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)

0
votes
0answers
27 views

How do we know that A is a pseudoscalar (CP-odd) Higgs?

Starting from a model with two complex Higgs doublets (as e.g. in the MSSM) we arrive at 5 physical Higgs bosons (instead of 1 as in the Standard Model), 2 of which are charged and 3 are neutral. One ...
1
vote
1answer
89 views

How does a particle's spin z component changed under lorentz group [closed]

I am reading weinberg's QFT, on the page 104, exercise 1, He said an observer $O $ see a W-boson (spin one and mass m) with momentum $p $ in the y direction and spin z-component $\sigma$ . a second ...
0
votes
0answers
53 views

Bogoliubov coefficients and eigenvectors

Suppose you have diagonalized Hamiltonian $H$ in second quantization using Bogoliubov transformation. If Hamiltonian is $N \times N$ matrix, the Bogoliubov transformation will have $N$ coefficients. ...
2
votes
0answers
28 views

Are there any video lectures that teach Weinberg's QFT books? [duplicate]

I am reading Weinberg's QFT books. I wonder is there any course can help me with it.
3
votes
0answers
30 views

Surreal Trajectories in Bohmian Mechanics [duplicate]

In February of this year, articles started popping up describing the results reported in this paper by Mahler et al: http://advances.sciencemag.org/content/2/2/e1501466.abstract Taken from this ...
1
vote
1answer
108 views

What is “the scale at which a theory is defined”?

I'm trying to learn the renormalization group, but I am confused about renormalization schemes. The general idea of RG is that physical predictions are independent of "the scale at which a theory is ...
0
votes
0answers
18 views

A few positrons collide with a solid body at rest; what can happen?

Suppose we have a macroscopic solid object. Now we have a beam of Positrons that is injected into this solid Body at vacuum. What can happen? There will take place a pair Annihilation of electrons ...
2
votes
1answer
57 views

Canonical field momentum in quantum field theory

In the context of the second quantization and the use of fields in the canonical quantization, the canonical momentum of the field is defined as the derivative of the field by the time coordinate. But ...
7
votes
1answer
182 views

Restoration of spontaneously broken symmetry at high energy

It is common to find books saying that above a certain energy, a certain symmetry in particle physics is restored, e.g. the $SU(2)\times U(1)$ electroweak symmetry was unbroken between $10^{-36}$ to ...
10
votes
3answers
214 views

Is the “number of photons” of a system a Lorentz invariant?

I'm wondering whether the number of photons of a system is a Lorentz invariant. Google returns a paper that seems to indicate that yes it's invariant at least when the system is a superconducting ...
1
vote
0answers
55 views

Wave function of the universe - universes similar to ours [closed]

According to this image, the first peak in the graph corresponds to our universe while the other peaks correspond to other, less probable universes. But what do points slightly right (or left, ...
1
vote
1answer
49 views

Addtional QFT Book synergetic to Srednicki. Differences $\phi^4$ and $\phi^3$ [duplicate]

I currently hear a course to basic QFT in path integral formulation. Focus is on few and elementary particles, not on many body systems. The lecturer follows the book of Srednicki, which therefore ...
0
votes
0answers
48 views

About the non-locality of gravitational energy 2

Gravitational energy is non-local which is essentially because of the equivalence principle. The equivalence principle says that you can always transform your frame so that you feel like in a ...
3
votes
1answer
81 views

Can I catch a particle (such as electron) and say it's left hand

Why is only the left hand electron coupled to weak interaction? How can I tell the chirality of an electron?
0
votes
1answer
34 views

Massive spin one pseudovector decay?

Suppose you have a massive spin one pseudo-vector particle. Is it allowed to decay into an electron-positron pair? I'm thinking it might be disallowed because of parity conservation. If it is ...
-1
votes
1answer
78 views

Commutation relations in Quantum Field Theory [closed]

\begin{align} [a, a^\dagger] =& \left[\int d^3 x e^{-ikx} (\omega \phi(x) + i \Pi^\dagger(x)), \int d^3 x' e^{ikx'} (\omega \phi^\dagger(x') - i \Pi(x')) \right] \\ =& \int d^3x \, d^3x' \, ...
1
vote
0answers
23 views

relative minus sign in radiation of gluon jets

I am trying to calculate the cross-section for electron-positron annihilation into a quark-antiquark pair and a gluon. I find that I need a relative minus sign between the two contributing diagrams in ...
0
votes
4answers
202 views

Why do we say that photons are particles? [closed]

This question may appear stupid but I really do have to understand. Maybe it's just semantic and nothing else. Why do we say that photons are (elementary) particles? They are pure radiation, since ...
4
votes
0answers
58 views

Momentum eigenstate definition in Eq (2.5.5) of Weinberg Vol. 1 clairification

This is question is related to one asked here: Questions concerning some parts of the section on one-particle states in Weinberg's first volume on QFT. In Eq (2.5.5) of Weinberg's "The Quantum ...
1
vote
1answer
59 views

Why group elements associated with gauge transformations of finite action field configurations in QCD don't depend in $r$?

I am reading the chapter on instantons in Coleman's Aspects of Symmetry. I am puzzled by an argument i don't quite follow. In section 3.2, Coleman considers configurations of the gauge field with ...
0
votes
0answers
48 views

Expansion operator for quantum mechanics

As a counterpart to the quantum mechanical translation operator (see for example this post) is there a unitary operator which describes the stretching of a line. That is consider I have a chain of ...
9
votes
0answers
118 views

time-dependent Hartree-Fock for two-component bosons

How does the ansatz for the time-dependent Hartree-Fock wavefunction look like in the second quantization if we have two-component boson system and in one case the Hamiltonian commutes with number of ...
0
votes
0answers
49 views

How to construct effective interaction vertex?

In literatures, I often come across interactions like the $D^*D\gamma$ vertex: $$\mathcal{L}_{D^*D\gamma}(x)=\frac{e}{4} \epsilon^{\mu \nu \alpha \beta} F_{\mu \nu}(x)\left({g_1} D^{*-}_{\alpha ...
1
vote
0answers
34 views

Yukawa interaction and four fundamental forces [closed]

What is the difference(or relation) between Yukawa interaction($\mu\bar{\psi}\phi\psi$) and the other four fundamental interactions(e.m., weak, strong and gravity)? Does it fall anywhere on the ...
3
votes
2answers
191 views

In quantum field theory, how can Compton scattering change the frequency of light?

Classically, when light scatters off matter, the frequency of the light must stay the same. This follows directly from a continuity argument: if you put in $f$ field oscillations per second, you'd ...
1
vote
1answer
51 views

Simple feynman parameters question

I have the following integral $$\int d^D l \frac{1}{p^2 (p-l)^2 l^2}$$ which I want to rexpress using feynman parameters. I can write as a first step, $$2 \int_0^1 dx \int_o^{1-x} dy \int d^D l ...
4
votes
1answer
86 views

Why does a Heisenberg magnet break the O(3) symmetry in stead of SU(2)?

As stated in the question, why does a Heisenberg magnet break the $O(3)$ symmetry while degrees of freedom of the underlying spins are $SU(2)$?
1
vote
0answers
68 views

On shell and off shell simultaneously?

I am considering the following one loop virtual correction in the DIS process: where I have a quark of momentum $p$ coming in, emitting a gluon before interacting with a photon of momentum $q$ to ...
0
votes
0answers
47 views

Single-particle operator in second quantization

I am new to second quantization and I am still rather uncomfortable with the bra-ket notation. I feel like I am slowly getting the hang of it but when it comes to shifting bra's and ket's around, I ...
3
votes
1answer
49 views

Is a system of free spinless fermions always critical?

Consider a system of free spinless fermions, whose Hamiltonian can be written as $$ H = \sum_{i,j}h_{ij}a_i^\dagger a_j-\lambda\sum_i a^\dagger_i a_i $$ with $h_{ij}=h_{ji}^*$ scalars and ...
0
votes
0answers
31 views

Derivation of Functional Renormalization Group Equation in non-zero spin particles

I know the functional renormalization group equation(also known as Wetterich Equation) is $\partial_k \Gamma_k = \frac{1}{2} \text{STr} \, \partial_k R_k \, (\Gamma^{(2)}_k + R_k)^{-1},$ and ...
5
votes
0answers
81 views

TQFT's as effective theories of the groundstate subspace

I often hear: "The degenerate groundstate subspace of a QFT is often a TQFT". I'm trying to work out an example of this for, say, superconductors: In the context of condensed matter physics, the ...
3
votes
2answers
89 views

Is QFT time symmetric, and how is it implemented?

In electromagnetism, while the Maxwell equations are time symmetric, there is a choice to restrict solutions specifically to retarded potentials, imposing a time direction on the equations. And in ...
0
votes
0answers
20 views

Nonequilibrium Green's functions weakly interacting two-component Bose gas

I am planing to describe time evolution of two-component BEC. I was thinking about non-equilibrium Green's functions, but I don't if the method can be applied to the problem describe below. I know ...
0
votes
0answers
47 views

$i\epsilon$ in CFT correlation functions

M. Luescher in his talk on p.6 writes that the 2-point correlation function of a Hermitian local field $O_k$ of scaling dimension $d=3-k$ looks like $$ \langle 0| O_k(x) O_k(y) |0\rangle = A_k (x-y-i ...
2
votes
1answer
50 views

Would the existence of more than 16 quark flavors make QCD deconfinning?

Consider the QCD beta function. Its expansion in powers of the coupling is $$\beta(\mu)=-(\beta_0a(\mu)+\beta_1a^2(\mu)+\ldots)$$ where $a=\alpha/4\pi$. For simplicity let's neglect everything but ...
0
votes
0answers
19 views

IBP application in feynman box diagram

I'm trying to calculate the box diagram also mentioned in this question, but with the Integration by Parts (IBP) identities. At first, if I neglect all the external momenta for a moment, I get $$\int ...
0
votes
1answer
58 views

Computing the pole mass from a given $\overline{MS}$ mass?

Given a Yukawa coupling as a function of scale $\mu$ and a vev, therefore $m_R(μ)=Y(μ)⟨ϕ⟩$, how can I compute the corresponding pole mass $m_p$? Relations I was able to find are (page 39) ...
0
votes
0answers
52 views

How to get anti-commuting rule from the view of field?

I was reading the 1951 Lectures on Advanced Quantum Mechanics and I found something really disturbing. That's the anti-commuting rule mentioned on Page 40 at last. Though it was named as Quantum ...
0
votes
0answers
37 views

Why does the cup stay on the table? [duplicate]

The question is in the title. It is a very simple question and I am asking myself if this is only the reason of electron repulsion and the Pauli principle or what else comes into play to answer this ...
0
votes
0answers
51 views

Particle creation through a time dependent Hamiltonian

We know that a time dependent Hamiltonian can create particles. We know this for instance from field theory in curved spacetime, where for instance in an expanding or contracting universe creation and ...
3
votes
1answer
85 views

Vacuum has both zero four-momentum and nonzero vacuum energy?

I have heard that in QFT, the vacuum has zero four-momentum: $$P^\mu |\Omega \rangle = 0.$$ However, I also know that the vacuum has vacuum energy, i.e. $$ \langle \Omega | H | \Omega \rangle = E_0 ...
0
votes
0answers
48 views

Solving non scalar integrals in loop calculations

Consider the following integral that comes out of a loop calculation along with some fermionic propagators (e.g virtual one loop correction to a $p \gamma^* \rightarrow p'$ process such as in DIS): $$ ...
0
votes
0answers
35 views

Gauge invariance of quantum scalar field coupled to classical electromagnetic potential

I would like to quantize a scalar field that is coupled to a classical electromagnetic field $A_\mu$. More precisely, I start with the action (signature -+++) $$ S=\int ...
3
votes
1answer
79 views

Renormalisation group equation for Green's functions

The renormalization group equations for the $n$-point Green’s function $$\Gamma(n) = \langle \psi_{x_1} \dots \psi_{x_n}\rangle $$ in a four-dimensional massless field theory are $$\mu \frac{d}{d ...
1
vote
0answers
31 views

Decay rate and differential cross-section

If I have a $pp-$beam producing an on-shell particle $A$, which then decays into particle $B+C$, then I can find the total cross-section $pp \to A \to B+C+Y$ ($Y$ being inclusive particle which should ...
1
vote
0answers
39 views

Symmetries of a Lagrangian density

Given some Lagrangian density as this how in general can one finds it's symmetries that give conserved currents? For example in this case U(1) is ok, but are there others? Do you know some book ...
0
votes
0answers
30 views

Charge conjugation and the conserved charge for the Dirac field

So, while reading Peskin & Schroeder's chapter on the Dirac field, they claim that the charge conjugation operator has the following properties: $$ \mathcal{C}\psi(x) \mathcal{C} = -i \gamma^2 ...
3
votes
2answers
105 views

Question about source terms in scalar quantum field theory

I'm having a bit of a mental block when trying to interpret the inhomogeneous Klein-Gordon equation $$(\Box +m^{2})\phi(x,t)=j(x,t)$$ In particular, how does one interpret the term on the right-hand ...