Using the Nambu and Jona-Lasinio model and a version of the model using a Polyakov loop, we expose the composite particles we managed to build with the u, d, s quarks. These are used for the first time to construct mesons. Next, we focus on diquarks. They are employed to model baryons as a bound state of a quark and a diquark, using a static approximation. For all these quoted particles, we stress the study of their masses according to two main parameters: the temperature and the baryonic density. In the framework of these studies, the isospin symmetry is applied, whereas an extra analysis at null temperature and density does not use this approximation. The work includes a comparison with experimental masses or results obtained with other approaches.

The Nambu-Jona-Lasinio Lagrangian offers an explication of the seemingly contradictory observations that (a) the energy loss in the entrance channel of heavy ion reactions is not sufficient to thermalize the system and that (b) the observed hadron cross sections are in almost perfect agreement with hydrodynamical calculations. According to this scenario, a critical opacity develops close to the chiral phase transition which equilibrates and hadronizes the expanding system very effectively. It creates as well radial flow and, if the system is not isotropic, finite upsilon2 values.

The color superconductivity was studied with an adaptation of the Nambu and Jona-Lasinio model (NJL). This one was coupled to a Polyakov loop, to form the PNJL model. A µdependent Polyakov loop potential was considered. An objective of the presented works was to describe the analytical calculations required to establish the equations to be solved, in all of the treated cases. They concerned the normal quark phase, the 2-flavor color-superconducting and the color-flavor-locked phases, in an ( ) ( ) 3 3 f c SU SU × description. The calculationswere performed according to the temperature T , the chemical potentials f µ or according to the densities f ρ , with or without the isospin symmetry. Among the obtained results, it was found that at low T , the restoration of the chiral symmetry, the deconfinement transition and the transition between the normal quark and 2-flavor color-superconducting phases occur via first order phase transitions at the same chemical potential. Moreover, an sSC phase was identified in the , q s ρ ρ plane.PACS numbers: 11.10. Wx, 11.30.Rd, 25.75.Nq ( )3 flavor SU description, one mainly mentions the 2-flavor color-superconducting (2SC) phase, in which u and d quarks form pairs, and the color-flavor-locked (CFL) phase that involves ud, us and ds pairs. Other phases were also imagined: recent works related to this topic [19][20][21][22][23][24] show rather complex phase diagrams to represent them. In Nature, some of these ones are expected to constitute the core of neutron stars or, more generally, of compact stars. Future accelerator programs plan to explore the high densities regions of the phase diagram. Color superconductivity may be probably accessible to them [25]. To describe the color superconductivity theoretically, the QCD should be the best tool to be considered. However, at high densities, some difficulties appear in a QCD description involving the three quark colors, caused by the fermion sign problem [26]. Even if some approaches have been developed to take this problem into account [5], it constitutes a serious limitation in the study of the dense matter with the QCD.The Nambu and Jona-Lasinio (NJL) model [27,28] constitutes a reliable alternative. The main idea of this approach consists in gathering the various interactions between the quarks/antiquarks in punctual ones. It leads to consider massive gluons, described by constant terms. So, the gluon degrees of freedom are frozen in this description [29]. This model was progressively improved [29][30][31][32][33][34][35][36][37][38][39][40][41][42], in order to obtain an interesting approach to describe the quark physics at low energies. With the use of Matsubara's formalism [43], the NJL approach is fully able to work at finite temperature. The model is also usable at finite chemical potentials or finite densities. As a consequence, the NJL model appears as a serious candidate to study the color superconductivity. In fact, even if other models may also be considered, like the Dyson-Schwinger approach [44,45] or the instanton...

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