Where Neutrino Decoherence Lies

Recently, several studies of neutrino oscillations in the vacuum have not found the decoherence long expected from the separation of wave packets of neutrinos in different mass eigenstates. We show that such decoherence will, on the other hand, be present in a treatment including any mechanism which leads to a dependence of the final state on both the neutrino's emission and absorption time. Our demonstration is in the 3+1d $V-A$ model, however the details of this model lead to an overall factor which does not affect our conclusions. This allows us to consider a simpler model. There we show that if the positions of the final state particles are measured, or equivalently entangled with the environment, then decoherence will damp neutrino oscillations. We also show that wave packet spreading can cause the decoherence to eventually saturate, without completely suppressing the oscillations.