| Abstract: Particles with masses of order Hubble during inflation create a distinct, oscillatory signal in the squeezed limit of the CMB bispectrum. A host of models have been studied that produce non-Gaussianities in this limit, with a goal of identifying targets for near-future probes of the CMB and large-scale structure. Yet fully leveraging this program, known as ``cosmological collider" physics, as a tool for particle discovery necessitates a systematic understanding of contributing operators and their effects. In this talk, we apply a rigorous effective field theory treatment to an Abelian Higgs model, which can represent either an SM toy model or a more general U(1) gauge theory in the early universe. We identify a minimal operator basis for this model by enumerating all operators up to dimension 8, and classify their tree and one-loop behavior. In doing so, we show that the effects of tree-level operators dominate for all dimensions, establishing a visible signal for the Higgs but much lower visibility for the gauge boson. We further ascertain the signal size produced when multiple operators in the theory are turned on, demonstrating that they are on par with single-operator effects. These signals are projected to be accessible to near-future probes of large-scale structure, and we expect particular reliance on 21 cm probes to distinguish them. |