Abstract. The influence of correlations on the critical temperature and density for the onset of superfluidity in nuclear matter is investigated within the scheme of Nozi~res and Schmitt-Rink [1]. For symmetric nuclear matter a smooth transition from Bose-Einstein condensation (BEC) of deuteronlike bound states at low densities and low temperatures to Bardeen-Cooper-Schrieffer (BCS) pairing at higher densities is described. Compared with the mean field approach a lowering of the critical temperature is obtained for symmetric nuclear matter as well as for pure neutron matter. The Mott transition in symmetric nuclear matter is discussed. Regions in the temperature-density plane are identified where correlated pairs give the main contribution to the composition of the system, so that approximations beyond the quasi-particle picture are requested. 05.30.Fk, 21.65.+f, 74.25.Bt Superfluidity and superconductivity are macroscopic quantum phenomena occuring for fermion systems with attractive interaction. A usual framework for its microscopic description is the BCS theory [2]. The BCS theory is a meanfield approach and describes the occurence of pairing correlations forming the condensate. This pairing becomes at the critical temperature identical with the special case of zero momentum bound states in the low density limit [1]. However, in the normal phase a meanfield theory is in general not capable to describe two-particle correlations, in particular bound states with finite momentum. This general problem applies also to nuclear matter. Nuclear matter has been treated within the BCS approach by several authors, see e.g., [3][4][5]. Of special interest with regard to two-particle correlations are the pairing in the 3Si channel (see, e.g., [6,7]) and the deuteron formation (see, e.g., [8]). In the normal phase there are works on the improvement of the meanfield approach including bound states and on the composition of nuclear matter (see, e.g., [9,10]). PACS:An attempt to include the influence of correlations on the critical temperature was proposed by Nozieres and SchmittRink for electron-hole systems [1]. The authors calculate the onset of superfluidity as a function of the coupling strength in the framework of BCS theory. The results are combined with a simple extension of the virial expansion to obtain a density formula including correlations in the normal phase. A similar density formula for nuclear matter is given by Schmidt et al. [10]. In the weak coupling limit Nozihres and Schmitt-Rink find the ordinary BCS critical temperature. The other limit, the strong coupling, is characterized by the formation of non-interacting bosonic bound states which can undergo a Bose-Einstein condensation with the corresponding critical temperature. A smooth transition from strong to weak coupling is obtained. The open question how to treat correlations (fluctuations) and pairing (superfluidity) consistently has recently been addressed in a number of publications [11][12][13].Within this paper we want to study the relevance of t...

No abstract

Medium modification of scattering properties in interacting Bose systems are considered by solving the Bethe-Salpeter equation. An equation of state for the normal phase (generalized Beth-Uhlenbeck formula) is given using the in-medium phase shifts to include two-particle correlations. Conclusions are drawn for systems of bosonic atoms with repulsive interaction such as sodium 23 Na and rubidium 87 Rb. It is shown that the in-medium scattering length and the absolute value of the in-medium scattering phase shift for low scattering energies increase with density.

No abstract

No abstract