  We investigate the hemispherical power asymmetry in the cosmic microwave
background on small angular scales. We find an anomalously high asymmetry in
the multipole range l=601-2048, with a naive statistical significance of 6.5
sigma. However, we show that this extreme anomaly is simply a coincidence of
three other effects, relativistic power modulation, edge effects from the mask
applied, and inter-scale correlations. After correcting for all of these
effects, the significance level drops to ~1 sigma, i.e., there is no anomalous
intrinsic asymmetry in the small angular scales. Using this null result, we
derive a constraint on a potential dipolar modulation amplitude, A(k)<0.0045 on
the ~10 Mpc-scale, at 95% C.L. This new constraint must be satisfied by any
theoretical model attempting to explain the hemispherical asymmetry at large
angular scales.
