Since we know the gauge theory can be emergent from local tensor product Hilbert space of quantum many body systems, such as solid state or condensed matter, etc.
How do we understand the ghosts in quantum many body systems?
Namely the Faddeev Popov ghosts in terms of many body quantum systems (for examples, from the energy band theory of lattice models, then with interactions, to have emergent gauge fields, etc)
The ghosts are needed some time to deal with the gauge fixing or to identify the unwanted negative norm states, in the 2nd quantized language.
So what do they mean in the 1st quantized language in many body quantum systems?