### Speaker

### Description

We propose theoretical constraints that fermion masses and mixing angles should respect. These constraints are derived from the dispersion relation obeyed by the box diagrams, which are responsible for the mixing of neutral states, such as the $\mu^-e^+$ and $\mu^+e^-$ mixing . The only assumption is that the electroweak symmetry of the Standard Model is restored at a high energy scale, which can be achieved in, for example, the composite Higgs model. We argue that the mixing phenomenon disappears, as the electroweak symmetry is restored. This disappearance is then taken as the high-energy input for the dispersion relation, whose solution at low energy, i.e., in the symmetry broken phase, leads to the aforementioned constraints. These constraints are powerful enough to discriminate the neutrino mass orderings; the neutrino masses in the normal hierarchy, instead of in the inverted hierarchy or quasi-degenerate spectrum, match the observed PMNS matrix elements. The lepton mixing angles larger than the quark ones are explained by means of the inequality $m_2^2/m_3^2\gg m_s^2/m_b^2$, $m_{2,3}$ being the neutrino masses in the NH and $m_{s,b}$ the quark masses. At last, the solution for the $\tau^-e^+$-$\tau^+e^-$ mixing specifies the mixing angle $\theta_{23}\approx 45^\circ$.