Once-in-a-lifetime encounter models for neutrino media: Coherent oscillations, quantum decoherence, and flavor equilibria in between

Neutrinos that interact with each other can undergo collective flavor oscillations which are essential to some important astrophysical phenomena. For example, in a core-collapse supernova, collective neutrino oscillations can affect the dynamics of the explosion, the properties of the neutrinos that reach Earth, and the synthesis of the universe's heavy elements. We present the once-in-a-lifetime encounter (OILE) models for the study of collective flavor oscillations in dense neutrino gases. As in real astrophysical scenarios, a pair of neutrinos in an OILE model may interact only once in their lifetimes. OILE models agree with the mean-field limit, and with other many-body models, in opposite limits, respectively. Meanwhile, they also have some unique dynamics of their own. In particular, in between these two limits, the models evolve along a path of mean-field equilibria, adiabatically driven by the collisional effect due to entanglement.