http://arxiv.org/abs/1408.5792
We perform an analysis of the CMB temperature data taken by the Planck satellite investigating if there is any significant deviation from cosmological isotropy. We look for differences between two opposite hemispheres with respect to particular directions, comparing with simulations. We apply a mask symmetrized in antipodal directions to avoid possible biases and smoothed on a 10′ scale to avoid spurious extra power on small scales induced by sharp edges. We properly take into account of Doppler and aberration effects due to our peculiar velocity and of the anisotropy of the noise, since these effects induce a significant “hemispherical asymmetry”. We are thus able to probe scales all the way to $\ell = 2000$. After such treatment we find no evidence for significant hemispherical anomalies along any of the analyzed directions (i.e., deviations are less than 2$\sigma$ in the full range of $\ell$). Then we find results on a “dipolar modulation” of the the power spectrum of amplitude $A_{mod}$. Along the most asymmetric direction we find $A_{mod} = 0.0044 \pm 0.0014$ for $1 < \ell < 2000$, which represents a 3.3$\sigma$ discrepancy compared to simulations. If taking into account of the extra parameter the dipolar modulation model is preferred over the isotropic model with a $2.6 \sigma$ preference. However this is an overestimate of the real statistical significance, because of the a posteriori choice of such a direction. Interestingly, without proper removal of Doppler and aberration effects there are spurious discrepancies at high $\ell$ which can go up to 4.9$\sigma$ for the dipolar modulation. Even when considering only $\ell < 600$ we find that the boost is non-negligible and alleviates the discrepancy on the modulation from 3.3$\sigma$ to 2.9$\sigma$.
M. Quartin and A. Notari
Tue, 26 Aug 14
25/59
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