  Stimulated by the still puzzling competition between spin-singlet and
spin-triplet pairing in nuclei, the 3SD1 neutron-proton pairing is investigated
in the framework of BCS theory of nuclear matter. The medium polarization
effects are included in the single particle spectrum and also in the pairing
interaction starting from the G-matrix, calculated in the
Brueckner-Hartree-Fock approximation. The vertex corrections due to spin and
isospin collective excitations of the medium are determined from the
Bethe-Salpeter equation in the RPA limit, taking into account the tensor
correlations. It is found that the self-energy corrections confine the
superfluid state to very low-density, while remarkably quenching the magnitude
of the energy gap, while the induced interaction has an attractive effect. The
interplay between spin-singlet and spin-triplet pairing is discussed in nuclear
matter as well as in finite nuclei.
