lightest stellar progenitors (see, e.g., @janka2012a for a recent review).

Successful neutrino-driven explosions require additional assistance by non-spherical hydrodynamic instabilities that increase the efficiency of neutrino energy deposition. This phenomenon has been observed in numerous two-dimensional (e.g., @herant94 [@burrows95; @janka96; @mezzacappa98; @scheck06; @ohnishi06; @buras06b; @burrows07; @murphy08; @ott08; @marek09; @suwa09; @mueller2012; @couch2013]) as well as three-dimensional (e.g., @iwakami08 [@nordhaus10a; @hanke2012; @burrows2012; @emueller2012; @takiwaki2012; @ott2012b; @couch2012; @dolence2013; @hanke2013]) core-collapse simulations of various levels of sophistication. In addition to assisting the onset of explosion, these instabilities can contribute to the generation of pulsar kicks [@scheck06; @nordhaus10b; @wongwathanarat2010], the spin-up of the forming neutron star [@fryer07; @blondin07a; @blondin07b; @F10] and the seeding of late-time asymmetries [@kifonidis06; @hammer2010; @wongwathanarat2012].

The shock-neutrinosphere cavity is unstable to *convection* driven by the energy deposition from neutrinos emitted in deeper layers (e.g., @bethe90). This process generates kinetic energy on spatial scales comparable to or smaller than the size of the neutrino heating region. Work by @BM03 and @BM06 isolated a distinct, global oscillatory instability of the standing accretion shock that operates independent of neutrino heating, the so-called Standing Accretion Shock Instability (SASI). The driving mechanism involves an unstable cycle of advected and acoustic perturbations trapped within the shock-neutrinosphere cavity 