In the theory of grand unification of particle physics, and, in particular, in theories of neutrino masses and neutrino oscillation, the seesaw mechanism is a generic model used to understand the relative sizes of observed neutrino masses, of the order of eV, compared to those of quarks and charged leptons, which are millions of times heavier. The name of the seesaw mechanism was given by Tsutomu Yanagida in a Tokyo conference in 1981.
There are several types of models, each extending the Standard Model. The simplest version, "Type 1", extends the Standard Model by assuming two or more additional right-handed neutrino fields
inert under the electroweak interaction,[a]
and the existence of a very large mass scale. This allows the mass scale to be identifiable with the postulated scale of grand unification.
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