The pion-nucleon sigma term from Lattice QCD

Abstract

We summarize recent evidence, both from lattice QCD and chiral perturbation theory, that suggests that larger-than-expected excited-state contamination could be the reason for the tension between phenomenological determinations and previous direct lattice-QCD calculations of the pion--nucleon sigma term ${\sigma }_{\pi N}$. In addition, we extend the $\chi$PT analysis by calculating the corrections due to including the $\Delta (1232)$ resonance as an explicit degree of freedom. This correction is found to be small, thereby corroborating the excited-state effects found in the $\Delta$-less calculation and the result for ${\sigma }_{\pi N}$.

Comments: Includes new analysis of $\Delta$ corrections to excited-state contamination. Contribution to the 10th International Workshop on Chiral Dynamics