Effect of collisions on neutrino flavor inhomogeneity in a dense neutrino gas

Understand

We investigate the stability, with respect to spatial inhomogeneity, of a two-dimensional dense neutrino gas.

• The system exhibits growth of seed inhomogeneity due to nonlinear coherent neutrino self-interactions.
• In the absence of incoherent collisional effects, we observe a dependence of this instability growth rate on the neutrino mass spectrum: the normal neutrino mass hierarchy exhibits spatial instability over a larger range of neutrino number density compared to that of the inverted case.
• We further consider the effect of elastic incoherent collisions of the neutrinos with a static background of heavy, nucleon-like scatterers.