I think I somehow missed the second half. Did you add it in later?
Obviously it is the child's idea of the monster that is affecting him, and that idea exists. Anyway your physics is losing me since my physics is limited to what I learned in chemistry and astronomy textbooks. I'm going to have one more unresearched, crazy, maniacal philosophical speculation?
It seems odd to ask whether an adjective has referents, but many adjectives can be made into nouns. Green is a property, and green things are a kind of thing. Conversely, to determine whether a thing exists I must have some properties by which to identify it. However to say that what exists is the thing which possesses the properties can give the impression that e.g. a boat would still exist even if it were no longer a boat, which is clearly wrong since it would mean that boats could exist in the absence of anything boat-like. I suggest that the word "exist" merely makes into an adjective the properties that define the noun. "Do boats exist?" really means "Is anything boat-like?" "Anything" is of course any instance of properties. Given that we understand the world empirically, detecting sensory properties, it questionable whether we can conceive of a thing apart from its properties.