  The Drell-Hearn-Gerasimov sum rule for the nucleon is investigated within a
relativistic constituent quark model formulated on the light-front. The
contribution of the N - Delta(1232) transition is explicitly evaluated using
different forms for the baryon wave functions and adopting a one-body
relativistic current for the constituent quarks. It is shown that the N -
Delta(1232) contribution to the sum rule is sharply sensitive to the
introduction of anomalous magnetic moments for the constituent quarks, at
variance with the findings of non-relativistic and relativized quark models.
The experimental value of the isovector-isovector part of the sum rule is
almost totally reproduced by the N - Delta(1232) contribution, when the values
of the quark anomalous magnetic moments are fixed by fitting the experimental
nucleon magnetic moments. Our results are almost independent of the adopted
form of the baryon wave functions and only slightly sensitive to the violation
of the angular condition caused by the use of a one-body current. The
calculated average slope of the generalized sum rule around the photon point
results to be only slightly negative at variance with recent predictions of
relativized quark models.
