Quark orbital angular momentum in a light-cone representation

We perform an analysis of the quark angular momentum in a light-cone representation by taking into account the effect due to the Melosh-Wigner rotation and find that there is a relativistic correction factor connecting the quark orbital angular momentum with the quark model spin distribution: L_q(x)=〈M_L(x)〉Δq_QM(x). The quark orbital angular momentum L_q(x) and the quark helicity distribution Δq(x) are connected to the quark model spin distribution Δq_QM(x) by a relation 1/2Δq(x)+L_q(x)=1/2Δq_QM(x), which means that one can decompose the quark model spin contribution Δq_QM(x) by a quark helicity term Δq(x) plus an orbital angular momentum term L_q(x). There is also a new relation connecting the quark orbital angular momentum with the measurable quark helicity distribution and transversity distribution (δq(x)): Δq(x)+L_q(x)=δq(x), from which we may have new sum rules connecting the quark orbital angular momentum with the nucleon axial and tensor charges.