  The Casas-Ibarra parametrization is a description of the Dirac neutrino mass
matrix M_D in terms of the neutrino mixing matrix V, an orthogonal matrix O and
the diagonal mass matrices of light and heavy Majorana neutrinos in the type-I
seesaw mechanism. Because M^\dagger_D M_D is apparently independent of V but
dependent on O in this parametrization, a number of authors have taken it for
grant that unflavored leptogenesis has nothing to do with CP violation at low
energies. Here we question this observation by clarifying the physical meaning
of O. We establish a clear relationship between O and the observable
quantities, and find that O does depend on V. Our general conclusion is that
both unflavored leptogenesis and flavored leptogenesis have no direct
connection with low-energy CP violation.
