Using the $\pi N$ phase shifts and fixed-$t$ dispersion relations we have calculated (to first order in symmetry breaking) the nucleon matrix element of the current algebra "sigma" term, and found a value of about 110 MeV. This is an order of magnitude larger than the prediction of the ${(3,3^{*})}^{\oplus }(3^{*},3)$ model for chiral symmetry breaking and it indicates that $\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}\otimes \mathrm{SU}\mathrm{}\left(2\right)\mathrm{}$ breaking is comparable to SU(3) breaking.

• Received 24 December 1970

DOI:https://doi.org/10.1103/PhysRevLett.26.594