Linear Chemical Potential Dependence of Two-Quark Condensate

By differentiating the inverse dressed quark propagator at finite chemical potential μ with respect to μ, the linear response of the dressed quark propagator to the chemical potential can be obtained. From this weextract a model-independent formula for the linear chemical potential dependence of the in-medium two-quarkcondensate and show by two independent methods (explicit calculation and Lorentz covariance arguments) that thefirst-order contribution in μ to the in-medium two-quark condensate vanishes identically. Therefore if one wants tostudy the in-medium two-quark condensate one should expand to at least the second order in the chemicalpotential μ.