Constraints on primordial black holes as dark matter candidates from
  capture by neutron stars
  We investigate constraints on primordial black holes (PBHs) as dark matter
candidates that arise from their capture by neutron stars (NSs). If a PBH is
captured by a NS, the star is accreted onto the PBH and gets destroyed in a
very short time. Thus, mere observations of NSs put limits on the abundance of
PBHs. High DM densities and low velocities are required to constrain the
fraction of PBHs in DM. Such conditions may be realized in the cores of
globular clusters if the latter are of a primordial origin. Assuming that cores
of globular clusters possess the DM densities exceeding several hundred
GeV/cm$^3$ would imply that PBHs are excluded as comprising all of the dark
matter in the mass range $3\times 10^{18} \text{g} \lesssim m_\text{BH}\lesssim
10^{24} \text{g}$. At the DM density of $2\times 10^3$ GeV/cm$^3$ that has been
found in simulations in the corresponding models, less than 5% of the DM may
consist of PBH for these PBH masses.
