Evaluation of pion-nucleon sigma term in Dyson-Schwinger equation approach of QCD

We calculate the variation of the chiral condensate in medium with respect to the quark chemical potential and evaluate the pion-nucleon sigma term via the Hellmann-Feynman theorem. The variation of the chiral condensate in medium is obtained by solving the truncated Dyson-Schwinger equation for the quark propagator at finite chemical potential, with various ansatz for the quark-gluon vertex and gluon propagator. We obtain the value of the sigma term sigma(pi N) = 62(1) MeV, where the (1) represents the systematic error due to our different ansatz for the quark-gluon vertex and gluon propagator. Our result favors a relatively large value and is rather consistent with the recent data obtained by analyzing pion-nucleon scattering and pionic-atom experiments.