General Spin-1 Dynamics During Inflation: Microcausality Constraints and Cosmological Collider Signals
The research constructs a general spin-1 field theory on inflation using a Boostless Proca model constrained by microcausality. It shows that while leading-order bispectrum signals are indistinguishable from standard theories, the trispectrum provides a unique, model-independent signature capable of measuring all five free parameters of the new theory.