  According to a scalar theory of gravity with a preferred frame,
electromagnetism in the presence of a gravitational field implies that there is
an additional energy tensor, which might contribute to dark matter. The
expression of this tensor is determined by a mere scalar $p$, that depends on
the EM field and (for a weak field) on the Newtonian gravitational field. We
briefly recall why this tensor arises and how the EM field in a galaxy can be
calculated. The data fields that enter the PDE for the scalar field $p$
oscillate very quickly in space and time, as does the EM field. This prevents
integration of that PDE at the relevant galactic scale. Therefore, a
homogenization of that PDE has to be operated. We discuss in some detail three
possible ways of applying the homogenization theory to that PDE: time, space,
or spacetime homogenization. The second and third ways may lead to feasible,
albeit heavy calculations.
