Speaker
Description
In the canonical seesaw framework flavor mixing and CP violation in weak charged current interactions of light and heavy Majorana neutrinos are correlated with each other and described respectively by the $3\times 3$ matrices $U$ and $R$. We show that the very possibility of $\big|U^{}_{\mu i}\big| = \big|U^{}_{\tau i}\big|$ (for $i = 1, 2, 3$), which is strongly indicated by current neutrino oscillation data as a good approximation, automatically leads to a novel relation $\big|R^{}_{\mu i}\big| = \big|R^{}_{\tau i}\big|$ (for $i = 1, 2, 3$). We show that behind these two sets of equalities and the experimental evidence for leptonic CP violation lies a minimal flavor symmetry: the overall neutrino mass term keeps invariant when the left-handed neutrino fields transform as $\nu^{}_{e \rm L} \to (\nu^{}_{e \rm L})^c$, $\nu^{}_{\mu \rm L} \to (\nu^{}_{\tau \rm L})^c$, $\nu^{}_{\tau \rm L} \to (\nu^{}_{\mu \rm L})^c$ and the right-handed neutrino fields undergo an arbitrary unitary CP transformation. Such a generalized $\mu$-$\tau$ reflection symmetry, together with the fact that all the active-sterile flavor mixing angles in $R$ are expected to be considerably smaller than the active flavor mixing angles in $U$, provides an intriguing illustration of the emergence of a cross seesaw system for both neutrino masses and flavor mixing effects of Majorana neutrinos.
