  Type Ia supernovae (SNe Ia) could arise from mergers of carbon-oxygen white
dwarfs (WDs) triggered by Lidov-Kozai (LK) oscillations in hierarchical
triple-star systems. However, predicted merger rates are several orders of
magnitude lower than the observed SNe Ia rate. The low predicted rates can be
attributed in part to the fact that many potential WD-merger progenitor
systems, with high mutual orbital inclination, merge or interact before the WD
stage. Recently, evidence was found for the existence of natal kicks imparted
on WDs with a typical magnitude of 0.75 km/s. In triples, kicks change the
mutual inclination and in general increase the outer orbit eccentricity,
bringing the triple into an active LK regime at late stages and avoiding the
issue of pre-WD merger or interaction. Stars passing by the triple can result
in similar effects. However, both processes can also disrupt the triple. In
this paper, we quantitatively investigate the impact of WD kicks and flybys on
the rate of WD mergers using detailed simulations. We find that WD kicks and
flybys combine to increase the predicted WD merger rates by a factor of ~2.5,
resulting in a time-integrated rate of ~1.1e-4 Msun^-1. Despite the significant
boost, the predicted rates are still more than one order of magnitude below the
observed rate of ~1e-3 Msun^-1. However, many systematic uncertainties still
remain in our calculations, in particular the potential contributions from
tighter triples, dynamically unstable systems, unbound systems due to WD kicks,
and quadruple systems.
