  The effective Lagrangian for the seesaw model is derived. Besides the usual
dimension-5 operator responsible for light neutrino masses, a dimension-6
operator is included which, for three or less heavy neutrino generations,
provides a generic link between low-energy observables and all physical
parameters of the high-energy seesaw Lagrangian. Leptogenesis can be then
confirmed or ruled out through the measurement of neutrino masses and mixings
and the exotic neutrino couplings originated from the dimension-6 operator.
