engleski

Dynamical quark loops at low energies and in medium

We performed a research of dynamical quark loops as a basis for microscopic modelling of low-energy aspects of QuantumChromodynamics (QCD). Part of research covers the calculation of the anomalous transition of a virtual photon into three pions, within a constituent quark-meson model. We study the possibility of adding the lowest resonances, e. g. the rho and omega mesons. Research is also focused on the eta-eta' complex, which is in direct relationship with the gluonic sector of the theory. Experimental analysis of data from heavy-ion collisions at RHIC requires that the mass of the eta' particle significantly reduces at finite temperature, consequently leading to partial restoration of U(1)_A symmetry. Given result is explained by a modification of the Witten-Veneziano relation at finite temperature. General study of quark models at finite temperature and density is a third subject of this research. By calculating the equation of state it is established that covariant quark models suffer froma thermodynamic instability. Inclusion of the Polyakov loop stabilizes the system. Under certain approximations the hadron dissociation effect is discussed for the pion and the sigma particle at finite temperature. We have shown that the meson widths for dissociation into quark-antiquark pairs as functions of temperature are extremely sensitive to the particular way the quark-antiquark interaction is introduced.

Chiral symmetry; Dyson-Schwinger equations; Nambu--Jona-Lasinio model; Polyakov loop; confinement; phase diagram; equation of state; quark-gluon plasma

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