Physics Theory Seminar with Josh Martin on Loss of Flavor Coherence in a Dense Neutrino Gas

In a dense neutrino gas, coherent forward scattering among neutrinos generates a potential which can be modeled as an all-to-all coupled spin-spin interaction. This potential generically introduces entanglement in the quantum many-body system. We study the evolution of such a system and compare it with the typically employed mean-field approximation for a small number of neutrinos (N = 16). We consider randomly chosen couplings in the Hamiltonian and the evolution of several initial product states. We observe a loss of coherence in one- and two-body trace-reduced partitions of the many-body system and substantial disagreement between the quantum many-body system and the mean-field approximation to it. This suggests that the many-body evolution may be well approximated as a classical mixture of separable states.