Improved dispersive analysis of the scalar form factor of the nucleon
Abstract
We present a coupled system of integral equations for the pi pi --> Nbar N and Kbar K --> Nbar N S-waves derived from Roy-Steiner equations for pion-nucleon scattering. We discuss the solution of the corresponding two-channel Muskhelishvili-Omnes problem and apply the results to a dispersive analysis of the scalar form factor of the nucleon fully including Kbar K intermediate states. In particular, we determine the corrections Deltasigma and DeltaD, which are needed for the extraction of the pion-nucleon sigma term from pi N scattering, and show that the difference DeltaD - Deltasigma=(-1.8 +/- 0.2) MeV is insensitive to the input pi N parameters.
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