Electromagnetic fields with symmetry

A study of the connected subgroups of the Poincare group which can be seen as invariance groups of electromagnetic fields (they will be called CEPS) and of their corresponding invariant fields is reported. It appears that the dimensions of such symmetry groups is less than or equal to six. A method of determination of fields invariant under a Poincare subgroup is proposed and applied to the characterization of all the electromagnetic fields invariant under each six- and five-dimensional CEPS. Moreover, it can be shown that each connected Poincare subgroup of dimension less than or equal to four is either a CEPS or a subgroup of a CEPS. (Auth.)