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The constraints followed from gauge invariance and analyticity are consideredfor the amplitudes of radiative transitions of composite systems when compositesystems are treated in terms of spectral integrals. We discuss gauge-invariantamplitudes for the transitions S -> gamma S and V -> gamma S with scalar S andvector V mesons being two-particle composite systems of scalar (orpseudoscalar) constituents, and we demonstrate the mechanism of cancellation offalse kinematical singularities. Furthermore, we explain how to generalize theperformed consideration for quark-antiquark systems, in particular, for thereaction phi(1020) -> gamma f0(980). Here we also consider in more detail thequark-model non-relativistic approach for this reaction.Comment: 34 pages, LaTeX, 5 figures, epsfig.st

physics of atomic nuclei

Description of composite systems in the spectral integration technique: The gauge invariance and analyticity constraints for the radiative decay amplitudes