Monte-Carlo simulations of black hole mergers in AGN disks: Low
  $\chi_{\rm eff}$ mergers and predictions for LIGO
  Accretion disks around supermassive black holes are promising sites for
stellar mass black hole mergers detectable with LIGO. Here we present the
results of Monte-Carlo simulations of black hole mergers within 1-d AGN disk
models. For the spin distribution in the disk bulk, key findings are: (1) The
distribution of $\chi_{\rm eff}$ is naturally centered around
$\tilde{\chi}_{\rm eff} \approx 0.0$, (2) the width of the $\chi_{\rm eff}$
distribution is narrow for low natal spins. For the mass distribution in the
disk bulk, key findings are: (3) mass ratios $\tilde{q} \sim 0.5-0.7$, (4) the
maximum merger mass in the bulk is $\sim 100-200M_{\odot}$, (5) $\sim 1\%$ of
bulk mergers involve BH $>50M_{\odot}$ with (6) $\simeq 80\%$ of bulk mergers
are pairs of 1st generation BH. Additionally, mergers at a migration trap grow
an IMBH with typical merger mass ratios $\tilde{q}\sim 0.1$. Ongoing LIGO
non-detections of black holes $>10^{2}M_{\odot}$ puts strong limits on the
presence of migration traps in AGN disks (and therefore AGN disk density and
structure) as well as median AGN disk lifetime. The highest merger rate occurs
for this channel if AGN disks are relatively short-lived ($\leq 1$Myr) so
multiple AGN episodes can happen per Galactic nucleus in a Hubble time.
