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 ...

learn more… | top users | synonyms (1)

1
vote
0answers
19 views

why in such a fundamental theory as QFT we learn only two computations?! (cross sections, decay rates)

when i learned Newtonian mechanics i found a wast variety of computations that i could do and that was so interesting. and it was so when i learned Maxwell theory. when i started learning QFT i hoped ...
0
votes
0answers
9 views

Is the time ordering in Dyson series either 1 or -1?

Because I think to make it a unitary operator, the norm of the unitary operator should be one. But I did not see any claim about the value of time ordering in Dyson series.
-1
votes
0answers
26 views

Why we have to sum in all final states of hadrons

Correct if i am wrong. In deep inelastic scattering have to sum in all final sates hadrons because we do not want to detect the hadrons. all we want to detect is the electron. Am i right?
3
votes
1answer
37 views

deriving Bio-Savart law in QFT

It's so important and meaningful that a new theory of physics contains main equations and results of previous related ones. Maxwell theory and QFT both have explanations on electromagnetic phenomenon ...
0
votes
0answers
24 views

Heisenberg uncertainity principle is valid in the case of QFT? [duplicate]

The Heisenberg uncertainty principle is valid (or taken into account) in the case of QFT?
1
vote
0answers
13 views

Can charged scalar have non zero vev?

In Higgs-Kibble mechanism, if we consider a SU[2]_L doublet of complex scalar fields, then one of them is charged and the other neutral. Why does the neutral field acquire vev and not the charged one? ...
0
votes
0answers
25 views

How do (special) groups such as U(1) and SU(2) do represent the electromagnetic and weak forces? [on hold]

I don't see how groups, such as the circle group somehow representing electromagnetism, represent the fundamental forces. Where is this connection between maths and theoretical physics? Also, as a ...
-3
votes
1answer
61 views

Is there one wavefunction per field? [on hold]

Is the big picture of quantum field theory that: There are fields (EM, electron, Higgs, gravity, etc.) A field can be described by a wavefunction indicating the probability density of 1 or more ...
0
votes
0answers
19 views

What is the most essential theoritical constrains should be imposed on arbitrary potential's parameters?

I'm little confused about the unitarity and perturbativity constrains which imposed on a potential's parameters, like 2HD potential. Look for example: [arXiv:1507.03618v3 [hep-ph]] First, I'd like to ...
7
votes
2answers
50 views

bare Phonon and Symmetry Breaking

In condensed matter physics, the phonon is considered as a quasiparticle which is a result of the quantization of lattice vibrations. In many textbooks on solid state physics, it can be done if we ...
2
votes
0answers
41 views

Higgs mechanism in quantum GLSM

My question is regarding the following Gauged Linear Sigma Model (GLSM) in two dimensions. $$\tag{1} S=\int d^2x\Big(-D_{\mu}\overline{\phi} D^{\mu}\phi +\frac{D^2}{2e'^2} +D(|\phi|^2-r)\Big).$$ ...
0
votes
0answers
67 views

QFT Weinberg scattering thoery [on hold]

I have a question about beginning of chapter 3 (scattering) of QFT.vol.1 by Weinberg I think (am I wrong?) $\Psi_\alpha$ means a collection of particles each with a definite $p^\mu$ specially $p^0$ ...
1
vote
0answers
42 views

Sudakov double logarithm

I have calculated a few NLO corrections in QED and in the final result the Sudakov double logarithms have always canceled. So I thought that they have no physical meaning. On the other hand I have ...
3
votes
0answers
31 views

Non-abelian current commutators

There many articles, in which non-abelian current commutators are computed. The general result is that quantum corrections lead to additional term in commutator $$[J^a_\mu (x), J^b_\nu (y)] \delta ...
4
votes
1answer
90 views

Photons are self-conjugate but neutrinos may or may not: why is that?

Caution: This may be a very naive question but I find it confusing. Moreover, I believe this question is based on potential misconception. I would like it to be clarified. Although the neutrinos are ...
-1
votes
0answers
48 views

Connexion of S matrix and path integral [on hold]

I have been studing the path integral formalism but all I am finding is how to calculate time ordering product. How can we connect it with the S-matrix in the canonical formalism?
-3
votes
0answers
29 views

Do the broken symmetry functions of a Mexican hat potential form a smooth function throughout space?

When the symmetry of a Mexican hat potential is spontaneously broken, the new zero potential comes to lie on one of the points on the rim of the hat (the collections of potentials with zero as value). ...
3
votes
1answer
57 views

Vacuum expectation value in presence of a source

If a vacuum is translationally invariant i.e., $P^\mu|0\rangle=0$ or $e^{(\pm ip\cdot x)}|0\rangle=0$, we can express the the vacuum expectation value of a field as $\langle 0|\phi(x)|0\rangle$ as ...
3
votes
1answer
26 views

About series expansion of effective potential and its justification

The books on quantum field theory often uses an expansion of the effective action $\Gamma[\phi_c]$ in terms of $\phi_{cl}$ and its derivatives given by $$ \Gamma[\phi_c]=\int ...
0
votes
0answers
33 views

Klein Gordon, Dirac, Proca [closed]

How do we know these equations : Klein-Gordon, Dirac, Proca is for spin 0, spin 1/2 , spin 1? How did people find Klein Gordon doesn't work for spin 1/2?
3
votes
1answer
49 views

Physical interpretations of the generating functions $Z[J]$ and $W[J]$ (or $E[J]$)

In quantum field theory, the generator of all Green's functions $Z[J]$ and that of the connected Green's functions $E[J]$ are related as $$Z[J]=\exp[-iE[J]]=\int D\phi\exp[i\int ...
3
votes
1answer
55 views

Propagator from Path integral

In class we have proved something like: $$ \frac{\partial^2 Z(J,\bar{J})}{\partial J(x) \partial \bar{J}(x')}\frac{1}{Z}|_{J=\bar{J}=0}=\Delta(x-x').$$ That by introducing source terms to path ...
0
votes
0answers
18 views

Hankel transformation of Yukawa potential [closed]

This is a Hankel transformation problem that is used to do the 2-d Fourier transformation of Yukawa potential. We already know that $H_0(\frac{1}{z^2 + r^2}) = K_0(kz)$. Then what should be the right ...
0
votes
1answer
40 views

Yukawa Potential in non-relativistic limit

In Peskin's book "An Introduction to Quantum Field Theory", on page 121 (section 4.7) , it tries to recover the Yukawa Potential in the nonrelativistic limit, but there's a simplification that I don't ...
0
votes
1answer
46 views
3
votes
2answers
95 views

What happens when two wavefunctions meet?

Apologies for the over-broad question(s), but I'm having a hard time finding out where to look to answer these myself: If a particle is a wavefunction describing a probability amplitude distributed ...
2
votes
0answers
52 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 ...
2
votes
1answer
65 views

Anomaly, Ward identity [closed]

While studying notes on anomaly by Adel Bilal (http://arxiv.org/abs/0802.0634), I stuck in a calculation. Here it goes as follows: The three-current correlator in perturbation theory as a one-loop ...
2
votes
1answer
100 views

Confusion in understanding of quantum fluctuations and vacuum energy

I'm having a bit of trouble understanding what exactly is meant by a quantum fluctuation of a quantum field and its relation to the vacuum energy attributed to such a field. Is the point, that due ...
6
votes
1answer
287 views

What is meant by the term “value” of a scalar quantum field?

During the slow roll of a scalar field, the scalar field is changing its value over time. But what is meant by the term "value" of a scalar field? Since the scalar field is quantized, I don't ...
-1
votes
0answers
48 views

Manipulating tensors in relativistic quantum mechanics

I was doing a problem that involved showing a Heisenberg equation of motion was consistent with the Dirac equation. The question involved a lot of algebra which was generally fine but something done ...
0
votes
0answers
27 views

What's the mathematical relation between 1PI Green's function and standard Green's function (in momentum space)? [closed]

I need the mathematical relation between 1PI Green's function and standard Green's function (in momentum space) to derive the ward identity for 1PI Green's function for scale transformation(ref-broken ...
3
votes
0answers
76 views

Simple, physical explanations for Hadamard behaviour of two-point functions

The two-point function of local quantum fields on a curved spacetime exhibits a singularity of a very particular form, known as Hadamard form, for null separated points $(x,y)$ (including the ...
0
votes
0answers
29 views

Quartic interactions of a complex scalar field

For a quartic self-interaction of a complex scalar field (matrix), one can write the terms: $aTr((\phi^*\phi)^2)$ and $bTr(\phi^*\phi)^2$ ; the trace and the "double" trace term, with two different ...
3
votes
1answer
30 views

Reaching equilibrium in a blackbody and light-matter interaction

Suppose we have a metallic cavity maintained at a fixed temperature. Suppose we start with any distribution of radiation that is not in equilibrium with the container. Gradually, when the equilibrium ...
14
votes
2answers
892 views

Rest mass of phonon: is this concept definable?

Phonons are obtaied by non-relativistic quantization of the lattice vibration. The dispersion relation is given by $\omega=c_s k$ where $c_s$ is the velocity of sound. What can we say about the mass ...
0
votes
1answer
34 views

Inner product of standard-momentum one-particle states in Weinberg

My question has essentially already been addressed in Questions concerning some parts of the section on one-particle states in Weinberg's first volume on QFT (third question), but unfortunately ...
5
votes
0answers
173 views

From Quantum Mechanics to Quantum field theory to String theory?

Today during a very "unique" study session, I might have internalized why Quantum mechanics was not enough, and Quantum field theory makes sense. It seems the reasons are that When a potential is ...
-3
votes
1answer
58 views

With the descent of Newtonian mechanics is Newton's third law still valid?

Or more specifically, with the standard model, quantum theory and other advances in physics, all those experiments in CERN and other accelerators, was there any occurrence where this law was violated? ...
3
votes
0answers
45 views

LSZ formula in spontaneously broken gauge symmetry

The LSZ formula connects scattering amplitudes with the pole structure of correlation functions. I've only seen the derivation for $\phi^4$, and the poles where then simply the dressed propagators of ...
5
votes
1answer
103 views

Physical interpretation of the retarded vs. Feynman propagators?

We calculate the real-space propagator $\Delta(x)$ for a free real scalar field $\varphi(x)$ with mass $m$ by performing the Fourier transform (using sign convention +---) $$\Delta(x) = \int ...
1
vote
0answers
72 views

“Constant Fermion”

I was talking to a professor in my institution which works in Lorentz Violation of various QF theories. While we talk about a SUSY lagrangian, I asked him if we could have a fermion acquiring VEV and ...
-1
votes
0answers
51 views

Virtual Photons [duplicate]

In QFT formalism of Feynman diagrams, all propagators must be off-shell otherwise they would end up being undefined. The latter implies that physically we might regard these force messengers (i.e. ...
2
votes
0answers
35 views

Schwartz QFT solution

Is there a way I Can find a solutions manual for Matthew Schwartz's "Quantum Field Theory and the Standard Model" book?
1
vote
1answer
46 views

How does a $\Theta$ function arise in this correlator?

I am currently reading the paper by Coleman on Symmetry breaking in 2d, which can be found here. On page 262 (4th page in the document), he is evaluating the following distribution: $$ ...
0
votes
0answers
32 views

Thermal mass and Thermal Width

I have a question about understanding the physical interpretation of the thermal mass and width of a particle. If we consider a particle in a plasma (which lets say is in the early universe and so ...
1
vote
0answers
53 views

How to calculate the contour integration with branch point? [closed]

The question come from a Mutusbara Sum like this $${ \sum _{ { z=i\omega }_{ n } } { \frac { -\alpha E\pi }{ 4{ z }^{ 3 }\sqrt { -\alpha -z } } } }$$ it equal a contour integral around Imaginary ...
2
votes
1answer
83 views

Perturbativity of SM Higgs quartic coupling [closed]

I'm little confused about the maximal appropriate value for the SM Higgs quartic coupling. I know that the Higgs mass, $m_h= 125 \,\text{GeV}$ and that $ \lambda = m_h^2 / 2 v^2 \simeq 0.1 $ for $v = ...
0
votes
0answers
22 views

Elementary particles interaction time (in LHC, for example)

Feynman description of an interaction contains diagrams with different total time steps (that contribute only a little to the amplitude, I guess). Is there a calculation, for a given interaction, what ...
2
votes
3answers
280 views

Is Bohmian Mechanics incompatible with loop corrections?

For those who continue to be unsatisfied with Quantum Mechanics (QM), Bohmian Mechanics (BM) is an alternative worth considering. It is sometimes claimed that BM is equivalent to QM, but Lubos Motl ...