Primordial Black-Hole and Macroscopic Dark-Matter Constraints with LISA
  The detectability of gravitational waves originating from primordial black
holes or other large macroscopic dark-matter candidates inspiraling into
Sagittarius ${\rm A}^{\!*}$ is investigated. It is shown that LISA should be a
formidable machine to detect the stochastic signal from the accumulated
collection of such objects that have been gravitationally captured by
Sgr$\,{\rm A}^{\!*}$, provided they have masses above $\sim
10^{-20}\,M_{\odot}$. This is especially so, if they are the main component of
the dark matter, and the dark-matter density at Sagittarius ${\rm A}^{\!*}$
exceeds its value in the solar-neighborhood. Notably, the window of mass that
is unconstrained by various gravitational lensing arguments and observations,
$2 \times 10^{20}\,{\rm g} \leq m_{\rm DM} \leq 4 \times 10^{24}\,{\rm g}$,
will be accessible. Forecasts are derived for the event rates and signal
strengths as a function of dark-matter mass, assuming that the dark-matter
candidates are not tidally disrupted during the inspiral. This is certainly the
case for primordial black holes, and it shown that it is also very likely the
case for candidate objects of nuclear density.
