Chiral Symmetry and the Nucleon Spin Structure Functions

We carry out a systematic investigation of twist-two spin dependent structure functions of the nucleon within the framework of the chiral quark soliton model (CQSM) by paying special attention to the role of chiral symmetry of QCD. The importance of chiral symmetry is illustrated through the good reproduction of the recent SLAC data for the neutron spin structure function $g_1^n (x,Q^2)$. We also observe substantial difference between the predictions of the longitudinally polarized distribution functions and those of the transversity distribution functions. That the chiral symmetry may be responsible for this difference is seen in the isospin dependence of the corresponding first moments, i.e. the axial and tensor charges. The CQSM predicts $g_A^{(0)} / g_A^{(3)} \simeq 0.25$ for the ratio of the isoscalar to isovector axial charges, while $g_T^{(0)} / g_T^{(3)} \simeq 0.46$ for the ratio of the isoscalar to isovector tensor charges, which should be compared with the prediction $g_A^{(0)} / g_A^{(3)} = g_T^{(0)} / g_T^{(3)} = 3 / 5$ of the constituent quark model or of the naive MIT bag model without proper account of chiral symmetry. Another prominent prediction of the CQSM is the opposite polarization of the $\bar{u}$ and $\bar{d}$ antiquarks, thereby indicating the SU(2) asymmetric sea quark (spin) polarization in the nucleon.