where the summation on the right-hand side of the last equation is to be extended over the space variables only. The central symmetry of the field requires the
, to be of the form,
,
and
are functions of
where the summation on the right-hand side of the last equation is to be extended over the space variables only. The central symmetry of the field requires the
, to be of the form,
,
and
are functions of