A relativistic coupled-channel formalism for electromagnetic form factors of 2-body bound states
Elmar P. Biernat
16:00 - 18:00 Tuesday 01 June 2010 KFU Graz, Hoersaal 05.12

I present a formalism for the calculation of electromagnetic form factors of bound states consisting of two spin-1/2 constituents with equal masses. Our approach is formulated within the framework of relativistic point-form quantum mechanics. The dynamics of the
exchanged photon is explicitly taken into account by treating the
electromagnetic scattering of an electron by a bound-state as a
relativistic two-channel problem for a Bakamjian-Thomas type mass
operator. This approach guarantees Poincare invariance. By comparing the one-photon-exchange optical potential at the constituent and bound-state levels, we are able to unambiguously identify the electromagnetic form factors. Applying our formalism to spin-0 systems like, e.g. the pion, we find that in the limit of an infinitely large invariant mass, an equivalence with form-factor calculations done in front-form relativistic quantum mechanics can be established analytically. Furthermore we apply our formalism to spin-1 bound states as, e.g., vector mesons or the deuteron.