a real cosmological field (whose nature is yet to be investigated) which naturally defines a privileged frame, most likely corresponding to the co-moving frame of the universe. Hence we see no contradiction in analyzing relativistic phenomena with the CSL model. For attempts towards a fully relativistic formulation of collapse models, one can refer to [@Tu; @Bedingham].

The transition amplitude
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In the more general approach to the problem of neutrino oscillations, we consider $n$ flavour eigenstates, which will be labeled by greek subscripts $\left|\nu_{\alpha}\right\rangle$ and each of them is a linear combination of $n$ mass eigenstates that will be labeled by latin subscripts $\left|\nu_{j}\right\rangle$: $$\left|\nu_{\alpha}\right\rangle =\sum_{j=1}^{n}\text{U}_{\alpha j}\left|\nu_{j}\right\rangle.$$ Here, $\text{U}$ is the $n\times n$ mixing matrix, which relates the two different bases; since the flavour eigenstates are supposed to be orthonormal, as well as the mass eigenstates, $\text{U}$ must be unitary.

We take a neutrino in an initial flavour eigenstate, and compute the probability of finding it in another flavour eigenstate, after some time $t$, assuming that the dynamics is governed by the Hamiltonian $H_{\text{\tiny TOT}}$. We assume that the neutrino has definite initial and final momenta. This means that its initial and final states are plane waves and that both 