The diagonal and off-diagonal quark number susceptibility of high temperature and finite density QCD
We study the quark number susceptibility of the hot quark-gluon plasma at zero and non-zero quark number density, using lattice Monte Carlo simulations of an effective theory of QCD, electrostatic QCD (EQCD). Analytic continuation is used to obtain results at non-zero quark chemical potential. We measure both flavor singlet (diagonal) and non-singlet (off-diagonal) quark number susceptibilities. The diagonal susceptibility approaches the perturbative result above 20T_c, but below that temperature we observe significant deviations. The results agree well with 4d lattice data down to temperatures 2T_c. The off-diagonal susceptibility is more prone to statistical and systematic errors, but the results are consistent with perturbation theory already at 10T_c.