherical asymmetry in power between the "northern" and "southern" hemispheres [476,477,493,478,479,480,481,16]; the existence of a Cold Spot [494,495,496,16]; the lack of angular correlation between separations of 60 degrees and larger [486,487,488,480]; and the point-parity asymmetry [497,498,499,500,501,16]. If not due to statistical flukes [502], these anomalies represent both the possibility of new physics at high energy scales and/or a hint of unknown systematics in the map-cleaning procedure (see e.g.…”

Directional dependence of CMB parity asymmetry

“…However, similar to the WMAP data [4], a number of anomalies has been reported in the CMB low multipoles [5], including the low quadrupole, the alignment of the quadrupole and octopole, the missing angular power at large scale and so on. Among them, the parity asymmetry of the CMB low multipoles has also been investigated in both WMAP and Planck data [5][6][7][8][9][10][11], showing significant dominance of the power spectrum stored in the odd multipoles over the even ones. This anomaly of CMB may imply the physics of the early Universe [12,13], the nontrivial topology [14,15], some foreground residuals [10,16] or systematic errors [17].…”