  It has been long admitted that a consequence of the virial theorem is that
there can be no equilibrium configurations of a system of charges in
electromagnetic interaction in the absence of external forces. However, recent
results have shown that the virial theorem can not preclude the existence of
certain nontrivial equilibrium configurations. Although some of these new
results are based on an effective microscopic field theory, they are important
for a theory of ball lightning that has been developed by the authors of the
present work. Other theoretical results relative to magnetic force-free fields
with field aligned currents and self-organized filamentary structures are also
found to be relevant for this model.
