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Dark Photon bounds in the dark EFT

Dark photons are massive abelian gauge bosons that interact with ordinary photons via a kinetic mixing with the hypercharge field strength tensor. This theory is probed by a variety of different experiments and limits are set on a combination of the dark photon mass and kinetic mixing parameter. These limits can however be strongly modified by the presence of additional heavy degrees of freedom. Using the framework of dark effective field theory, we study how robust are the current experimental bounds when these new states are present. We focus in particular on the possible existence of a dark dipole interaction between the Standard Model leptons and the dark photon. We show that, under certain assumptions, the presence of a dark dipole modifies existing supernovæ bounds for cut-off scales up to $\mathcal{O}(10 - 100~\text{TeV})$. On the other hand, terrestrial experiments, such as LSND and E137, can probe cut-off scales up to $\mathcal{O}(3~\text{TeV})$. For the latter experiment we highlight that the bound may extend down to vanishing kinetic mixing.