RELATIVISTIC EFFECTS, QCD MIXING ANGLES AND N-]N-GAMMA AND DELTA-]N-GAMMA TRANSITION FORM-FACTORS

It is shown that relativistic effects, considered in the framework of a relativistic quark model constructed in infinite momentum frame, improve the agreement between theory and experiment for DELTA --> N gamma transition. They enlarge the magnitudes of the amplitudes A1/2P and A3/2P, and suppress with increasing Q2 the magnetic form factor of DELTA --> N gamma transition in comparison with proton magnetic form factor. The additional inclusion of small QCD-inspired mixings of multiplet [56',0+] into the N and the DELTA further improves the agreement with experiment for this form factor and permits description of its Q2-dependence at Q2 < 3 GeV2. Predominantly due to the relativistic effects, non-zero values for electric and Coulombic form factors of DELTA --> N gamma transition are obtained. It is predicted that the electric form factor is positive at Q2 < 0.4 GeV2 and changes its sign with increasing Q2, so the magnitude of helicity asymmetry should be lower than 0.5 at Q2 > 0.4 GeV2.