  We investigate the collision-induced flavor instability in homogeneous,
isotropic, dense neutrino gases in the two-flavor mixing scenario with
energy-dependent scattering. We uncover a simple expression of the growth rate
of this instability in terms of the flavor-decohering collision rates and the
electron lepton number distribution of the neutrino. This growth rate is common
to the neutrinos and antineutrinos of different energies, and is independent of
the mass-splitting and vacuum mixing angle of the neutrino, the matter density,
and the neutrino density, although the initial amplitude of the unstable
oscillation mode can be suppressed by a large matter density. Our results
suggest that neutrinos are likely to experience collision-induced flavor
conversions deep inside a core-collapse supernova even when both the fast and
slow collective flavor oscillations are suppressed.

High Energy Physics - Phenomenology;High Energy Astrophysical Phenomena;Nuclear Theory