Speaker
Description
When particles are quantized with their physical masses in the Fock space over their unitary Wigner representations, one can find renormalizable interaction densities $L_{\rm int}(x)$ with a "tiny" but potentially disastrous flaw: they are only localized along a "string" extending from $x$ to infinity. Naively, this flaw should be ineffective because it changes local interactions only by a total derivative, but the failure of Ward identities in perturbation theory causes obstructions. The condition that all obstructions can be cancelled, strongly constrains the admissible interactions. The outcome are precisely the Standard Model interactions.
This selection criterion is "purely quantum", based on the Hilbert space axiom: classical Lagrangians and canonical quantization are not used. "Gauge symmetry" is neither invoked, nor spontaneously broken.