Black Hole Mergers from Hierarchical Triples in Dense Star Clusters
  Hierarchical triples are expected to be produced by the frequent
binary-mediated interactions in the cores of globular clusters. In some of
these triples, the tertiary companion can drive the inner binary to merger
following large eccentricity oscillations, as a result of the eccentric
Kozai-Lidov mechanism. In this paper, we study the dynamics and merger rates of
black hole (BH) hierarchical triples, formed via binary--binary encounters in
the CMC Cluster Catalog, a suite of cluster simulations with present-day
properties representative of the Milky Way's globular clusters. We compare the
properties of the mergers from triples to the other merger channels in dense
star clusters, and show that triple systems do not produce significant
differences in terms of mass and effective spin distribution. However, they
represent an important pathway for forming eccentric mergers, which could be
detected by LIGO--Virgo/KAGRA (LVK), and future missions such as LISA and
DECIGO. We derive a conservative lower limit for the merger rate from this
channel of $0.35$ Gpc$^{-3}$yr$^{-1}$ in the local Universe and up to $\sim9\%$
of these events may have a detectable eccentricity at LVK design sensitivity.
Additionally, we find that triple systems could play an important role in
retaining second-generation BHs, which can later merge again in the core of the
host cluster.
