  We revisited gluon bremsstrahlung off a heavy quark in nuclear matter within
higher twist formalism. In this work, we demonstrate that, in addition to
transverse momentum diffusion parameter ($\hat q$), the gluon emission spectrum
for a heavy quark is quite sensitive to $\hat e$, which quantify the amount of
light-cone drag experienced by a parton. This effect leads to an additional
energy loss term for heavy-quarks. From heavy flavor suppression data in
ultra-relativistic heavy-ion collisions one can now estimate the value of this
sub-leading non-perturbative jet transport parameter ($\hat e$) from our
results.
