# Questions tagged [ghosts]

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

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### Calculating the energy momentum tensor of $bc$ and $\beta\gamma$ CFT

I'm trying to calculate the energy momentum tensor of the $bc$ and $\beta\gamma$ CFT's, using a simple method of calculating the canonical expression and adding total derivatives (rather than the ...
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### Introduce Ghost Field to eliminate unphysical degrees of freedom in case of Photon Field

In wikipedia's article about ghost fields is stated the following which requires a bit more clarification: An example of the need of ghost fields is the photon, which is usually described by a four ...
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### Why does my microwave turn on other battery powered electronics?

Situation: I have a 8-10 yr old LG microwave in a small alcove built into the cabinetry of our kitchen counter. I have a pretty cheap Bomata battery powered coffee scale that I store on the countertop ...
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### What is the physical meaning of ghost field and dilaton field in general relativity?

In this paper (24)，I found a action of gravity coupling to a free scalar field. According to the literature, the scalar field is ghost or dilaton depending on the sign of kinetic terms. But in this ...
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### An explicit form for the co-BRST operator?

Take a theory with 1st class constraints $M_{\alpha}$. We gave ghosts $c^\alpha$ and their conjugates $b_\alpha$ for every constraint. The BRST operator $\Omega$ has ghost number $+1$ and has an ...
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### Ghost detection at the level of equations of motion

My question is about how to detect ghostly degrees of freedom at the level of equations of motion. It is not clear for me how does this work. Let me explain with an example: Consider the following ...
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### Faddeev-Popov ghost in the Standard-Model

When we quantize $SU(N)$ gauge theories using the path integral formalism, we must introduce Faddeev-Popov ghosts and will appears as scalar fermions coupled to our gauge bosons in the Lagrangian of ...
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### How does the BRST transformation act on ghost fields?

I understand the general idea behind constructing the BRST symmetry: take a generic gauge transformation $$$$e^\omega,$$\tag{1}$$ where $\omega$ is Lie-algebra valued, and ...
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### Conformal weights of space-time and ghosts

I'm studying the paper of Kaplunovsky https://arxiv.org/abs/hep-th/9205070 In particular in page 12 he says Hamiltonians $H$ and ̄$\bar{H}$ are totals of space-time, ghost and internal components; ...
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### The structure of the Hilbert space of 2d CFT

In many textbooks, I found similar statements that in 2d CFT (which I hope I'm not misunderstanding), one can decompose the space of states into primaries and their Virasoro descendants, or into quas-...
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### Boundary conditions for the $bc$ system

In this question, I will be referring to chapter 2 of Polchinski String Theory vol. 1. In equation (2.7.29), he states that the boundary conditions for the $bc$ system of the open string are \begin{...
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### Showing that a two-dimensional Euclidean CFT ghost action is hermitian

At the end of chapter 6 in Polchinski's String Theory book he says that the $c$ ghost is anti-hermitian. With that information, I tried to show that the action for the $bc$ system S= \...
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### Accounting for ghosts in calculation of massless closed string emission

I've been trying to do problem 5.8 from String Theory in a Nutshell by Kiritsis, which is think, also related to problem 8.10 in Polchinski. My question is this: how do we account for ghosts in the ...
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### Absence of negative-norm states in old covariant quantization of the bosonic string

This question is about the discussion about the absence of negative-norm states in the old covariant quantization of the bosonic string as presented e.g. in Becker Becker & Schwarz (BBS). Their ...
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### Free field realisation for Vertex Operators

I wanted to know if for a generic CFT (in weak coupling limit) there exists free field realisation of the vertex operators. This seems like it should exist but I want to know a generic algorithm to ...
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### Bosonization of $\beta \gamma$ system

I am studying the bosonization of the $\beta \gamma$ ghost system, also called as the symplectic boson (See for example, section 2.3 of this paper. These have OPE, \beta(z) \gamma(w) \...
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### Do Faddeev-Popov ghost contribute to vacuum polarisation?

I can imagine how one can draw a Feynman diagram for a boson self-energy with a ghost loop. My question is, shouldnt't the amplitude of that process be 0 as the ghosts are merely a mathematical tool?
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### Various Definitions of 'Ghosts'

I have seen various different definitions of a ghost field in the literature. For example, one can find many examples where ghosts are simply defined as any field with a negative sign in the kinetic ...
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