# All Questions

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40 views

### In QFT, are forces made out of multiple fields?

I’ve been reading about 1,5 books about quantum physics and I’ve also watched a few YouTube videos. In one book, I learnt that there are fields, such as the electromagnetic field, which carries forces ...
1answer
49 views

### Decay rate of scalar Yukawa interaction

Considering the Lagrangian of two scalar fields in $d=4$: $$\mathcal{L}=\frac{1}{2}(\partial\phi)^2-\frac{1}{2}m^2\phi^2+\frac{1}{2}(\partial\chi)^2-\frac{1}{2}M^2\chi^2-g\phi^2\chi$$ Let's assume ...
1answer
36 views

### Self-energy in two scalar Yukawa interaction

Considering the Lagrangian of two scalar fields in $d=4$: $$\mathcal{L}=\frac{1}{2}(\partial\phi)^2-\frac{1}{2}m^2\phi^2+\frac{1}{2}(\partial\chi)^2-\frac{1}{2}M^2\chi^2-g\phi^2\chi$$ What would be ...
2answers
90 views

### Why can't two real photon, gluon, graviton, and $W$ and $Z$ fields interact by means of their virtual counterparts (the mediators of the process)?

It is a fact that two real (massless) photons, gluons, or gravitons can't react by means of their virtual counterparts (for example, two external photons that interact via one of these massless ...
1answer
88 views

### Are force carrying particles always virtual particles?

Of course we have real (i.e. non-virtual) photons, but when photons play the role of "force carrier" are they virtual? Same thing for gluons. Real gluons have been detected, but when playing the role ...
1answer
77 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 ...
1answer
79 views

### Why coupling constants with negative mass dimensions lead to non-renormalizable theories?

can somebody explain or point to the relating mathematics showing Why coupling constants with negative mass dimensions lead to non-renormalizable theories?
0answers
30 views

### Deriving effective interactions, e.g. phonon-mediated electron-electron interaction

Upshot of the question: how can I derive the effective electron-electron interaction brought about by the electron-phonon interaction? I've read derivations of the electron-phonon interaction and ...
2answers
87 views

### Variance of an interacting quantum field in its vacuum state

A non-interacting quantum field $\hat{\phi}(x)$ can be decomposed into $a_{\textbf{k}}$ and $a_{\textbf{k}}^\dagger$. This enables us to calculate the variance of a free field. For example, the ...
1answer
91 views

### Interacting conformal field theories in spacetime dimensions higher 6?

Are there any papers which directly tackle the question of whether or not there exists interacting CFTs in spacetime dimensions higher than 6? It has been proven that there do not exist any ...
0answers
51 views

### Non-minimal coupling between a neutral atom and the EM field

Let us say that I have neutral bosonic atoms interacting with an EM field. I can write down the Lagrangian as \begin{align} \mathcal{L}=\eta^{\mu\nu}\partial_{\mu}\phi\partial_{\nu}\phi^{\dagger}-m^2|...
1answer
154 views

### What is the definition of “force” in quantum field theory?

In quantum field theory, there are certain interactions that we seem to associate with the action of "forces." For example, the exchange of a gauge boson between two matter particles is associated ...
1answer
42 views

### How to know what type of diagram contributes to a two-to-two process?

There are 3 types of diagrams that can contribute to a two-to-two process; the $s$-channel, $u$-channel and $t$-channel. How do I know what diagrams can contribute to a process? I know that in QED, ...
0answers
52 views

### Propagators in interaction with derivatives

Given a Lagrangian density containing an interaction with derivates, it's easy how to guess the Feynman rules for vertexes. However i was wondering about propagators: in S-matrix expansion it's ...
1answer
96 views