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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questions
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Yang-Mills massive ghosts
Is there any procedure to add a mass to Faddeev-Popov Lagrangian density of a pure Yang-Mills theory, other than just add it from nowhere?
2
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1answer
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Physical States has ghost number 1 in String Theory
We know by no-ghost theorem (Polchinski I, section 4.4) that the physical Hilbert space have no longitudinal excitations ($X^0, X^1, b, c$). This is obvious by light-cone gauge quantization and in ...
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Questions about BRST formalism and BV formalism
This is from Pierre J. Clavier and Viet Dang Nguyen's paper Batalin-Vilkovisky formalism as a theory of integration for polyvectors.
In section 2.3, it states:
A symmetry is said to be open when it ...
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0answers
43 views
Understanding the gauge condition in light-cone gauge
When going over Cambridge String Theory Notes (page 38) I came across the following gauge conditions:
$$X^+ (t, \sigma) = x^+(t)\hspace{5mm}, \hspace{5mm} P_−(t, \sigma) = p_−(t) \tag{1} $$
which is ...
3
votes
1answer
80 views
Ghost Theory energy-momentum tensor CFT
Given the action
$$
\mathcal{S_g}=\frac{1}{2\pi}\int{d^2x\left(b\bar{\partial}c+\bar{b}{\partial}\bar{c}\right)}
$$
where $b$ and $c$ are ghosts. How can I calculate the energy-momentum tensor$$
T=...
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0answers
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Picture Number Operator in String Theory
My question concerns the ghost picture charge/picture number operator in the RNS formalism of Superstring theory.
In particular I refer to page 403 of "Basic Concepts of String Theory" by R. ...
2
votes
3answers
84 views
Gauge ghosts & unphysical states in gauge theory
I have a general question about a statement from Wikipedia about ghost states as occuring in gauge theory:
"In the terminology of quantum field theory, a ghost, ghost field, or gauge ghost is an ...
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0answers
23 views
Missing factor in Dimensionally reduced Yang Mills Ghost Field
I'm trying to calculate the ghost field in the background field gauge for the dimensionally reduced Yang Mills action in this paper. I am using the expression from Srednicki's book, chapter 78. The ...
2
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1answer
103 views
Finding ghost terms for super Yang-Mills theory in background field gauge
I want to find the ghost terms (2.16) for the action in this paper. The gauge field action is given by
$$ \begin{align}S_{A} =& i \int d\tau \Big(\frac{1}{2}A_{1}(\partial_{\tau}^2 - r^2)A_{1} + \...
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0answers
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4th polarization in the massive vector boson field propagator
We can build propagators (in this case, for massive vector fields) with at least two approaches:
(1) from canonical quantization (or exact solutions, if you like)
$$\left[[(i\partial)^2-m^2]\delta_{...
1
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1answer
55 views
Ghost exorcisms of fields?
In Mack's paper "D-independent representation of Conformal Field Theories in D dimensions via transformation to auxiliary Dual Resonance Models. Scalar amplitudes", he makes the following statement ...
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Critical dimension from the symmetries of the string action
(Related: This post and this post.)
In this thesis it is said (on page 13) that just by assuming that we have some general action with the same symmetries as the Polyakov action (Poincare invariance, ...
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Time reversal symmetry of the Faddeev-Popov determinant
I am studying the Faddeev-Popov procedure to quantize a non-Abelian gauge theory, and I got confused by the status of the time reversal symmetry. People have different definitions of the time reversal ...
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0answers
97 views
$bc$-system energy momentum tensor
I have a (maybe silly) question regarding the expression of the energy momentum tensor of the $bc$-system in equations $(2.5.11a)$ and $(2.5.11b)$ in Polchinski's String Theory, page 50. I know that ...
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votes
1answer
93 views
Supercurrent of the $bc$-$\beta\gamma$ SCFT
In Polchinksi's Sec. 10.1, the $bc$-$\beta\gamma$ SCFT is introduced with action
$$S_{BC} = \frac{1}{2\pi} \int d^2z (b \bar \partial c + \beta \bar \partial \gamma)$$
and supercurrent
$$T_F = -\...
2
votes
1answer
91 views
Longitudinal polarization of gluons in loop
I have a short question about the possible gluon polarization in loop diagrams. For external gluons, we only want the 2 transverse polarizations.
In Peskin-Schroeder it is explained that in Feynman-...
4
votes
1answer
90 views
Quantum field theory with only 3-point vertexes
Given an arbitrary quantum field theory, can I always write it in terms of another (different) quantum field theory containing only operators with 3 fields? (i.e. vertexes with 3 legs)
I guess that ...
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Ghosts use in the calculus of the scattering matrix
When you perform the calculus of $S$ matrix in, for instance, QCD maybe you need to add ghosts in external legs or internal loops. E.g.: $q\bar{q} \rightarrow gg$ needs 2 ghosts diagrams with ghosts ...
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1answer
89 views
Fermionic ghost path integral results in $\delta$ function?
This is related to a statement in pg 20 of hep-th/9408074 formula (2.39).
Suppose $$\mathcal{L}\sim\frac{i}{\lambda^{\prime}}\bar{\eta}^xg_{ij}U_x{}^i\psi^j+\cdots \tag{2.35}$$where $\bar{\eta}$ to ...
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vote
1answer
111 views
Gauge fixing while preserving supersymmetry
In supersymmetric gauge theories, the vector potential is a part of a vector supermultiplet which is represented by a real superfield $V$. Expanded out in components, the Lagrangian for such a field ...
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0answers
53 views
Do longitudinal and scalar have anything to do with Faddeev-Popov ghosts?
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 ...
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One-loop correction to triple gluon vertex in QCD
I'm trying to calculate a one loop correction to the 3 gluon vertex, which is given by a circular correction, and another that's due to the 4 gluon vertex.
However I'm unsure how the ghost fields ...
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votes
1answer
94 views
How to integrate by parts ghost fields in electrodynamics?
When applying Faddeev-Popov method to electrodynamics in the Lorenz gauge we obtain the ghost action
$$S=\int d^4xd^4y\bar\eta(x)\left(\partial^2\delta(x-y)\right)\eta(y),\tag{0}$$
where $\partial^2$ ...
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0answers
81 views
Ghost in quantum many body systems
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 ...
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1answer
290 views
Why can't Faddeev-Popov ghosts be replaced with bosons?
Faddeev-Popov ghosts are introduced in the quantization of Yang-Mills theory to absorb the Faddeev-Popov determinant into the action,
$$\det \Delta_{\text{FP}} = \int \mathcal{D} \bar{c} \mathcal{D} c ...
2
votes
1answer
128 views
Equivalence between ghosts?
Ok. I'm trying to get the terminology right about the term ghost in physics. Is there any equivalence between these terms?
Faddeev-Popov ghosts
Paul-Villars ghosts
Landau ghost
The vanishing ...
1
vote
1answer
92 views
Stuckelberg Formalism for Spin-2 - Metric Signature and Ghost Fields
Caution: This question may be trivial to experts, since I am looking at the consequence of metric conventions on the nature of fields in the calculation. My aim is to spot an error in either my ...
9
votes
2answers
632 views
Why don't high-energy experimentalists ever include Faddeev-Popov ghosts in their Feynman diagrams?
To correctly calculate scattering amplitudes in nonabelian gauge theory, one must include Feynman diagrams with internal Faddeev-Popov ghosts (fictitious fermionic scalars that only appear internally ...
2
votes
3answers
285 views
How to prove that Faddeev-Popov ghosts are unnecessary for Yang-Mills theory with axial gauge?
In the book it says that in Yang-Mills theory with axial gauge: $n_{\mu}A^{\mu}=0$ using Faddeev-Popov ghosts are needless. Does anyone know how to prove this?
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1answer
273 views
Calculating $S$-matrix in string theory
To calculate string $S$-matrix, we mainly use Faddeev-Popov gauge fixing method, as in chapter 6 of Polchinsky's book 《string theory》. But in section 6.2, 'tree level amplitude', I didn't find ...
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1answer
197 views
Anti-ghost translation invariance$.$
The Faddeev-Popov gauge-fixed Yang-Mills Lagrangian is invariant under
$$
\bar c\to\bar c+\chi
$$
for any odd constant $\chi$. What is the physical interpretation of this invariance? What does this ...
asked Aug 8 '17 at 12:23
AccidentalFourierTransform
36.5k14 gold badges88 silver badges165 bronze badges
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1answer
261 views
How do we know that renormalization doesn't change the form of the ghost action in Yang-Mills theory?
In field theory, we typically construct a Lagrangian by only specifying its (global or gauge) symmetries, then writing down all renormalizable terms that respect those symmetries with arbitrary ...
5
votes
1answer
213 views
How does Faddeev-Popov work for higher-spin fields? (or does it?)
Take for example a spin $2$ field $h_{\mu\nu}$ and some gauge-invariant Lagrangian.
Does the Faddeev-Popov trick work here? by work I mean: does it lead to a consistent and unitary theory? is the ...
asked May 24 '17 at 20:27
AccidentalFourierTransform
36.5k14 gold badges88 silver badges165 bronze badges
2
votes
0answers
294 views
Ghost Fields in Abelian and Non-Abelian gauge theories
I have some questions about ghost fields in QED and in a non Abelian gauge theory:
Does the fact that ghosts and photons are decoupled depend on the choice of the gauge-fixing function? In the Lorenz ...
2
votes
1answer
311 views
BRST Quantization of the Bosonic String: Nilpotence of BRST transformation (Polchinski)
Currently I am studying string theory and I encountered a bunch of interrelated problems in the context of BRST quantization which I can't solve for myself although I tried hard for some days.
My ...
2
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1answer
230 views
BRST Quantization of the Point Particle: Sign of Structure Functions (Polchinski)
Currently I am studying string theory and I encountered a bunch of interrelated problems in the context of BRST quantization which I can't solve for myself although I tried hard for some days.
The ...
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2answers
741 views
Why Faddeev-Popov ghost cannot exist in external line?
I was studying the path integral quantization of non-abelian gauge field. After the path integral quantization, the action becomes
$$\mathcal{L}=-\frac{1}{4}F^a_{\mu\nu}F^{a\mu\nu}-\frac{1}{2\zeta}(\...
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1answer
81 views
Beginner question on ghost system
I have read about $bc$ ant $\beta\gamma$ system. These are the fermionic and bosonic ghost system respectively. My question is
Why these systems are called ghost system?
What is the spin for these ...
2
votes
2answers
92 views
Diagonalizing Faddeev-Popov Lagrangian $U(1)$
How can we diagonalize the U(1) Faddeev-Popov Lagrangian in a consistent manner.
I can't seem to find any papers on this but I can't believe that they don't exist.
Any pointers would be greatly ...
2
votes
1answer
259 views
$U(1)$ Faddeev-Popov formalism
What is the correct series expansion for the $U(1)$ Faddeev-Popov ghosts?
I know that the $U(1)$ ghosts are only a phase such that they can be neglected in most cases but it turns out that this is ...
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votes
3answers
2k views
Why do negative norm states break unitarity?
I often hear my teachers say that the negative norm states break unitarity. And I can also read this elsewhere, such as at this place
In this gauge the relation between unitarity and gauge ...
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0answers
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Can a vector boson carry cosmic acceleration?
Clifton, Ferreira, Padilla and Skordis discuss ghosts arising from dark energy:
To get cosmic acceleration we need an additional repulsive force to
act between massive objects at large distances. ...
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2answers
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How do Faddeev-Popov (FP) ghosts help path integrals?
How does the inclusion of Faddeev-Popov ghosts in a path integral help to fix the problem of over counting due to gauge symmetries?
So, after exponentiating the determinant for the inclusion of ...
2
votes
1answer
493 views
Gauge anomalies ruin the unitarity - the explanation involving ghosts
An outline
As is known, the presence of gauge anomalies leads to breakdown of the unitarity of the gauge theory.
One way to understand this is to involve the BRST quantization of the gauge field ...
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1answer
179 views
String Theory, Ghost SCFTs
In the section on free SCFTs in chapter 10, in equation (10.1.19) of Polchinski's volume 2, it isn't clear to me how he writes down the fermionic stress tensor. Shouldn't that correspond to a world ...
2
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0answers
197 views
Anticommutator BRST charge and $c$-ghost mode
My goal is to compute the anticommutator $\{Q_B, c_m\}$ where $Q_B$ is the BRST charge in string theory and $c_m$ is the $m$th mode of the $c$ ghost field
$$
c(z) = \sum_m \frac{c_m}{z^{m-1}}
$$
(...
3
votes
1answer
406 views
Why do Faddeev-Popov ghost anti-commute?
I'm trying to understand why the Faddeev-Popov ghost that appear in the quantization of non-abelian gauge theories are anti-commuting fields.
I've seen a number of books (chapters), lecture notes and ...
2
votes
0answers
80 views
Determinants in path integrals in gauge theories and geometry
I know that in the formalism of path integral it is easy to show how determinants, corresponding to gauge fixing condition and FP ghosts, appear. But there is strict explanation of these determinants ...
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1answer
1k views
What is the relationship between BRST symmetry and gauge symmetry?
As far as i know the BRST symmetry is an infinitesimal (and expanded) version of gauge symmetry. Recently I read the following:
"when QFT was reformulated in fiber bundle language for application to ...
3
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1answer
472 views
BRST quantization (Green, Schwarz, Witten)
In Green, Schwarz, Witten Volume 1, section 3.2, BRST quantization is introduced in a general way. A Lie algebra $G$ is defined with elements
$$ [K_i,K_j] = f_{ij}{}^k K_k \tag{3.2.1}$$
where $f_{ij}{}...
