Faddeev–Popov ghost
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| History | 
In physics, Faddeev–Popov ghosts (also called Faddeev–Popov gauge ghosts or Faddeev–Popov ghost fields) are extraneous fields which are introduced into gauge quantum field theories to maintain the consistency of the path integral formulation. They are named after Ludvig Faddeev and Victor Popov.
A more general meaning of the word "ghost" in theoretical physics is discussed in Ghost (physics).