  In order to study twist-3 and transverse momentum dependent parton
distributions, we use light-front time-ordered pQCD at order $\alpha_s$ to
calculate various distribution functions for a dressed quark target. This study
enables us to investigate in detail the existing relations between twist-3 and
transverse momentum dependent parton distributions. Our calculation shows
explicitly that two versions of such relations, considered to be equivalent,
occur in the literature which need to be distinguished. Moreover, we examine
sum rules for higher twist distributions. While the Burkhardt-Cottingham sum
rule for $g_2$ is fulfilled, the corresponding sum rule for $h_2$ is violated.

High Energy Physics - Phenomenology