In his this book, Hatfield calls ghosts the negative states appearing in the covariant (Gupta-Bleuler) quantization prescription of the electromagnetic field (page 89). When discussing Yang-Mills fields, he comments on the Faddeev-Popov ghosts (page 356).
He mentions that the 'ghost' nomenclature is used in different ways in these two contexts: the negative states and the representations of the Faddeev-Popov determinant. It made me question if the two cannot be really connected.
Can we relate the (decoupling) Faddeev-Popov ghosts of QED in Lorenz gauge with the longitudinal and scalar photons of Gupta-Bleuler? Or maybe the only similarity between them is that they can be separated (in some sense) of the physical particles? (even if the longitudinal and scalar ones contribute to loop corrections)