Abstract:
We compute the structure function $g_2$ for a gluon target in perturbative QCD at order $\as$. We show that its first moment vanishes, as predicted by the Burkhardt-Cottingham sum rule.

Abstract:
In the small $Q^2$ region, the sum rule for the polarized structure function $g_2$ corresponding to the moment at $n=0$ is derived. This sum rule shows that there is a tight connection among the resonances,the elastic and the continuum in the $g_2$. Further, the Born term contribution in this sum rule is proportional to $Q^2$ and very small compared with that in the corresponding sum rule for the polarized structure function $g_1$. However, the Born term contribution divided by $Q^2/2$ which also appears in the Schwinger sum rule for the $g_2$ corresponding to the moment at $n=1$ has a very similar behavior with that in the sum rule for the $g_1$ corresponding to the moment at $n=0$.

Abstract:
In the small $Q^2$ region, the sum rule for the polarized structure function $g_2$ corresponding to the moment at $n=0$ is derived. This sum rule shows that there is a tight connection among the resonances,the elastic and the continuum in the $g_2$. Further, the Born term contribution in this sum rule is proportional to $Q^2$ and very small compared with that in the corresponding sum rule for the polarized structure function $g_1$. However, the Born term contribution divided by $Q^2/2$ which also appears in the Schwinger sum rule for the $g_2$ corresponding to the moment at $n=1$ has a very similar behavior with that in the sum rule for the $g_1$ corresponding to the moment at $n=0$.

Abstract:
A recent lattice calculation of the spin-dependent structure function g_2 is revisited. It has been recognized that the twist-three operator, which gives rise to d_2, mixes non-perturbatively with operators of lower dimensions under renormalization. This changes the results substantially.

Abstract:
The small-x behavior of the singlet contributions to the polarized structure function g_2(x,Q^2) is calculated in the double-logarithmic approximation of perturbative QCD. The dominant contribution is due to the gluons which, in contrast to the unpolarized case, mix with the fermions also in the small-x domain. We find a power-like growth in 1/x in the odd-signature parts of the amplitude with the same power as in the singlet function g_1(x,Q^2) at x<< 1.

Abstract:
The nonsinglet spin dependent structure function $g_2(x,Q^2)$ is studied at small x within the double logarithmic approximation of perturbative QCD. Both positive and negative signature contributions are considered, and we find a power-like growth in $1/x$. We discuss how our result fits into the Wandzura-Wilczek relation.

Abstract:
Quark mass effects are clarified in the parton model approach to the transversely polarized nucleon structure function. The special propagator technique is employed to obtain manifestly gauge invariant results and extract the buried short-distance contributions inside the soft part after momentum factorization in the collinear expansion approach. A generalized massive special propagator for a massive quark is constructed. We identify the corresponding matrix elements of the transversely polarized structure function in deep inelastic scatterings by the massive special propagator technique.

Abstract:
we determine the polarized quark distributions and structure functions for nuclear media such as li7 and al27 by using a phenomenological model known as thermodynamical bag model. the evaluation of nuclear medium modifications to single nucleon structure function discusses the predictions of the polarized emc effect. the deviation of polarized emc from unpolarized case shows quenching of polarized quark distributions and proves the significance of this study as adding the spin observables will explore more about medium modification of nuclear structure and the nature of the strong interaction.

Abstract:
The contribution of the $G_2$ structure function to polarized deep inelastic scattering is slightly redefined in order to avoid kinematical zeros. Its strong $Q^2$-dependence implied by the Burkhardt-Cottingham (BC) sum rule naturally explains the sign change of the generalized Gerasimov-Drell-Hearn (GDH) sum rule. The status of the BC sum rule and implications for other spin processes are discussed.

Abstract:
The effect of magnetic field on the structure properties of hot spin polarized strange quark stars has been investigated. For this purpose, we use the MIT bag model with a density dependent bag constant to calculate the thermodynamic properties of spin polarized strange quark matter such as energy and equation of state. We see that the energy and equation of state of strange quark matter changes significantly in a strong magnetic field. Finally, using our equation of state, we compute the structure of spin polarized strange quark star at different temperatures and magnetic fields.