Kavli Affiliate: Craig Hogan
| First 5 Authors: Craig Hogan, Ohkyung Kwon, Stephan S. Meyer, Nathaniel Selub, Frederick Wehlen
| Summary:
The global isotropy of the universe is analyzed on the scale of the cosmic
horizon, using the angular correlation function $C(Theta)$ of cosmic microwave
background (CMB) temperature at large angular separation $Theta$. Even-parity
correlation $C_{rm even}(Theta)$ is introduced to obtain a direct, precise
measure of horizon-scale curvature anisotropy independent of the unknown
dipole, with uncertainty dominated by models of Galactic emission. In maps from
{sl Planck}, $C_{rm even}(Theta)$ at $Thetasimeq 90^circpm 15^circ$ is
found to be much closer to zero than previously documented measurements of
correlation, with an absolute value three to four orders of magnitude smaller
than expected in standard theory. Such a small variation from zero is estimated
to occur by chance in a fraction $simeq 10^{-4.3}$ to $simeq 10^{-2.8}$ of
standard realizations. We consider an alternative interpretation of this
result, as a signature of a scale-invariant angular symmetry of cosmological
initial conditions. An example of such a symmetry is formulated geometrically,
by assuming that quantum fluctuations during inflation have spacelike coherence
bounded by compact causal diamonds, and become classical perturbations when
world lines cross inflationary horizons. It is argued that this interpretation
is inconsistent with the standard theory of initial conditions, but is broadly
consistent with other cosmological measurements, and is subject to further
tests.
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