Analyticity and Regge asymptotics in virtual Compton scattering on the nucleon

We test the consistency of the data on the nucleon structure functions with analyticity and the Regge asymptotics of the virtual Compton amplitude. By solving a functional extremal problem, we derive an optimal lower bound on the maximum difference between the exact amplitude and the dominant Reggeon contribution for energies $$\nu $$ ν above a certain high value $$\nu _h(Q^2)$$ ν h ( Q 2 ) . Considering in particular the difference of the amplitudes $$T_1^\text {inel}(\nu , Q^2)$$ T 1 inel ( ν , Q 2 ) for the proton and neutron, we find that the lower bound decreases in an impressive way when $$\nu _h(Q^2)$$ ν h ( Q 2 ) is increased, and represents a very small fraction of the magnitude of the dominant Reggeon. While the method cannot rule out the hypothesis of a fixed Regge pole, the results indicate that the data on the structure function are consistent with an asymptotic behaviour given by leading Reggeon contributions. We also show that the minimum of the lower bound as a function of the subtraction constant $$S_1^\text {inel}(Q^2)$$ S 1 inel ( Q 2 ) provides a reasonable estimate of this quantity, in a frame similar, but not identical to the Reggeon dominance hypothesis.

Sum rule for the Compton amplitude and implications for the proton–neutron mass difference

The Cottingham formula expresses the leading contribution of the electromagnetic interaction to the proton-neutron mass difference as an integral over the forward Compton amplitude. Since quarks and gluons reggeize, the dispersive representation of this amplitude requires a subtraction. We assume that the asymptotic behaviour is dominated by Reggeon exchange. This leads to a sum rule that expresses the subtraction function in terms of measurable quantities. The evaluation of this sum rule leads to $$m_{\mathrm{QED}}^{p-n}=0.58\pm 0.16\,\text {MeV}$$ m QED p - n = 0.58 ± 0.16 MeV .