Susceptibilities and screening masses in two flavor QCD

We study QCD with two flavors of dynamical staggered quarks at finite temperature, with a bare sea quark mass of about 17 MeV. We report investigations of baryon, isospin, charge and strangeness susceptibilities, as well as screening masses obtained from correlators of local and one-link separated meson operators. These are studied as functions of the valence quark mass at several temperatures. Our results for susceptibilities deviate significantly from ideal gas values, and even more from the weak coupling series. We also report the first measurement of off-diagonal quark number susceptibilities below the transition temperature $T_c,$ where they are the main contribution to charge fluctuations. We present evidence for a close connection between the susceptibilities and the screening masses.