Comparison between hemisphere comparison method and dipole-fitting
  method in tracing the anisotropic expansion of the Universe use the Union2
  dataset
  Type-Ia supernovae (SNe Ia) are often used as the standard candles to probe
the anisotropic expansion of the Universe. In this paper, we make a
comprehensive comparison between the hemisphere comparison (HC) method and
dipole-fitting (DF) method in searching for the cosmological preferred
direction using the Union2 dataset, a compilation of 557 well-calibrated SNe
Ia. We find that the directions of the faintest SNe Ia derived from these two
methods are approximately opposite. Monte Carlo simulations show that the
results of the HC method strongly depend on the distribution of the data points
in the sky. The coincidence that the HC method and DF method give two
completely opposite directions may be due to the extremely nonuniform
distribution of the Union2 dataset.
