Hemispherical Power Asymmetry

Planck observations reveal a statistically significant asymmetry in CMB temperature power: one hemisphere of the sky, roughly aligned with the ecliptic, contains more power than the opposite hemisphere at the ~3% level across a wide range of multipoles. ΛCDM provides no mechanism for such a large-scale directional asymmetry; the isotropy of inflationary perturbations predicts no preferred hemisphere. In SCT the hemispherical power asymmetry is a direct consequence of the collision impact parameter. A non-zero impact parameter b means that the two pockets did not collide head-on; one side of the overlap volume was swept by the more energetic leading edge of the collision front while the opposite side was swept by the trailing edge. The leading-edge hemisphere received a slightly higher energy density at the moment of thermalization, producing systematically more power in density fluctuations on that side of the sky.

The magnitude of the asymmetry is controlled by the ratio of the impact parameter to the effective collision radius, which SCT does not yet constrain to better than order-of-magnitude precision. However, the angular scale dependence of the asymmetry — strongest at low multipoles where the large-scale geometry is most visible, diminishing at small angular scales where local physics dominates — is a direct prediction of the collision's finite-velocity geometry. The fact that the asymmetry axis is approximately aligned with the Axis of Evil and with the CMB dipole direction further strengthens the case that all three anomalies share the same physical origin: the collision geometry of the original SCT event, rather than three independent statistical flukes.