NONLINEAR SIGMA MODEL APPROACH FOR PHASE DISORDER TRANSITIONS IN CHIRAL GROSS–NEVEU, NAMBU–JONA-LASINIO MODELS AND STRONG-COUPLING SUPERCONDUCTORS

Abstract

We briefly review the nonlinear sigma model approach for the subject of increasing interest: "two-step" phase transitions in the Gross–Neveu and the modified Nambu–Jona-Lasinio models at low N and condensation from pseudogap phase in strong-coupling superconductors. Recent success in describing of "Bose-type" superconductors that possess two characteristic temperatures and a pseudogap above Tc is the development approximately comparable with the BCS theory. One can expect that it should have influence on high-energy physics, similar to impact of the BCS theory on this subject. Although first generalizations of this concept to particle physics were made recently, these results were not systematized. In this review we summarize this development and discuss similarities and differences of the appearance of the pseudogap phase in superconductors and the Gross–Neveu and Nambu–Jona-Lasinio-like models. We discuss its possible relevance for chiral phase transition in QCD and color superconductors. This paper is organized in three parts. In the first part, we briefly review the separation of temperatures of pair formation and pair condensation in strong-coupling and low carrier density superconductors (i.e. the formation of the pseudogap phase). The second part is a review of nonlinear sigma model approach to an analogous phenomenon in the chiral Gross–Neveu model at small N. In the third part we discuss the modified Nambu–Jona-Lasinio model where the chiral phase transition is accompanied by a formation of a phase analogous to the pseudogap phase.