Twist-two matrix elements at finite and infinite volume

We present one-loop results for the forward twist-two matrix elements relevant to the unpolarized, helicity and transversity baryon structure functions, in partially-quenched (N_f = 2 and N_f = 2 + 1) heavy baryon chiral perturbation theory. The full-QCD limit can be straightforwardly obtained from these results and we also consider SU(2/2) quenched QCD. Our calculations are performed in finite volume as well as in infinite-volume. We discuss features of lattice simulations and investigate finite volume effects in detail. We find that volume effects are not negligible, typically around 5%-10% in current partially-quenched and full-QCD calculations, and are possibly larger in quenched QCD. Extensions to the off-forward matrix elements and potential difficulties that occur there are also discussed.