Stückelberg Mechanism for Ghost-Free Massive Gravity from a Hidden Gauge Sector

We propose a novel Stückelberg mechanism for generating a graviton mass through the introduction of a hidden gauge sector based on a non-unitary gauge group that contains the Lorentz subgroup, such as (A)dS. This sector undergoes spontaneous symmetry breaking via a Higgs field in the fundamental representation. We demonstrate that in the limit of an infinitely large Higgs vacuum expectation value, the dark sector decouples while leaving behind a non-vanishing graviton mass. The resulting theory is equivalent to ghost-free dGRT massive gravity. This framework realizes what we term a gauge mediation mechanism for the graviton mass. Our approach showcases how gauge theory methods can be effectively employed to formulate massive gravity and can be readily extended to engineer new classes of modified gravity theories.