The Distortion of the Cosmic Microwave Background by the Milky Way
  The Milky Way can act as a large-scale weak gravitational lens of the cosmic
microwave background (CMB). We study this effect using a photon ray-tracing
code and a Galactic mass distribution with disk, bulge and halo components. For
an observer at the Sun's coordinates in the Galaxy, the bending of CMB photon
paths is limited to less than one arcsecond, and only for rays that pass within
a few degrees of the Galactic Center. However, the entire sky is affected,
resulting in global distortions of the CMB on large angular scales. These
distortions can cause the low-order multipoles of a spherical harmonic
expansion of the CMB sky temperature to leak into higher-order modes. Thus the
component of the CMB dipole that results from the Local Group's motion relative
to the local cosmic frame of rest contributes to higher-order moments for an
observer in the solar system. With our ray-tracing code we show that the
phenomenon is not sensitive to the specific choice of Galactic potential. We
also quantitatively rule it out as a contributor to CMB anomalies such as power
asymmetry or correlated alignment of low-order multipole moments.
