FORWARD SCATTERING-AMPLITUDE OF VIRTUAL LONGITUDINAL PHOTONS AT ZERO-ENERGY

A theorem is proved which determines the forward scattering amplitude of virtual longitudinal photons at zero energy on any hadronic target in the limit of small photon virtualities Q(2). The theorem is strict, based only on Lorenz and gauge invariance. No assumptions about the s trong interaction, other than the gap in the mass spectrum, are used. Two terms in the expansion over Q(2) are calculated. The estimation is given up to what Q(2) the elastic term can represent the whole amplit ude of longitudinal virtual photon-proton scattering.