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In an extension of the Nambu-Jona-Lasinio model where the quarks interact with the temporal gluon field, represented by the Polyakov loop, we explore the relation between the deconfinement and chiral phase transitions. The effect of Polyakov loop dynamics on thermodynamic quantities, on the phase structure at finite temperature and baryon density and on various susceptibilities is presented. Particular emphasis is put on the behavior and properties of the fluctuations of the (approximate) order parameters and their dependence on temperature and net-quark number density. We also discuss how the phase structure of the model is influenced by the coupling of the quarks to the Polyakov loop.

We discuss the relevance of higher order cumulants of net baryon number fluctuations for the analysis of freeze-out and critical conditions in heavy ion collisions at LHC and RHIC. Using properties of O(4) scaling functions, we discuss the generic structure of these higher cumulants at vanishing baryon chemical potential and apply chiral model calculations to explore their properties at non-zero baryon chemical potential. We show that the ratios of the sixth to second and eighth to second order cumulants of the net baryon number fluctuations change rapidly in the transition region of the QCD phase diagram. Already at vanishing baryon chemical potential they deviate considerably from the predictions of the hadron resonance gas model which reproduce the second to fourth order cumulants of the net proton number fluctuations at RHIC. We point out that the sixth order cumulants of baryon number and electric charge fluctuations remain negative at the chiral transition temperature. Thus, they offer the possibility to probe the proximity of the chemical freeze-out to the crossover line.

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Using the conservation laws for charge, energy, momentum, and angular momentum, we derive hydrodynamic equations for the charge density, local temperature, and fluid velocity, as well as for the polarization tensor, starting from local equilibrium distribution functions for particles and antiparticles with spin 1 /2. The resulting set of differential equations extend the standard picture of perfect-fluid hydrodynamics with a conserved entropy current in a minimal way. This framework can be used in space-time analyses of the evolution of spin and polarization in various physical systems including high-energy nuclear collisions. We demonstrate that a stationary vortex, which exhibits vorticity-spin alignment, corresponds to a special solution of the spin-hydrodynamical equations.

We calculate the modification of the effective interaction of particles on the Fermi surface due to polarization contributions, with particular attention to spin-dependent forces. In addition to the standard spin-spin, tensor and spin-orbit forces, spin non-conserving effective interactions are induced by screening in the particle-hole channels. Furthermore, a novel long-wavelength tensor force is generated. We compute the polarization contributions to second order in the low-momentum interaction V low k and find that the medium-induced spin-orbit interaction leads to a reduction of the 3 P2 pairing gap for neutrons in the interior of neutron stars.Introduction. -Landau-Fermi liquid theory is a powerful effective theory for strongly interacting Fermi systems at low temperatures. It has been successfully applied to liquid 3 He, nuclear matter and nuclei. While the free interaction between 3 He atoms is almost stateindependent, the nuclear interaction is complicated due to large non-central spin-orbit and tensor forces, which are crucial for understanding nuclear phenomena. For investigations of matter under extreme conditions, such as nuclei with large proton or neutron excess and asymmetric nuclear matter in neutron stars, the role of non-central forces in the effective interaction must be understood.As part of a program to determine effective nuclear interactions using renormalization group methods [1], we analyze the spin-dependence of the quasiparticle interaction and the low-energy scattering amplitude in the presence of non-central forces. We focus on pure neutron matter, and as an application, we estime the modification of the 3 P 2 pairing gap in neutron star interiors due to the screening of the nucleon-nucleon interaction. This is a long-standing problem in neutron star structure, and since polarization effects suppress the S-wave gaps by a factor four [1], large effects may be expected.

We consider the thermodynamics of chiral models in the mean-field approximation and discuss the relevance of the (frequently omitted) fermion vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended version, we show that the fermion vacuum fluctuations can change the order of the phase transition in the chiral limit and strongly influence physical observables. We compute the temperature-dependent effective potential and baryon number susceptibilities in these models, with and without the vacuum term, and explore the cutoff and the pion mass dependence of the susceptibilities. Finally, in the renormalized model the divergent vacuum contribution is removed using the dimensional regularization.Comment: 9 pages, 5 figure

We study the p-wave polarization operator of the ρ-meson due to ρN interactions via the N * (1720) and ∆(1905) resonances and compute the corresponding production rate for e + e − -pairs at finite temperature and baryon density. At high baryon density we find a significant shift of the spectrum to lower invariant masses.