All Questions
Tagged with quantum-field-theory operators
185
questions with no upvoted or accepted answers
15
votes
0
answers
872
views
Wick theorem and OPE
I'm trying to work out in detail how the Wick theorem is used for constructing OPEs in CFT. One of the first things which bothers me is the difference in definitions of normal ordered product and ...
- 2,921
11
votes
3
answers
636
views
Why can the time-ordered exponentials be brought to the right?
Having worked through almost all calculations in section 4.2 of Peskin & Schroeder's An Introduction to QFT, I still don't get why we can get to Eq. (4.31)
\begin{equation}
\langle\Omega|\mathcal{...
- 426
6
votes
0
answers
191
views
Baryonic operators in ${\cal N}=1$ $U(N)$ SQCD in four dimensions
Seiberg's duality is usually considered as a duality for $SU(N_c)$ theories with $N_f$ flavors. In his case, the vacuum for $N_f \geq N_c$ is parameterized by mesons $M$ and baryons ${\bar B}$ and $B$....
- 647
6
votes
0
answers
182
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What is the physical interpretation of the automorphism on bounded operators induced by an S matrix?
In a QFT, the S-matrix $S$ is a unitary operator, that fixes the vacuum and commutes with the unitary operators implementing the action of the Poincare group on an appropriate Hilbert space $H$.
...
- 1,151
5
votes
0
answers
255
views
Observables and local observations in quantum field theory
I have recently taken a quantum field theory course at my university but it focused heavily on the mathematics of the theory and not the physics. So I am left with a few questions on observables and ...
- 1,747
5
votes
0
answers
251
views
QFT: Normal Ordering Interaction Hamiltonian Before Using Wick's Theorem
It has recently come to my attention, though reading the notes of a course on QFT that I've started, that there seems to be an "ambiguity" in, or at least two distinct ways of, calculating ...
- 737
5
votes
0
answers
929
views
Normal ordering in path integral of QFT
In QFT, we use normal ordering to eliminate infinity from hamiltonian. In path integral formulation of QFT though, since what we integrate over is "classical field configuration", instead of operators,...
- 327
4
votes
0
answers
107
views
Canonical commutation relation in QFT
The canonical commutation relation in QFT with say one (non-free) scalar real field $\phi$ is
$$[\phi(\vec x,t),\dot \phi(\vec y,t)]=i\hbar\delta^{(3)}(\vec x-\vec y).$$
Is this equation satisfied by ...
- 2,226
4
votes
1
answer
91
views
State-Operator Correspondence and symmetry in CFT in general dimension
Let us assume to have a QFT ($\mathcal{L}$) with translational, Lorentz, scale and conformal invariance.
I ask because we can, for example the free scalar free theory, canonically quantize the system ...
- 194
4
votes
0
answers
105
views
From particles to fields - how to reconcile these two approaches?
I was watching some lectures of the theoretical minimum program, by prof. Leonard Susskind. There he introduces the notion of fields (in the context of QFT) in a very nice and intuitive way.
Suppose ...
- 585
4
votes
0
answers
247
views
Commutation relations interacting fields
I am reading Schwartz's "Quantum field theory and the standard model". I have a question on how he derives the Feynman rules for an interacting scalar field from a Lagrangian formalism.
In ...
- 133
4
votes
0
answers
134
views
Issues of infinity with time ordering of the interaction Hamiltonian of $\phi^4$ theory
I use $\phi^4$ theory as an example here, but similar things happen to other theories as well.
In $\phi^4$ theory, we can easily use the Lagrangian here to write down the interaction Hamiltonian (in ...
- 1,335
4
votes
0
answers
188
views
What does it mean for an extended operator to possess "local excitations"?
In the context of defect conformal field theory, we consider in operator product expansions "local excitations" of the defect (see e.g. text between eq. $(1.1)$ and $(1.2)$ in the paper ...
- 1,723
4
votes
0
answers
424
views
Completeness relation and scalar product for Grassmann coherent states
I was wondering, given two fermionic canonical operators:
$$\{\hat{\chi}_{\alpha a}(x),\hat{\bar{\chi}}_{\beta b}(y)\} = \delta_{\alpha\beta}\delta_{ab}\delta^{(3)}(x-y)$$
they should have as ...
- 2,263
4
votes
0
answers
344
views
Relation of field creation operators to path integral?
Applying two field creation operators to a vacuum I get:
$$\hat{\psi}^\dagger(x)\hat{\psi}^\dagger(y)|0\rangle = (\hat{\phi}(x)\hat{\phi}(y) - s^{-1}(x-y)) |0\rangle$$
where the quantum field ...
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