Relativistic effects on the neutron charge form factor in the constituent quark model

Abstract

The neutron charge form factor GEn(Q**2) is investigated within a constituent quark model formulated on the light-front. It is shown that, if the quark initial motion is neglected in the Melosh rotations, the Dirac neutron form factor F1n(Q**2)$receivesarelativisticcorrectionwhichcancelsexactlyagainsttheFoldyterminGEn(Q\ast \ast 2),asithasbeenrecentlyarguedbyIsgur.Moreover,atthesamelevelofapproximationtheratiooftheprotontoneutronmagneticformfactorsGMp(Q\ast \ast 2)/GMn(Q\ast \ast 2)isstillgivenbythenaiveSU(6)-symmetryexpectation,-3/2.However,itisalsoshownthatthefullMeloshrotationsbreakSU(6)symmetry,givingrisetoGEn(Q\ast \ast 2)=/0andGMp(Q\ast \ast 2)/GMn(Q\ast \ast 2)=/-3/2evenwhenaSU(6)-symmetriccanonicalwavefunctionisassumed.ItturnsoutthatrelativisticeffectsalonecannotexplainsimultaneouslytheexperimentaldataonGEn(Q\ast \ast 2)$ and GMp(Q**2)/GMn(Q**2).

Comments: final version with one minor correction and updated references; to appear in Physics Letters B