Hidden gauge invariance

The role of gauge invariance is reconsidered by "deriving it without assuming it" within an autonomous approach to interactions of Standard Model particles. In this approach, the renormalizable interactions are purely constrained by quantum principles, notably the representation on a Hilbert space, which forces interactions to be "string-localized". To some surprise, most interactions fulfilling the constraints enjoy an emergent but possibly "hidden" gauge invariance (uncovered via redefinitions of quantum fields). It is exact and unbroken even in the presence of massive vector bosons. It plays a major role in proving that S-matrices are insensitive to the string-localization, and in fact coincide with S-matrices of local interactions from the gauge theory approach on indefinite state spaces. Thus, particle physics with massless and massive vector bosons can be implemented without indefinite state spaces and ghosts.