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1answer
119 views

Feynman diagram for Hawking radiation?

I'm starting to wrap my head around Feynman diagrams, and the idea of "real" vs. "virtual" particles, but one area where this distinction seems to break down is in describing Hawking radiation, where ...
9
votes
2answers
232 views

Are unstable particles ever “real”?

It's always stressed that internal lines of Feynman diagrams have no physical meaning, that is, they don't actually correspond to anything physical. Where this confuses me is in the case of unstable ...
2
votes
2answers
46 views

Do virtual mesons exchanged between nucleons in the nuclear force ever decay before reaching the recipient nucleon?

So my understanding of the nuclear force so far is this (please correct anything I have wrong): Being a residual of the strong force, the nuclear force is mediated (in part) by the emission of ...
0
votes
0answers
48 views

Question about Bhabha scattering Feynman Diagram

I'm a uni student going into his third year, and thought I might try to read through Griffith's particle physics textbook for the heck of it. I've been trying to become familiar with Feynman diagrams, ...
0
votes
1answer
34 views

What parameters determine the probability of virtual photon emission/absorption?

Suppose an electron is producing an electric field by emission of virtual photons and interacting with other particles. What parameters determine the probability that it will emit at least one virtual ...
0
votes
2answers
81 views

Why can't a particle interaction $A + B \rightarrow C$ conserve energy and momentum at the same time?

I learned that in the Feynman diagram for electron photon scattering, the intermediate particle represented by the middle solid line must be a virtual particle because it violates energy-momentum ...
3
votes
3answers
211 views

Feynman diagrams

Feynman diagrams are drawn on Space-time graphs. So is it possible for any particle path in that diagram to have a slope smaller than 45° or greater than 135°, i.e. can they travel faster than light? ...
1
vote
0answers
139 views

Why isn't energy conserved in time-ordered diagrams?

I'm new to particle physics, and I'm reading chapter 5 of Prof. Mark A. Thompson's "Modern Particle Physics", which talks about Time-ordered perturbation theory vs QED. However, in page 119 he wrote: ...
1
vote
1answer
285 views

How to interpret the Feymann diagram of two photons scattering off each other?

I've attached a Feynmann diagram of two photons scattering with the nuclear reaction: γ + γ --> γ + γ May I ask how would one interpret this diagram? My attempt in interpreting is that the photon ...
2
votes
1answer
320 views

Why can there be only 3-particle vertices in Feynman diagrams? [closed]

Why can there be only 3-particle vertices in Feynman diagrams? For example, when a particle and its anti-particle annihilate to form two photons, why is its Feynmann drawn the way it is in diagram 2 (...
2
votes
1answer
257 views

How does virtual particle explanation of Hawking radiation contradict with consistent loop description?

the picture of virtual particle pairs is categorically not the right way to think about Hawking radiation. Quite obviously it must be wrong, because it is a loop level effect, and loops in QFT have to ...
1
vote
1answer
97 views

How to describe the phase change for a charged matter wave in an external magnetic field using virtual photons?

In the case of an electron travelling through a region with an external magnetic field, experiments show that the field changes the phase of the electron wave function. The phase change depends on $B$ ...
2
votes
0answers
132 views

External momenta vs loop momenta in Feynman diagrams

In Peskin and Schroeder's book on QFT, the second paragraph of chapter 12 says, In a renormalizable theory, the loop integrals over virtual-particle momenta are always dominated by values ...
5
votes
5answers
722 views

Why does an electron react differently to a virtual photon in the interaction between two electrons and between an electron and a positron?

For the interaction between, say an electron and a positron, there correspond many (infinite) Feynman diagrams with well described mathematical expressions for the incoming and outgoing particles and ...
-1
votes
1answer
121 views

If virtual particles is not real, what are the lines in Feynman diagram?

Since virtual particles is not real, than what are the curved lines in the Feynman diagram if it is not virtual particles?
1
vote
1answer
325 views

Virtual Photon in Electron Scattering Feynman diagram [duplicate]

If we know that the virtual photon emitted in an electron scattering Feynman diagram violates the energy and momentum conservation laws (though temporarily), why do we accept it as a feasible diagram ...
1
vote
1answer
177 views

Line constant in time in Feynman diagrams

I just started reading about Feynman diagrams in Griffith's Introduction to Elementary Particles. Using the convention that time goes to the left, and arrows pointing forward in time represent ...
2
votes
2answers
714 views

Where does $W$ boson mass come from in neutron decay?

Here's a diagram of neutron decay. Up and down quarks have rest masses of 2-4 MeV. The $W$ boson has a rest mass of 80 GeV. Where has this extra mass come from?
0
votes
2answers
479 views

What particles do these Feynman diagram lines represent?

What particles could be represented by A and B (labels I have added myself - this is not a homework question)? For A, it looks like it's supposed to be a photon, but I was under the impression that ...
2
votes
2answers
323 views

Feynman diagram, which virtual particle?

Hi I have been asked to produce the lowest order Feynman diagram for the following scattering process: $$a.~~~ \mu^-+\mu^-\rightarrow \mu^-+\mu^-$$ $$b.~~~ \mu^-+\mu^+\rightarrow \mu^-+\mu^+$$ The ...
3
votes
1answer
734 views

Do we really need virtual particles to exist?

I understand the $\Delta t \cdot \Delta E \geq \hbar / 2$ relationship and the idea behind them. However, I don't understand why do we need them at all. I'm a physics undergraduate. As far as I know, ...
32
votes
4answers
10k views

Do virtual particles actually physically exist?

I have heard virtual particles pop in and out of existence all the time, most notable being the pairs that pop out beside black holes and while one gets pulled away. But wouldn't this actually violate ...
1
vote
2answers
1k views

Having Trouble Understanding Feynman Diagrams [closed]

So recently I have became interested in quantum physics. However when I read up on quantum physics Feynman diagrams appear everywhere, and I do not understand them! Here is a Feynman diagram that is ...
4
votes
1answer
1k views

Why don't virtual particles violate conservation of mass/energy?

If virtual particles sometimes add more mass/energy to a system then was inputed or comes out in the output, how do they not violate conservation of mass/energy.
3
votes
3answers
527 views

Feynman paths of FTL velocity have imaginary momentum?

In this Phys.SE answer it is discussed that Feynman path integrals sums amplitudes for all possible paths, including those that are not time-like. If you take the momentum-space path integrals, I ...
1
vote
1answer
90 views

Outside of string theory, can exchange particles be understood as being one-dimensional?

I'm pretty new to quantum, without any formal education therein, so forgive my general layman ignorance when I ask how it is that point-like exchange particles can be modeled in Feynman diagrams as ...
2
votes
1answer
365 views

Virtual Photon transmission speed of a Static Electric Field?

In the case of a non-accelerating point charge "A" of stable velocity, its static field is treated as though it is instantaneously present at a distance, i.e. a second point charge "B" will react to ...
3
votes
3answers
607 views

How does a photon “know” that it's left one charge and that it's going to another one?

How does it know the same charge it left will be the same charge it will return to? My understanding is photons are neutral and have no charge. i.e. Like charges repel, unlike attract. All charged ...
3
votes
0answers
234 views

Feynman Toy Model Constraints on Number of Each Kind of External Lines

(From my homework) In our toy model we have three kinds of spinless particles: $A$, $B$, and $C$. The primitive vertex of decay/interaction is shown below: My actual problem statement says: "...
13
votes
3answers
806 views

Does radio use virtual photons?

In radio communication each accelerated electron in the transmitter antenna interacts with an electron in the receiver antenna by exchanging a photon. Is that photon always a virtual photon as ...
3
votes
0answers
58 views

Scattering theory on Schrodinger and Feynman languages

Recently I heard that both of "languages" of scattering theory (formal solution by method of classical scattering theory and its reworking by Feynman with his rules) predict virtual particles. But for ...
7
votes
1answer
594 views

Quantum Electrodynamics

I was wondering if anyone could give a simple explanation of how light interacts with matter. From what I have read in QED, electrons will repel each other because of their ability to emit and ...
7
votes
3answers
1k views

What makes a Feynman diagram real or virtual?

Simple question: as the title says, what makes a real Feynman diagram real, and what makes a virtual diagram virtual? Or in other words, how do I tell whether any given diagram is real or virtual? I'...
6
votes
2answers
1k views

How do we distinguish between virtual particle exchange and particle decay?

The difference between virtual particles and unstable particles is discussed at length in this question (namely, virtual particles correspond to internal lines in Feynman diagrams and are not ...
3
votes
2answers
555 views

Does path integral and loop integral in a Feynman diagram violate special relativity?

Consider a correlation function between two points $A(x_1,t_1)$ and $B(x_2,t_2)$, we need to integrate over paths which could be infinite long. But the time length $(t_1-t_2)$ is finite, so if $A$ and ...