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 mu. We measure both flavor singlet (diagonal) and non-singlet (off-diagonal) quark number susceptibilities. The diagonal susceptibility approaches the perturbative result above similar to 20T(c), but below that temperature we observe significant deviations. The results agree well with 4d lattice data down to temperatures similar to 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).