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Ghosts are unphysical states that arise when quantizing gauge theories. Do not use this tag for 'ghosts' in the paranormal sense.

4 votes

Diagonalizing Faddeev-Popov Lagrangian $U(1)$

There's one serious flaw in your entire strategy. Since $\overline{c},\,c$ are fermions, they are Grassmann-number-valued. Thus any complex numbers $w,\,z$ satisfy $(w\overline{c}+zc)^2=0$. You theref …
J.G.'s user avatar
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2 votes

How does Faddeev-Popov work for higher-spin fields? (or does it?)

Let's consider perturbative quantum gravity as an example, with full metric $g_{\mu\nu}^f=g_{\mu\nu}+\kappa h_{\mu\nu}$. The Nakanishi-Lautrup auxiliary field and Faddeev-Popov ghost and antighost are …
J.G.'s user avatar
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2 votes

Anti-ghost translation invariance$.$

Like any continuous symmetry, it represents a conservation law. The symmetry is manifest in the Lagrangian density term $-i\partial_\mu\bar{c}D^\mu c$, where $\bar{c}$ is cyclic. But if we add a total …
J.G.'s user avatar
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0 votes

How to prove that Faddeev-Popov ghosts are unnecessary for Yang-Mills theory with axial gauge?

It's for the same reason they're unnecessary in Abelian theories. The FP-ghost term multiplies $e^{iS}$ by $\exp-\int d^4 x \bar{c}\partial_\mu D^\mu c=\det \partial_\mu D^\mu$, a determinant that can …
J.G.'s user avatar
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2 votes

Equivalence between ghosts?

Faddeev-Popov ghosts can't be observed as particles because they violate the spin-statistics tension; Pauli-Villars ghosts are negative-norm states; the Landau pole tells you your theory must give way … to another at high energies; Goldstone ghosts represent an unphysical artefact of gauge fixing. …
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4 votes
Accepted

$U(1)$ Faddeev-Popov formalism

As discussed in Kugo and Ojima 1979, "ghost is Hermitian, anti-ghost is anti-Hermitian" is just a convention, another being that both fields are Hermitian, which results in a factor of $i$ in the FP-g …
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