A systematic examination of 5-dimensional Kaluza-Klein theory with sources consisting of point particles or strings

Five-dimensional general relativity with sources which are five-dimensional point particles or strings was investigated as an instructive model for studying the classical Kaluza-Klein theories. The field equations and the equations of motion of a test particle were derived. Attention was paid only to those solutions which are isometric in the extra dimension. Expressions for the gravitational mass, inertial mass, electric charge and the scalar mass were derived. Next text particles and sources were treated as strings which are wound around the compact extra dimension; then a single string is a source of a field which is isometric or approximately isometric along the extra dimension. FInally some approaches which could lead to a realistic Kaluza-Klein theory are suggested