SMA and ALMA Studies of Disk- and Planet Formation around Low-mass
  Protostars
  We report our current SMA and ALMA studies of disk and planet formation
around protostars. We have revealed that $r \gtrsim$100 AU scale disks in
Keplerian rotation are ubiquitous around Class I sources. These Class I
Keplerian disks are often embedded in rotating and infalling protostellar
envelopes. The infalling speeds of the protostellar envelopes are typically
$\sim$ 3-times smaller than the free-fall velocities, and the rotational
profiles follow the $r^{-1}$ profile, that is, rotation with the conserved
specific angular momentum. Our latest high-resolution ($\sim$0$\farcs$5) ALMA
studies, as well as the other studies in the literature, have unveiled that $r
\sim$100-AU scale Keplerian disks are also present in several Class 0
protostars, while in the other Class 0 sources the inferred upper limits of the
Keplerian disks are very small ($r \lessim$20 AU). Our recent data analyses of
the ALMA long baseline data of the Class I-II source HL Tau have revealed gaps
in molecular gas as well as in dust in the surrounding disk, suggesting the
presence of sub-Jovian planets in the disk. These results imply that disk and
planet formation should be completed in the protostellar stage.
