1303.5371 (M. Axelsson et al.)

Directional dependence of LCDM cosmological parameters    [PDF]

M. Axelsson, Y. Fantaye, F. K. Hansen, A. J. Banday, H. K. Eriksen, K. M. Gorski

We study the previously discovered hemispherical power asymmetry (Eriksen et al. 2004, Hansen et al. 2004, Hansen et al. 2009) with the WMAP 9-year data. We find that the asymmetry is statistically significant at the 3.2 sigma confidence level for l=2--600, where the data is signal dominated, using the WMAP 9-year KQ85 mask. The preferred asymmetry direction is (l,b)=(227,-27), 44 degrees away from the Ecliptic South Pole. Individual asymmetry axes estimated from six independent multipole ranges are all consistent with this direction. This agreement across a wide range of scales argues against a statistical a-posterior' interpretation of the effect. We estimate cosmological parameters on different parts of the sky and show that the parameters A_s, n_s and \Omega_b are the most sensitive to the asymmetrically distributed power asymmetry. In particular, for the two opposite hemispheres aligned with the preferred asymmetry axis, we find n_s = 0.96 \pm 0.022 and n_s = 0.99 \pm 0.024, respectively.

View original: http://arxiv.org/abs/1303.5371