The Cross-correlation of KSZ Effect and 21 cm Intensity Mapping with
  Tidal Reconstruction
  We discuss the possibility of studying diffuse baryon distributions with
kinematic Sunyaev-Zel'dovich (kSZ) effect by correlating cosmic microwave
background (CMB) temperature fluctuations with density fluctuations from 21\,cm
intensity mapping (IM). The biggest challenge for the cross-correlation is the
loss of large-scale information in IM, due to foregrounds and the zero spacing
problem of interferometers. We apply the tidal reconstruction algorithm to
restore the lost large-scale modes, which increases the correlation by more
than a factor of three. With the predicted foreground level, we expect a
$\sim20\,\sigma$ detection of kSZ signal for $0.8\lesssim z\lesssim2.5$ with
CHIME and Planck, and a $\sim40\, \sigma$ detection with HIRAX and Planck. The
significance can be greatly increased with next-generation facilities of higher
spatial resolutions.
