Effective spin distribution of black hole mergers in triples
  Many astrophysical scenarios have been proposed to explain the several black
hole (BH) and neutron star binary mergers observed via gravitational waves
(GWs) by the LIGO-Virgo collaboration. Contributions from various channels can
be statistically disentangled by mass, spin, eccentricity and redshift
distributions of merging binaries. In this paper, we investigate the signatures
of BH-BH binary mergers induced by a third companion through the Lidov-Kozai
mechanism in triple systems. We adopt different prescriptions for the
supernovae natal kicks and consider different progenitor metallicities and
initial orbital parameters. We show that the typical eccentricity in the LIGO
band is $0.01$-$0.1$ and that the merger rate is in the range $0.008-9 \
\mathrm{Gpc}^{-3}\ \mathrm{yr}^{-1}$, depending on the natal kick prescriptions
and progenitor metallicity. Furthermore, we find that the typical distribution
of effective projected spin is peaked at $\chi_{\rm eff}\sim 0$ with
significant tails. We show that the triple scenario could reproduce the
distribution of $\chi_{\rm eff}$. We find that the triple channel may be
strongly constrained by the misalignment angle between the binary component
spins in future detections with spin precession.
