meta user
network profile
| bio | website | |
|---|---|---|
| location | ||
| age | ||
| visits | member for | 10 months |
| seen | 10 hours ago | |
| stats | profile views | 546 |
DM
|
2d |
comment |
“Slightly off-shell”? Ron, what is "your" definition of the mass of virtual particles, say, photons? Zero or $p^2$? In the former case there is superluminal propagation, in the latter case the mass may be an imaginary number (!). |
|
May 13 |
comment |
Is all matter made of virtual particles? let us continue this discussion in chat |
|
May 13 |
comment |
Are W & Z bosons virtual or not? Well, I guess it is trivial for particles with spin... |
|
May 12 |
comment |
Are W & Z bosons virtual or not? Okay thanks @RonMaimon , but it isn't in Polyakov's book. A Feynman diagram beyond tree level using this formalism would help. I don't even know how to write the Feynman propagator of a non-scalar field in terms of a relativistic particle path. |
|
May 12 |
comment |
Is all matter made of virtual particles? By the way, I would like to know your opinion about the very complete Neumaier's answer physics.stackexchange.com/questions/4349/… Thank you in advance. |
|
May 12 |
comment |
Is all matter made of virtual particles? You also say that quarks are always virtual (because of confinement and your first definition). However, when you compute, say, the tree-level cross section $\sigma (e^-\, e^+ \rightarrow q\, \bar q)$ at centre of mass energies much higher than 1 GeV the quarks are on-shell, they are final states belonging to the Hilbert space. In your opinion/definition, is there any relation between non-virtual (i.e., real) particles and states in a Hilbert space? Are you identifying free particles with real particles and interacting particles with virtual particles? |
|
May 12 |
comment |
Is all matter made of virtual particles? Hello Anna, so interesting. I was doing a little of research about the use of the term "virtual particle" and I'm astonished by your answer. What is the definition of "virtual particle" you are using? It seems that you call "virtual particle" to each component or interacting particle (elementary or not) of a bound state (hadrons, nucleus, atoms,etc) while "real particle" to the whole system (first time I see this). But at the same time you identify virtual particles with "those" that aren't on-shell (this is closer to the definition I'm familiar with). |
|
May 11 |
comment |
Are W & Z bosons virtual or not? Appreciated @RonMaimon, I'm very interested in learning more about virtual particles and Feynman diagrams in space-time. Could you please expand your first comment to this answer or give me some reference (post, book, paper, etc)? I know how to express the euclidean field propagator in terms of the path integral of a relativistic particle, but not much more. |
|
Apr 20 |
comment |
When can a global symmetry be gauged? Let me point out that the reason why my argument does not work is because one would need a real, massless Klein-Gordon field. Real and Klein-Gordon are no problem. The problem is "massless" since then one cannot take the non-relativistic limit. |
|
Apr 18 |
comment |
When can a global symmetry be gauged? Thanks and sorry, but I do not understand that. 1)The non-relativistic limit of a real Klein-Gordon field is a (complex) Schrödinger field. The former obeys a 2nd order EOM, while the latter a 1st EOM. So one physical degree of freedom in both cases. 2) The transformation is uniparametric so that there is only one generator ($\int \, \theta \, \psi^{\dagger} + h.c.$). Sorry about the brevity, I'm in a rush. @DavidBarMoshe |
|
Apr 18 |
comment |
What really are superselection sectors and what are they used for? I have just noticed I mistakenly down-voted this question when I tried to up-vote it. Sorry about this, Dilaton. I would need you to edit your question to undo the down-vote. |
|
Apr 17 |
comment |
When can a global symmetry be gauged? I think that one can gauge this symmetry, which is the responsible of the renormalizability of Proca theory physics.stackexchange.com/questions/16931/… Have you read the opposite? Ref or link? |
|
Apr 12 |
awarded | Excavator |
|
Apr 12 |
revised |
If : V(Phi) : is nonlocal in space, does that mean interacting quantum field theory is nonlocal? In the first line of the last paragraph: temporal ---> normal |
|
Apr 12 |
comment |
Why is $R^2$ gravity not unitary? The problem is either the theory is unstable (the Hamiltonian is not bounded from below) or contains states with negative norm (the former is the real problem, and the latter is why it is said that theory is not unitary). It is a general problem of theories with higher order timer-derivatives. |
|
Apr 12 |
suggested | suggested edit on If : V(Phi) : is nonlocal in space, does that mean interacting quantum field theory is nonlocal? |
|
Apr 9 |
comment |
How does the quantum path integral relate to the quantization of energy? Thank so much David Bar Moshe. Your contribution is invaluable. |
|
Mar 15 |
comment |
Would a spin-2 particle necessarily have to be a graviton? Sorry: where it says "weak interactions —which are parity invariant—", it should obviously say "weak interactions —which are not parity invariant—" |
|
Mar 14 |
comment |
Would a spin-2 particle necessarily have to be a graviton? (cont.) much like massless neutrinos: neutrinos have helicity $-1/2$ and antineutrinos helicity $+1/2$. This is due to neutrinos interact weakly and weak interactions do not preserve parity. |
|
Mar 14 |
comment |
Would a spin-2 particle necessarily have to be a graviton? @Xiao-GangWen Particles are classified according to the irred. repr. of the proper orthocronus Poincare group. The helicity is invariant under these transformations (it is a pseudo-scalar). The only reason why both helicities are considered the same particle —although strictly speaking are not— is that photons just interact through interactions that respect parity and both helicities are related by a parity transformation. If photons also interacted through weak interactions —which are parity invariant—, $\pm 1$ helicities would be considered different particles, |
