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Gauge invariance, locality, and the σ2 photoabsorption sum rule

J. L. Friar* and S. Fallieros

  • Department of Physics, Brown University, Providence, Rhode Island 02912

  • *Present address: Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87545.

Phys. Rev. C 15, 365 – Published 1 January, 1977

DOI: https://doi.org/10.1103/PhysRevC.15.365

Abstract

The requirements of gauge invariance for the photoabsorption and Compton amplitudes are used to evaluate the σ2 sum rule through terms of order (1/mass). This expression is shown to equal the derivative of the dispersive part of the forward Compton amplitude with respect to the squared photon energy. In the absence of "frozen" meson degrees of freedom this is equivalent to the derivative of the entire Compton amplitude. If static exchange currents or finite nucleon charge distributions are present, the seagull terms of our model are nonlocal and modify the sum rule.

NUCLEAR REACTIONS Calculated photoabsorption cross section and Compton amplitude. Tested σ2 sum rule. Intrinsic form factors and exchange currents discussed.

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