  Particle drifts perpendicular to the background magnetic field have been
proposed by some authors as an explanation for the very efficient perpendicular
transport of solar energetic particles (SEPs). This process, however, competes
with perpendicular diffusion caused by magnetic turbulence, which can also
disrupt the drift patterns and reduce the efficiency of drift effects. The
latter phenomenon is well known in cosmic ray studies, but not yet considered
in SEP models. Additionally, SEP models which do not include drifts, especially
for electrons, use turbulent drift reduction as a justification of this
omission, without critically evaluating or testing this assumption. This
article presents the first theoretical step for a theory of drift suppression
in SEP transport. This is done by deriving the turbulence-dependent drift
reduction function with a pitch-angle dependence, as applicable for anisotropic
particle distributions, and by investigating to what extent drifts will be
reduced in the inner heliosphere for realistic turbulence conditions and
different pitch-angle dependencies of the perpendicular diffusion coefficient.
The influence of the derived turbulent drift reduction factors on the transport
of SEPs are tested, using a state-of-the-art SEP transport code, for several
expressions of theoretically-derived perpendicular diffusion coefficients. It
is found, for realistic turbulence conditions in the inner heliosphere, that
cross-field diffusion will have the largest influence on the perpendicular
transport of SEPs, as opposed to particle drifts.
