Spins of primordial black holes formed in the matter-dominated phase of
  the Universe
  Angular momentum plays very important roles in the formation of PBHs in the
matter-dominated phase if it lasts sufficiently long. In fact, most collapsing
masses are bounced back due to centrifugal force, since angular momentum
significantly grows before collapse. As a consequence, most of the formed PBHs
are rapidly rotating near the extreme value $a_{*}=1$, where $a_{*}$ is the
nondimensional Kerr parameter at their formation. The smaller the density
fluctuation $\sigma_{H}$ at horizon entry is, the stronger the tendency towards
the extreme rotation. Combining the effect of angular momentum with that of
anisotropy, we estimate the black hole production rate. We find that the
production rate suffers from suppression dominantly due to angular momentum for
a smaller value of $\sigma_{H}$, while due to anisotrpopy for a larger value of
$\sigma_{H}$. We argue that matter domination significantly enhances the
production of PBHs despite the suppression. If the matter-dominated phase does
not last so long, the effect of the finite duration significantly suppresses
PBH formation and weakens the tendency towards large spins. (abridged)
