Fast flavor instability in hypermassive neutron star disk outflows

We examine the effect of neutrino flavor transformation by fast instability (FFI) on long-term mass ejection from accretion disks formed after neutron star mergers. Neutrino emission and absorption in disk set composition ejecta, which subsequently undergoes $r$-process nucleosynthesis upon expansion cooling. Here we perform 28 time-dependent, axisymmetric, viscous-hydrodynamic simulations around hypermassive stars (HMNSs) variable lifetime, using a 3-species leakage scheme for an annular-lightbulb absorption. include due FFI parametric way, modifying absorbed fluxes temperatures, allowing mixing at various levels equilibration, also way that aims to respect lepton-number preserving symmetry self-interaction Hamiltonian. find promptly-formed black hole (BH), lowers average electron fraction outflow decrease absorption, driven primarily drop neutrino/antineutrino flux mixing. For long-lived HMNS, emits more heavy lepton neutrinos reabsorbs than BH, with smaller compensated higher temperature The resulting has broader distribution, proton-rich peak, stronger radiative driving. Disks intermediate HMNS lifetimes show results fall between these two limits. In most cases, impact is moderate, changes ejection, velocity, order $\sim 10\%$, lanthanide/actinide up factor 2$.