Enhancement or damping of fast neutrino flavor conversions due to collisions

Understand

Fast neutrino flavor conversion can occur in core-collapse supernovae or compact binary merger remnants when non-forward collisions are also at play, and neutrinos are not fully decoupled from matter.

• This work aims to shed light on the conditions under which fast flavor conversion is enhanced or suppressed by collisions.
• By relying on a neutrino toy model with three angular bins in the absence of spatial inhomogeneities, we consider two angular configurations: The first one with angular distributions of $\nu_e$ and $\bar\nu_e$ that are almost isotropic as expected before complete neutrino decoupling and showing little flavor conversion when collisions are absent.
• The second one with angular distributions of $\nu_e$ and $\bar\nu_e$ that are forward peaked as expected in the free-streaming regime and showing significant flavor conversion in the absence of collisions.