Topological Axi-Higgs Dynamics in Anomalous $U(1)$ Portals

Abstract

We develop an effective axi-Higgs model with one Standard Model Higgs doublet, one charged hidden Higgs and an anomalous Abelian vector portal. Extending previous Higgs--Stueckelberg constructions, we derive the Stueckelberg kinetic term by decoupling a heavy scalar radial mode and identify the gauge-invariant physical pseudoscalar from the mixing of the surviving scalar phases. A single instanton-motivated periodic interaction determines the axi-Higgs mass, its couplings to the hidden radial excitation and the sine-Gordon kink in the fixed-radial-field limit. We construct the anomaly-canceling gauge completion, using an Abelian A--B example to introduce the mechanism before its non-Abelian hidden-sector realization. We examine the relation between the periodic potential, the hidden gauge dynamics and the theta-vacuum energy, identifying the invariant angle through the anomalous Yukawa phase rotation. The vector portal gives a coherent elastic nuclear-scattering cross section and permits additional axi-Higgs emission, whose diagrams and kinematic threshold we determine. Numerical examples illustrate the mass and interaction scales, and we investigate conditional thermal relic abundances and their cosmological implications.