Besides Higgs Field, and not counting purely theoretical universal scalar fields such as those attributed to branes, how many universal scalar fields have been demonstrated? Please include names of such fields, if they exist.
There's just the Higgs field.
The Klein-Gordon equation is a classical scalar field that's used to teach quantisation of classical fields but there is no such physical field. In fact, Schrodinger found this equation before his eponymous equation but discarded it because of its unphysical properties.