Exact Treatment of $(\pi+\pi \leftrightarrow N+\bar{N})$ Amplitude and Electromagnetic Structure of Nucleon

Abstract
The isovector part of the electromagnetic form factor of the nucleon is investigated starting from an exact treatment of the (π+π↔N+N) amplitude. It is shown that the experimental data can be reproduced very well (at least for 0 > t \gtrsim-50µ2) if the contributions from both correlating and un-correlating two-pion states are rightly included. The mass shift of the ρ-resonance is realized as a result of the coexistence of the correlated and the uncorrelated two-pion contributions. It is also shown that I = L = 1 helicity amplitude of the (π+π↔N+N) process can be determined by the present investigation of the form factors. Related problems, such as the spectral functions of the isovector form factors and the estimate of effective ρNN coupling constants, are also discussed.

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