It is shown that the physical states of a source free gauge field form pre-Hilbert spaces already on the classical level. These spaces may be closed in such a way that the determining characteristics remain. One type of free fields has a continuous mass spectrum with no mass gap. One type is massless. Dark matter may consist of (otherwise) free gauge fields. Second quantisation of free gauge fields yield G{ \aa}rding-Wightman fields identifying the massless and the massive fields as different manifestations of the same field.
Categories: math-ph math.MP