Quantum Field Theory (QFT) is the theoretical framework describing the quantisation of classical fields which allows a Lorentz-invariant formulation of quantum mechanics. QFT is used both in high energy physics as well as condensed matter physics and closely related to statistical field theory. Use ...
2
votes
2answers
86 views
Is there any correlation between the energy density fluctuations of two separate systems in a vacuum state?
I think the title says it all. What I am curious to find out is if there are any observable changes in the fluctuations of zero-point energy in a vacuum state system that are the consequence of ...
5
votes
2answers
318 views
Winding number in the topology of magnetic monopoles
I am reading on magnetic monopoles from a variety of sources, eg. the Jeff Harvey lectures.. It talks about something called the winding $N$, which is used to calculate the magnetic flux. I searched ...
-1
votes
1answer
170 views
What is Supersymmetry (SuSy)?
In particle physics, supersymmetry (often abbreviated SUSY) is a symmetry that relates elementary particles...etc.
what is symmetry breaking?
What is supersymmetry (SUSY)?
What is spontaneous ...
1
vote
2answers
259 views
M-theory no lagrangian?
Is there any formulated lagrangian (density) for M-theory? If not, why is there no lagrangian?
If not, is this related to many vacua existing?
Thnx.
4
votes
1answer
353 views
About $\phi^4$ model
In many books the $\phi^4$ model can produce a topological soliton called kink. Are they right? In the case of sine-Gordon model you can have a topological soliton due to you can express the ...
7
votes
3answers
657 views
Left and Right-handed fermions
Is there a simple intuitive way to understand the difference between left-handed and right-handed fermions (electrons say)?
How to experimentally distinguish between them?
4
votes
1answer
190 views
what is a kink-kink-meson vertex?
These are questions I have after reading the Rajaraman's book "Solitons and instantons". So I think you must have read the book if want to answer. And also know about quantum solitons.
Rajaraman ...
5
votes
0answers
75 views
How do you simulate a quantum gauge theory in a gauge with negative norms on a quantum computer?
How do you simulate a quantum gauge theory in a gauge with negative norms on a quantum computer? There are some gauges with negative norms. It's true that if restricted to gauge invariant states, the ...
1
vote
1answer
149 views
Exercise QFT and CFT
Consider the action functional
$S[z;t_1,t_2]=\int_{t_1}^{t^2}[g(z,\bar{z})\dot{z}\dot{\bar{z}}]^{\frac{1}{2}}dt$
with $z(t)$ a complex path with end points $z_i=z(t_i),\; i=1,2$. $g(z,\bar{z})$ is a ...
6
votes
4answers
587 views
What's the distinctions between Yang-Mills theory and QCD?
So Yang-Mills theory is a non-abelian gauge theory, and we used a lot in QCD calculation.
But what are the distinctions between Yang-Mills theory and QCD?
And distinctions between supersymmetric ...
3
votes
1answer
169 views
Non-localities in Wilsonian effective action
Why terms non-analytical dependent on momenta in the effective action (in momentum space) are non-local? How to see this directly?
0
votes
0answers
35 views
What is the spectral function in a graphene bilayer for calculating optical conductivity?
How can we use the spectral function for calculation of the optical conductivity of a graphene bilayer?
Which spectral function must we use for deriving optical conductivity? Can we change the ...
2
votes
0answers
239 views
The meaning of Goldstone boson equivalence theorem
The Goldstone boson equivalence theorem tells us that the amplitude for emission/absorption of a longitudinally polarized gauge boson is equal to the amplitude for emission/absorption of the ...
4
votes
1answer
156 views
Gauge symmetry description for $\phi^4$?
That is a follow-up to this question: Gauge symmetry is not a symmetry?
Ok, gauge symmetry is not a symmetry, but ...
... a redundancy in our description, by introducing fake degrees of freedom ...
5
votes
2answers
112 views
Is the distinction between the Poincaré group and other internal symmetry groups artificial?
For instance, given a theory and a formulation thereof in terms of a principal bundle with a Lie group $G$ as its fiber and spacetime as its base manifold, would a principle bundle with the Poincaré ...
2
votes
1answer
95 views
Imaginary pertubation to a Hamiltonian: how is it the same as rotation to imaginary time?
I am struggling with the following affirmation found in Ryder's QFT book, page 177:
instead of rotating the time axis as we have done, the ground state contribution may be isolated by adding a ...
2
votes
1answer
209 views
Spontaneous symmetry breaking and 't Hooft and Polyakov monopoles
What is spontaneous symmetry breaking from a classical point of view. Could you give some examples, using classical systems.I am studying about the 't Hooft and Polyakov magnetic monopoles solutions, ...
14
votes
3answers
793 views
Why does dilation invariance often imply proper conformal invariance?
Why does a quantum field theory invariant under dilations almost always also have to be invariant under proper conformal transformations? To show your favorite dilatation invariant theory is also ...
2
votes
0answers
208 views
How does one calculate the quantum propagator for a massless photon
So I want to calculate the quantum massless photon propagator. To do this, I write
$$
A_\mu(x) = \sum\limits_{i=1}^2 \int \frac{d^3p}{(2\pi)^3} \frac{1}{\sqrt{2\omega_p}} \left( \epsilon_\mu^i (p) ...
1
vote
2answers
325 views
Non-renormalizable corrections to GUT unification
While writing these answers: Hypercharge for U(1) in SU(2)xU(1) model and Is there a concise-but-thorough statement of the Standard Model? , it occured to me that the unification prediction for ...
0
votes
2answers
113 views
What is the importance of Vacua in Field Theory?
I understand that defining the Vacuum is important in Field Theory, why? Is this because it is the 'ground' state, before particles are added, so defines the 'background'?
I assume its not important ...
0
votes
0answers
149 views
How important are constrained Hamiltonian dynamics and BRST transformation as a formalism?
I am to study BRST transformations, for which I'm currently trying to understand constrained Hamiltonian dynamics to treat systems with singular Lagrangians. The crude recipe followed is Lagrangian -> ...
1
vote
2answers
140 views
How important are electromagnetic tidal effects in QFT? Can they be used to determine whether a particle is point-like?
I just did a back-of-the-envelope calculation, which surprised me. I calculated the difference in acceleration (due to repelling like-charges) experienced by two sides of an electron the size of the ...
7
votes
2answers
445 views
Majorana zero mode in quantum field theory
Recently, Majorana zero mode becomes very hot in condensed matter physics.
I remember there was a lot of study of fermion zero mode
in quantum field theory, where advanced math, such as index ...
4
votes
2answers
192 views
Non-relativistic spinors
Even in a non-relativistic theory Spinors can arise as irreducible representations of the rotation subgroup of the symmetries of the theory. Why do people then put so much emphasize on the role of ...
1
vote
0answers
54 views
is cosmic expansion related with IR divergencies?
This question is related to renormalization, but in the IR limit. It is assumed that unitarity does take care of IR divergencies in interacting theories like QED. But how would one interpret ...
4
votes
0answers
132 views
Why can i replace a gauge field by the current it couples to in the calculation of a greens function?
i am reading about Anomalies in QFT at the moment and there is a question that appeared on the way.
Often i find it that people are calculating the time ordered expectation value of some fields (in ...
3
votes
1answer
167 views
Propagator of the Klein-Gorden equation
Does this integral converge?
My question is related to this one:
Free particle propagation amplitude calculation
I am reading the book of Peskin and Schroesder. In the second page of their chapter ...
3
votes
2answers
335 views
When is many-body perturbation theory valid?
I'm calculating expectation values (thermal, time-independent) using many-body perturbation theory, but I'm unsure how to work out what values the parameter I'm expanding the perturbation series in ...
7
votes
3answers
492 views
The energy spectrum in quantum field theory
One of the key elements of any quantum mechanical system is the spectrum of the Hamiltonian. But what about in quantum field theory? It seems as if nobody ever discusses the spectrum of a system at ...
8
votes
0answers
139 views
gauge invariant but not gauge covariant
I'm not sure if someone's already asked this before, but I was wondering, in field theory,
when we say that a certain field is gauge invariant but not gauge covariant, what does this mean? In ...
7
votes
1answer
369 views
Correlation function which has branch cut in momentum space
When correlation function has branch cut in momentum space,
how to find correlation in coordinate space?
For example
$$ \tilde {G}(\omega) = \frac{2i}{\omega+(\omega^2-\nu^2)^{1/2}}$$
How to get the ...
1
vote
1answer
481 views
Yukawa Coupling of a Scalar $SU(2)$ Triplet to a Left-Handed Fermionic $SU(2)$ Doublet
Suppose we have a field theory with a single complex scalar field $\phi$ and a single Dirac Fermion $\psi$, both massless. Let us write $\psi _L=\frac{1}{2}(1-\gamma ^5)\psi$. Then, the Yukawa ...
3
votes
1answer
247 views
Gauge-invariant field strength term in Yang-Mills Lagrangian
I am reading the chapter of non-abelian gauge invariance from Peskin and Schroeder. Why is the term $-\frac{1}{4}(L_{\mu\nu}^i)^{2} $ gauge invariant?
4
votes
1answer
208 views
Does the vacuum energy problem of quantum field theory only occur in the Hamiltonian approach, or also in the path integral approach and in AQFT?
In a standard QFT class, you're being indoctrinated that there is the "infinite vacuum energy density problem".
(This is sometimes paraphrased as the "cosmological constant problem", which is in my ...
4
votes
0answers
130 views
Semiclassical QED and long-range interaction
I'm interested in the (very) low energy limit of quantum electrodynamics. I've seen that taking this limit does not yield Maxwell equations, but a quantum corrected non-linear version of them.
If ...
1
vote
3answers
181 views
Theory that gets rid of dark matter/energy
Is there any physics theory that either groups together gravity and dark energy/dark matter or eliminates dark energy/dark matter by modifying standard understanding of gravity or any force? If so, ...
0
votes
2answers
122 views
How is spacetime depicted in quantum field theory?
How is spacetime depicted in quantum field theory?
Is space and time completely separate, and time is just nature of law as in Newtonian mechanics?
0
votes
0answers
66 views
Does quantum field theory accept gravitational wave?
Does quantum field theory accept gravitational wave? As quantum field theory is flat spacetime theory, I wonder whether gravitational wave would be true.
Does contemporary string theory variants ...
1
vote
0answers
111 views
weird terms in W boson self energy
I calculated the correction to the self energy of the W boson due to a fermion doublet (below I have n(e) for neutrino (electron), but it could be up and down quarks or just any 4th generation ...
8
votes
3answers
491 views
Why are some solitons formed from bosonic fields fermionic?
Some topological solitons formed from bosonic fields have fermionic statistics. Why?
6
votes
3answers
161 views
Modular invariance for higher genus
As far as I understand, there are roughly 2 "common" kinds of 2D conformal field theories:
Theories that are defined only on the plane, more precisely, on any surface of vanishing genus. Such a ...
18
votes
3answers
173 views
Geometric Langlands as a partially defined topological field theory
I have heard from several physicists that the Kapustin-Witten topological twist of $N=4$ 4-dimensional Yang-Mills theory ("the Geometric Langlands twist") is not expected to give
rise to fully defined ...
16
votes
2answers
259 views
Edge theory of FQHE - Unable to produce Green's function from anticommutation relations and equation of motion?
I'm studying the edge theory of the fractional quantum Hall effect (FQHE) and I've stumbled on a peculiar contradiction concerning the bosonization procedure which I am unable to resolve. Help!
In ...
5
votes
1answer
93 views
Is there a review article that discusses the various suggestions for approaches to the Dirac spinor field?
I've come across many approaches to the Dirac spinor field over the years. A few have held more than passing interest but most of them are rather forgettable, so that I'd like to know of any reviews ...
1
vote
1answer
72 views
Can symmetry be restored in high energy scattering?
Suppose you have a field theory with a real scalar field $\phi$ and a potential term of the form $\lambda \phi^4 - \mu \phi^2$ that breaks the symmetry $\phi \to - \phi$ in the ground state. Is this ...
1
vote
1answer
146 views
Is every QFT non-local in the U.V.?
As much as I understand the renormalization group transformation and the concept of relevant/irrelevant operators, I'd say that if we push the reasoning of only looking at relevant operators when we ...
1
vote
1answer
357 views
Origin of the Higgs field
Are there any attempts in the literature at addressing the origin of the Higgs field? And, which lines of research that find it inevitable to address this question?
9
votes
3answers
437 views
Is there any quantum-gravity theory that has flat space-time and gravitons?
Many quantum-gravity theories are strongly interacting. It is not clear
if they produce the gravity as we know it at low energies. So I wonder, is there
any quantum-gravity theory that
a) is a well ...
1
vote
0answers
67 views
What is the mean field value of a scalar field with spontaneously broken symmetry in a scattering event?
Consider you have a quantum field theory that undergoes spontaneous symmetry breaking at some critical temperature. It doesn't necessarily have to be a continuous symmetry that's broken, I don't think ...
