The Polarization Signature of Local Bulk Flows
  A large peculiar velocity of the intergalactic medium produces a Doppler
shift of the cosmic microwave background with a frequency-dependent quadrupole
term. This quadrupole will act as a source for polarization of the cosmic
microwave background, creating a large-scale polarization anisotropy if the
bulk flow is local and coherent on large scales. In the case where we are near
the center of the moving region, the polarization signal is a pure quadrupole.
We show that the signal is small, but detectable with future experiments for
bulk flows as large as some recent reports.
