  Once a light axionlike scalar field couples to the electroweak gauge bosons,
its classical motion during reheating induces an effective chemical potential
for the fermion number. In the presence of rapid lepton number (L)-violating
processes in the plasma, such a chemical potential provides a favorable
opportunity for baryogenesis via leptogenesis. We are able to demonstrate that
L violation due to the exchange of heavy Majorana neutrinos is sufficient for a
successful realization of this idea. Our mechanism represents a novel and
minimal alternative to thermal leptogenesis, which turns out to be insensitive
to the masses and CP-violating phases in the heavy neutrino sector. It is
consistent with heavy neutrino masses close to the scale of grand unification
and, quite complementary to thermal leptogenesis, requires the reheating
temperature to be at least of order 10^12 GeV.
