Gauging Open EFTs from the top down (opens in new tab)

arXiv:2512.17089v2 Announce Type: cross Abstract: We present explicit top-down calculations of Open EFTs for gauged degrees of freedom with a focus on the effects of gauge fixing. Starting from the in-in contour with two copies of the action, we integrate out the charged matter in various $U(1)$ gauge theories to obtain the Feynman-Vernon influence functional for the photon, or, in the case of symmetry breaking, for the photon and St\"uckelberg fields. The influence functional is defined thr...