To resolve various outstanding issues associated with the twist four
longitudinal structure function FLτ=4​(x) we perform an analysis
based on the BJL expansion for the forward virtual photon-hadron Compton
scattering amplitude and equal (light-front) time current algebra. Using the
Fock space expansion for states and operators, we evaluate the twist four
longitudinal structure function for dressed quark and gluon targets in
perturbation theory. With the help of a new sum rule which we have derived
recently we show that the quadratic and logarithmic divergences generated in
the bare theory are related to corresponding mass shifts in old-fashioned
light-front perturbation theory. We present numerical results for the F2​ and
FL​ structure functions for the meson in two-dimensional QCD in the one pair
approximation. We discuss the relevance of our results for the problem of the
partitioning of hadron mass in QCD.Comment: 25 pages, 2 ps figures, accepted for publication in Physical Review