Evaluation of current-algebra relations for electroproduction amplitudes

Abstract

We evaluate current algebra relations connecting electroproduction amplitudes and nucleon form factors for momentum transfers up to 100 fm −2, using electroproduction amplitudes calculated from dispersion theory. Two methods are considered: First, the fixed mass extrapolation method of Adler and Gilman, and second the method of Fubini and Furlan, in which the electroproduction amplitudes are evaluated at the Breit-frame threshold. The Adler-Gilman extrapolation method is found to work quite well up to high values of λ 2, especially in case of the sum rules for F 2 V( λ 2). The relation for A 6 (−) gives some indication that the λ 2 dependence of the axial form factor is approximately given by G A( λ 2)/ G A(o)= F 1 V( λ 2). In contrast, the evaluation of the Fubini-Furlan relations turns out to be quite difficult. Information on the electroproduction amplitudes which goes beyond the Born approximation can only be obtained by a detailed knowledge of the correction integrals. Some predictions obtained by Furlan, Paver and Verzegnassi are different from what is expected from usual dispersion theory.