HEP
In the literature: open
What mechanism generates neutrino masses?
In plain words
Neutrinos are at least a million times lighter than the electron. They could get mass like other particles but with a tiny coupling, or through a seesaw with very heavy partner particles.
Precise statement
Identify the origin of $m_{\nu} < \sim 0.1\ \mathrm{eV}$: Dirac Yukawas with $y \sim 1e-12$ plus right-handed neutrinos, the type I, II or III seesaw ($m_{\nu} \sim y^2 v^2 / M$), or radiative and low-scale mechanisms. An answer is the mechanism together with its scale, confirmed by a signature such as lepton number violation or heavy neutral leptons.
What would settle it
Observation of neutrinoless double beta decay plus identification of the associated new states or interactions at colliders or in rare decays.
Related problems
- More general than Are neutrinos Majorana particles, their own antiparticles?