  We introduce a CP violating coupling between the Ricci curvature and the
heavy right handed neutrinos. This splits the Majorana masses of the left and
the right handed heavy neutrinos. When the heavy neutrinos decay, their decay
rates are different into left and right chirality light neutrinos. A time
varying non-zero Ricci curvature can give rise to a net lepton asymmetry. The
source of a non-zero curvature in a radiation era is the quantum fluctations of
primordial fields.
