Criticallinesandpoints.ppt

Critical lines and points  in the QCD phase diagram Understanding the phase diagram Phase diagram for ms mu,d Order parameters Nuclear matter and quark matter are separated from other phases by true critical lines Different realizations of global symmetries Quark matter: SSB of baryon number B Nuclear matter: SSB of combination of B and isospin I3 neutron-neutron condensate “minimal” phase diagram for equal nonzero quark masses Endpoint of critical line ? How to find out ? Methods Lattice : You have to wait until chiral limit is properly implemented ! Models : Quark meson models cannot work Higgs picture of QCD ? Experiment : Has Tc been measured ? Indications for first order transition ! Lattice Lattice results e.g. Karsch,Laermann,Peikert Critical temperature in chiral limit : Nf = 3 : Tc = ( 154 ± 8 ) MeV Nf = 2 : Tc = ( 173 ± 8 ) MeV Chiral symmetry restoration and deconfinement at same Tc pressure realistic QCD precise lattice results not yet available for first order transition vs. crossover also uncertainties in determination of critical temperature ( chiral limit …) extension to nonvanishing baryon number only for QCD with relatively heavy quarks Models Analytical description of  phase transition Needs model that can account simultaneously for the correct degrees of freedom below and above the transition temperature. Partial aspects can be described by more limited models, e.g. chiral properties at small momenta. Chiral quark meson model Limitation to chiral behavior Small up and down quark mass - large strange quark mass Particularly useful for critical behavior of second order phase transition or near endpoints of critical lines (see N. Tetradis for possible QCD-endpoint ) Quark descriptions ( NJL-model ) fail to descr