General QCD parametrization of the charge radii of p , n and Δ+

Using the general parametrization method we discuss the relation: r2(p)−r2(n)=r2(Δ+) between the charge radii of p , n and Δ+ derived in a recent quark model calculation of Buchmann, Hernandez and Faessler [Phys. Rev. C 55 (1997) 448]. We show that the above relationship is obtained by the general parametrization if one excludes three index and closed loop terms, which are indeed absent in the model quoted above; this checks the correctness of the calculation of Buchmann et al. on this point. However in QCD, where three index terms exist, arising e.g. from two gluon exchanges between three different quark lines, the above relationship is modified; an estimate indicates that this modification should be between 10% and 20%.