  Observations indicate that large-scale anomalies exist in the fluctuations of
the cosmic microwave background. In these anomalies, the hemispherical power
amplitude asymmetry has a correlation length comparable to that of the
observable universe. We propose that a topological defect created by
spontaneous breaking of the U(1) symmetry prior to inflation generated an
initial phase variation, $\delta \theta$, across the observable region of the
universe. The amplitude of this phase fluctuation is protected by topology if
the defect is inside the horizon, and is frozen by causality if the defect
exits the horizon. After inflation, the phase-corresponding boson field started
to oscillate, when the Hubble rate decreased to a level comparable to the mass
of the boson field. The energy density of the newly created boson particles
varied across the observable universe. The bosons subsequently decayed into
radiation prior to the BBN epoch, and the resulting fluctuations in the energy
density produced the observed power asymmetry. This scenario predicts a
scale-dependent modulation amplitude power asymmetry and in addition, as
topological defects created by phase transitions are a very general phenomenon,
the observed hemispherical asymmetry may be seen as an evidence for the
cosmological inflation.
