Emergent large flavor mixing from canonical and inverse seesaws?

TL;DR

This paper explores how large neutrino flavor mixing can emerge naturally from canonical and inverse seesaw mechanisms, analyzing their mass relations and the implications for neutrino mass scales and mixing.

Contribution

It introduces a cross seesaw framework that explains large flavor mixing as an emergent phenomenon within canonical and inverse seesaw models.

Findings

Large flavor mixing can emerge from seesaw mechanisms.

Inverse seesaw can lower heavy neutrino mass scales.

Comparison of approximate and exact seesaw relations.

Abstract

While the canonical seesaw mechanism provides a most natural qualitative interpretation of tiny masses for the three active neutrinos, it offers no explanation for their large flavor mixing effects. The latter can be regarded as an emergent consequence of this mechanism, in which case we are left with an intriguing cross seesaw framework in the mass basis of all the six Majorana neutrinos. To lower the mass scales of heavy neutrinos, one is motivated to invoke the inverse seesaw mechanism but has to pay the price for a fine-tuned cancellation between its two sets of new degrees of freedom, in which case the largeness of active flavor mixing is an emergent phenomenon as well. A comparison between the approximate seesaw relations in the flavor basis and those exact ones in the mass basis is also made.