  The Heavy Fermion state in UPd2Al3 may be approximately described by a dual
model where two of the three U- 5f electrons are in a localized state split by
the crystalline electric field into two low lying singlets with a splitting
energy of about 6 meV. The third 5f electron has itinerant character and forms
the Heavy Electron bands. Inelastic neutron scattering and tunneling
experiments suggest that magnetic excitons, the collective propagating crystal
field excitations of the localized 5f electrons, mediate superconducting (sc)
pairing in UPd2Al3. A theory for this novel mechanism is developed within a
nonretarded approach. A model for the magnetic exciton bands is analyzed and
compared with experiment. The sc pair potential which they mediate is derived
and the gap equations are solved. It is shown that this mechanism favors an odd
parity state which is nondegenerate due to the combined symmetry breaking by
the crystalline electric field and the AF order parameter. A hybrid model
including the spin fluctuation contribution to the pairing is also discussed.
