Bochum 2009 – scientific programme

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HK: Fachverband Hadronen und Kerne

HK 68: Heavy Ion Collisions and QCD phases

HK 68.9: Talk

Thursday, March 19, 2009, 18:45–19:00, H-ZO 10

Functional renormalization group approach to isentropes in chiral effective theory — •eiji nakano — GSI, Darmstadt, Germany

The isentropic trajectories in the QCD phase diagram are examined in the functional renormalization group (FRG) approach, where higher momentum modes of the fluctuation fields are integrated out, thus an low-energy effective potential is generated. In particular we compute the isentropes on the T-µ plane, near the anticipated critical end point (CEP) within the quark-meson model, which belongs to the same universality class as QCD. The numerical solution of the flow equations yields the thermodynamic pressure p, the entropy density s and the net baryon density n.

Contours of constant s/n in the T-µ plane correspond to trajectories of ideal hydrodynamic evolution of the interaction region in ultra relativistic heavy-ion collisions. We have especially examined the behavior of the isentropes near the CEP and close to the crossover line of the chiral transition. We find that the strong changes in s/n in the transition region, typically found in mean-field calculations, are removed by fluctuations. Only a very smooth behavior remains, which does not exhibit focussing towards the CEP.

The isentropes near the CEP do not exhibit a universal behavior. This is supported by arguments based on the scaling functions of the 3-d Ising model, to which the QCD CEP belongs. Since s and n both remain finite at the CEP, in contrast to the divergent susceptibilities, the smooth background (non universal) contribution may dominate.