  We propose a novel leptogenesis scenario at the reheating era. Our setup is
minimal in the sense that, in addition to the standard model Lagrangian, we
only consider an inflaton and higher dimensional operators. The lepton number
asymmetry is produced not by the decay of a heavy particle, but by the
scattering between the standard model particles. After the decay of an
inflaton, the model is described within the standard model with higher
dimensional operators. The Sakharov's three conditions are satisfied by the
following way. The violation of the lepton number is realized by the
dimension-5 operator. The complex phase comes from the dimension-6 four lepton
operator. The universe is out of equilibrium before the reheating is completed.
It is found that the successful baryogenesis is realized for the wide range of
parameters, the inflaton mass and reheating temperature, depending on the
cutoff scale. Since we only rely on the effective Lagrangian, our scenario can
be applicable to all mechanisms to generate neutrino Majorana masses.
