Quasiparticle renormalization and pairing correlations in spherical superfluid nuclei

Within the framework of nuclear field theory (NFT), the spectrum of atomic nuclei is described in terms of collective and quasiparticle degrees of freedom, that is, of elementary modes of excitation that are directly related to experiment and of their coupling, whose strength and form factors are the basic ingredients entering in the calculations of absolute cross sections of inelastic and of one-and two-particle transfer reactions. We present a detailed discussion of the solution of the Dyson equation, also known as the Nambu-Gor'kov equations in the case of a superfluid system, which propagates medium polarization processes calculated making use of NFT to all orders of perturbation, resulting in the dressing of quasiparticles and in the induced pairing interaction. The formalism is applied to the superfluid nucleus Sn-120. Results concerning the low-energy spectrum, that is, the quasiparticle strength distribution of the neighboring odd-A nuclei Sn-119 and Sn-121, are presented and compared with the experimental findings.