High-Precision Determination of the Pion-NucleonσTerm from Roy-Steiner Equations

We present a determination of the pion-nucleon (πN) σ term σ_πN based on the Cheng-Dashen low-energy theorem (LET), taking advantage of the recent high-precision data from pionic atoms to pin down the πN scattering lengths as well as of constraints from analyticity, unitarity, and crossing symmetry in the form of Roy-Steiner equations to perform the extrapolation to the Cheng-Dashen point in a reliable manner. With isospin-violating corrections included both in the scattering lengths and the LET, we obtain ${{σ}}_{{π}N}=(59.1±{}1.9±{}3.0) MeV=(59.1±{}3.5) MeV$, where the first error refers to uncertainties in the ${π}N$ amplitude and the second to the LET. Consequences for the scalar nucleon couplings relevant for the direct detection of dark matter are discussed.