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Nucleon-nucleon bremsstrahlung: An example of the impossibility of measuring off-shell amplitudes

Harold W. Fearing
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Abstract

For nearly fifty years theoretical and experimental efforts in nucleon-nucleon bremsstrahlung (NN$γ$) have been devoted to measuring off-shell amplitudes and distinguishing among various NN potentials on the basis of their off-shell behavior. New experiments are underway, designed specifically to attain kinematics further off shell than in the past, and thus to be more sensitive to the off-shell behavior. This letter shows that, contrary to these expectations, and due to the invariance of the S-matrix under transformations of the fields, the off-shell NN amplitude is as a matter of principle an unmeasurable quantity in NN$γ$.

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Harold W. Fearing. 1998-07-03. Nucleon-nucleon bremsstrahlung: An example of the impossibility of measuring off-shell amplitudes. https://doi.org/10.1103/physrevlett.81.758

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