Spin excitonic and diffusive modes in superfluid Fermi liquids

A role of a particle-particle p-wave spin interaction in Fermi liquids with s-wave pairing is studied. Depending on the sign of the interaction there arises either the new exciton collective mode below the pair-breaking threshold or the diffusive excitation mode above the threshold. The Landau parameters which control the interaction strength are evaluated for various systems: the dilute fermion gases, degenerate electron liquid, metals, atomic nuclei and neutron matter. The interaction removes also the square-root singularity in the phase space of pair breaking processes. It is shown how these effects influence the neutrino emissivity in the neutron Cooper-pair recombinations in neutron stars.