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Form factors in the 'point form' of relativistic quantum mechanics : single and two-particle currents

Abstract : Electromagnetic and Lorentz-scalar form factors are calculated for a bound system of two spin-less particles exchanging a zero-mass scalar particle. Different approaches are considered including solutions of a Bethe-Salpeter equation, a ``point form'' approach to relativistic quantum mechanics and a non-relativistic one. The comparison of the Bethe-Salpeter results, which play the role of an ``experiment'' here, with the ones obtained in ``point form'' in single-particle approximation, evidences sizable discrepancies, pointing to large contributions from two-body currents in the latter approach. These ones are constructed using two constraints: ensuring current conservation and reproducing the Born amplitude. The two-body currents so obtained are qualitatively very different from standard ones. Quantitatively, they turn out not to be sufficient to remedy all the shortcomings of the ``point form'' form factors evidenced in impulse approximation.
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Submitted on : Tuesday, August 24, 2004 - 3:18:59 PM
Last modification on : Thursday, November 19, 2020 - 12:58:39 PM

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B. Desplanques, L. Theussl. Form factors in the 'point form' of relativistic quantum mechanics : single and two-particle currents. European Physical Journal A, EDP Sciences, 2004, 21, pp.93-116. ⟨in2p3-00022163⟩

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