Biomedical subjects
Publications and source records attributed to H Leutwyler.
We demonstrate that near the threshold, the pi pi scattering amplitude contains a pole with the quantum numbers of the vacuum--commonly referred to as the sigma--and determine its mass and width within small uncertainties. Our derivation does not involve models or parametrizations but relies on a straightforward calculation based on the Roy equation for the isoscalar S wave.
We show that, independently of the size of the quark condensate, chiral symmetry correlates the two S-wave pipi scattering lengths. In view of this constraint, the new precision data on K(e(4)) decay allow a remarkably accurate determination of these quantities. The result confirms the hypothesis that the quark condensate is the leading order parameter.
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