Pion-nucleon sigma term revisited in covariant baryon chiral perturbation theory

We study the latest N-f = 2 + 1 + 1 and N-f = 2 ETMC lattice QCD simulations of the nucleon masses and extract the pion-nucleon sigma term utilizing the Feynman-Hellmann theorem in SU(2) baryon chiral perturbation theory with the extended-on-mass-shell scheme. We find that the lattice QCD data can be described quite well already at the next-to-next-to-leading order. The overall picture remains essentially the same at the next-to-next-to-next-to-leading order. Our final result is sigma(pi N) = 50.2(1.2)(2.0) MeV, or equivalently, f(u/d)(N) = 0.0535(13)(21), where the first uncertainty is statistical and second is theoretical originated from chiral truncations, which is in agreement with that determined previously from the N-f = 2 + 1 and N-f = 2 lattice QCD data and that determined by the Cheng-Dashen theorem. In addition, we show that the inclusion of the virtual Delta(1232) does not change qualitatively our results. (c) 2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).