[en] A chirally symmetric quark model is presented which contrary to the Nambu Jona-Lasinio (NJL) model does not lead to the presence of free quarks. In the model a non-local effective interaction is used as a schematic parameterization of the quark antiquark scattering kernel. The non-locality can be interpreted as phenomenologically taking into account an infinite number of elementary scattering processes, like the sum of all multi-gluon exchange processes in the particle-particle channel. The basic Lagrangian of the interaction shares all global internal symmetries with QCD. In particular in the limit of vanishing current quark masses it is chirally symmetric. Starting from the non-local scattering kernel the solution of the Dyson-Schwinger equation and the Bethe-Salpeter equation leads to a consistent description of the dressed quark propagators with the mesonsa s quark-antiquark states. Like in the NJL-model chiral symmetry is spontaneously broken. Because of the non-locality of the interaction, however, in our model the quarks do not acquire a constant constituent mass but a four momentum dependent selfenergy. (orig.)

No abstract available

[en] We perform a study of the possible existence of hybrid stars with color superconducting quark cores using a specific hadronic model in a combination with an NJL-type quark model. It is shown that the constituent mass of the non-strange quarks in vacuum is a very important parameter that controls the beginning of the hadron-quark phase transition. At relatively small values of the mass, the first quark phase that appears is the two-flavor color superconducting (2SC) phase which, at larger densities, is replaced by the color-flavor locked (CFL) phase. At large values of the mass, on the other hand, the phase transition goes from the hadronic phase directly into the CFL phase avoiding the 2SC phase. It appears, however, that the only stable hybrid stars obtained are those with the 2SC quark cores

[en] The following topics were dealt with: Experimental results on ultrarelativistic heavy ion collisions, QCD thermodynamics, equilibration in relativistic heavy ion collisions, lattice QCD, space- time evolution and Hanbury-Brown-Twiss correlations, vector meson production, high-p_T and small-x physics. (HSI)

[en] Properties of mesons are investigated within the Nambu-Jona-Lasinio model. We include meson-loop corrections, which are generated via a systematic 1/N_c-expansion in next-to-leading order. We show that our scheme is consistent with chiral symmetry, in particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation. The numerical part focuses on the pion and the ρ-meson sector. For the latter the 1/N_c-corrections are crucial in order to include the dominant ρ→ππ-decay channel, while the leading-order approximation only contains unphysical qq-bar-decay channels. We show that a satisfactory description of the pion electromagnetic form factor can be obtained. Similarities and differences to hadronic models are discussed

[en] We investigate effects of a fixed nonzero isospin chemical potential on the μ_B-T phase diagram of strongly interacting matter using a Nambu-Jona-Lasinio-type four fermion interaction. We focus on the influence of a flavor-mixing interaction induced by instantons. We find that already for rather moderate values of the coupling strength in the flavor-mixing channel the recent findings of two separate phase transitions do not persist

No abstract available

[en] The following topics were dealt with: Nuclear many-body theory, neutron stars, supernova physics, cosmic rays, stellar evolution, nucleosynthesis key reactions. (HSI)

[en] The modification of the ρ-meson self-energy due to the coupling to in-medium pions is calculated consistently at finite baryon density and temperature, keeping the full 3-momentum dependence in a gauge invariant way. As a function of nucleon density, the ρ-meson spectral function is strongly enhanced in the invariant mass region M ≤ 650 MeV, while the maximum, i.e., the pole mass, is slightly shifted upwards. As a function of temperature, for fixed nucleon density, the imaginary part of the self-energy increases further due to Bose-enhancement. At the same time the mass shift from the real part becomes very large. As a consequence of these medium effects, the dilepton rate in the low-mass region M ≤ 650 MeV increases strongly, while the peak at M∼770 MeV disappears

[en] Full text: The quark propagator is calculated in the Nambu-Jona-Lasinio (NJL) model in a self-consistent 1/N_c expansion at next-to-leading order. The chiral quark condensate and its dependence on temperature and chemical potential is calculated directly and compared with mean field results. By using the Maximum-Entropy-Method (MEM) spectral functions are determined from the Euclidean propagators. We find a second order phase transition for the quark condensate at finite temperature whereas the critical temperature is reduced in comparison with mean field results. (author)