Quantum decoherence in neutrino oscillations was theorized almost 50 years ago, however there is still no clear theoretical understanding of this phenomenon, not even agreement on whether or not it could be observed at all. In all the approaches the dimension of the neutrino wavepacket is a crucial ingredient for decoherence, however such a quantity is very difficult to estimate, and depending on the approximations used, it is possible to obtain very different results.
I will present a model where all the particles, including the source and detector, are treated dynamically and consistently with Quantum Field Theory: decoherence emerges from the time-evolution of the initial state. We found that environmental interactions are a crucial ingredient for decoherence: indeed, the environmental interactions will measure the final states of all the particles produced with the neutrino; this will constrain the position in time and space of the neutrino creation, which in turn will localize the neutrino as well: if we approximate the role of environmental interactions by describing the final states of the source particle with a wavepacket of dimension sigma, the dimension of the neutrino wavepacket is determined as well, as a function of sigma. On the other hand, if the environmental interactions are not present (for example, if the decay happens in vacuum), the daughter particles will be described by plane waves instead: in this case the neutrino is not localized either, and we don't have decoherence.
If the states are evolved dynamically, the dimension of the wavepackets will increase with time; I will show that, if such a spread is taken into account, it can affect decoherence. Moreover, such an effect will depend on the absolute mass of the neutrinos, not on the mass square difference; which could offer a possible way to probe such a parameter by studying the neutrino oscillations.
Talk based on https://arxiv.org/abs/2205.05367