Are photons the antiparticle of itself?

  • Context: Graduate 
  • Thread starter Thread starter PhotonicBoom
  • Start date Start date
  • Tags Tags
    Feynman diagram Photons
Click For Summary

Discussion Overview

The discussion revolves around the nature of photons as potential self-antiparticles, exploring their interactions and annihilation processes, particularly in the context of quantum electrodynamics (QED) and particle physics. Participants delve into theoretical implications, Feynman diagrams, and the behavior of bosons and their interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that photons can be considered their own antiparticles, with one stating they are "literally" their own particle.
  • It is suggested that photons do not annihilate because they are bosons and can occupy the same quantum state, while others clarify that there is no direct interaction between two photons.
  • Participants discuss Feynman diagrams, noting that while particle-antiparticle annihilation can produce photons, the fundamental QED vertex involves charged particles and photons.
  • Some participants mention that two photons can scatter or indirectly interact through other particles, such as electrons, leading to different outcomes like neutrino-antineutrino pairs.
  • There is a query about whether boson-antiboson pairs can annihilate, with responses indicating that they can, citing examples like electron-positron annihilation.
  • Discussion includes the nature of composite particles like pions, with some participants questioning their classification as bosons due to their internal structure and the implications for annihilation processes.
  • One participant expresses uncertainty about whether pions are bosons, noting their composite nature and the behavior of their constituent fermions.
  • Another participant asserts that pions obey Bose-Einstein statistics, confirming their classification as bosons, but acknowledges the limitations of this classification at certain energy levels.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the nature of photons and pions, as well as the interactions of bosons. While some points are accepted, such as photons being their own antiparticles, other aspects, particularly regarding annihilation processes and the classification of composite particles, remain contested and unresolved.

Contextual Notes

Participants highlight limitations in understanding interactions, such as the dependence on definitions of particles and the complexities introduced by composite structures. There is also mention of unresolved mathematical steps in the context of Feynman diagrams.

PhotonicBoom
Messages
9
Reaction score
0
Hey guys, I was thinking about this for a while now and I seem to be on a dead end. So here it is, this is my speculation. I would love some feedback, tell me which parts are correct/false and if they are false, guide me towards the right path! :)

1. Photons can technically be their own antiparticle.

2. They don't annihilate because they are bosons and can occupy the same quantum state.

3. In many Feynman diagrams we see a particle & antiparticle annihilation producing another particle and antiparticle pair. I was thinking that's why we get 2 photons in some other annihilation interactions (one photon, one antiphoton)

I must be missing something. Is my logic flawed?
 
Physics news on Phys.org
Sure they are, and they can be viewed as being their own antiparticle.
 
PhotonicBoom said:
3. In many Feynman diagrams we see a particle & antiparticle annihilation producing another particle and antiparticle pair. I was thinking that's why we get 2 photons in some other annihilation interactions (one photon, one antiphoton)

You cannot have a QED Feynman diagram with two photon lines at a vertex. The fundamental vertex of the QED interaction consists of two electron (charged particle) lines and a photon line. You can certainly have the scattering ##\gamma + \gamma \rightarrow \gamma + \gamma##, which is called Delbruck scattering, but this is a four vertex diagram at the lowest order and consists of 4 external photon lines and 4 internal electron lines since higher order QED diagrams can only be built up from the fundamental vertex.

None of this is contradictory to the (correct) statement that photons are their own antiparticles.
 
PhotonicBoom said:
1. Photons can technically be their own antiparticle.
Photons ARE their own particle. Literally, not just technically.

PhotonicBoom said:
2. They don't annihilate because they are bosons and can occupy the same quantum state.
Two photons don't annihilate because there is no direct interaction between two photons. Indirectly, through their interaction with other particles such as electrons, two photons can scatter, or turn into a neutrino-antineutrino pair.

PhotonicBoom said:
3. In many Feynman diagrams we see a particle & antiparticle annihilation producing another particle and antiparticle pair. I was thinking that's why we get 2 photons in some other annihilation interactions (one photon, one antiphoton)
It's conservation of momentum, angular momentum and parity that requires two photons to be produced, or sometimes three of them.
 
Thanks a lot to everyone for the responses!

Bill_K said:
Two photons don't annihilate because there is no direct interaction between two photons. Indirectly, through their interaction with other particles such as electrons, two photons can scatter, or turn into a neutrino-antineutrino pair.

Can two boson pairs (boson - antiboson) annihilate in general? Since they can occupy the same quantum state I thought they wouldn't.
 
PhotonicBoom said:
Can two boson pairs (boson - antiboson) annihilate in general? Since they can occupy the same quantum state I thought they wouldn't.
Sure, no problem. The simplest example comes from e+ + e- → γ + γ. Just run it backwards: γ + γ → e+ + e-.

Most examples are unobserved, but that's just because it's more difficult experimentally to collide two bosons, since they tend to decay! But in principle, π+ + π-, or W+ + W- are annihilation examples.

Having two bosons just means that their two-particle wavefunction is symmetric, so e.g. they could orbit each other in an S state.
 
Bill_K said:
Most examples are unobserved, but that's just because it's more difficult experimentally to collide two bosons, since they tend to decay! But in principle, π+ + π-, or W+ + W- are annihilation examples.

just a remark:
Wouldn't it be better to avoid the pions? fundamentally the annihilation still occurs between two fermions.
The rest OK
 
ChrisVer said:
just a remark:
Wouldn't it be better to avoid the pions? fundamentally the annihilation still occurs between two fermions.
The rest OK
Are you saying that pions are not bosons??
 
  • #10
Bill_K said:
Are you saying that pions are not bosons??

No I am not saying that.. they are not fundamental (consisting of (anti)quarks which are fermions), and the annihilation happens between the quarks (fermions).

Also
I am not sure whether they are bosons or not...since they have inner structure, they will tend to behave like bosons, but only effectively...there are also bosonic nuclei but they also behave like that effectively because they have fermionic inner structure (nucleons)
maybe I'm wrong or missing something
 
  • #11
ChrisVer said:
I am not sure whether they are bosons or not...since they have inner structure, they will tend to behave like bosons, but only effectively...there are also bosonic nuclei but they also behave like that effectively because they have fermionic inner structure (nucleons)
maybe I'm wrong or missing something

Pions obey Bose-Einstein statistics - > Bosons :)
 
  • #12
PhotonicBoom said:
Pions obey Bose-Einstein statistics - > Bosons :)

Yeah, but only at energies so their constitute fermions aren't relevant - a composite boson can not break the exclusion principle for its constituents!
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 16 ·
Replies
16
Views
5K
  • · Replies 0 ·
Replies
0
Views
453
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 58 ·
2
Replies
58
Views
5K
  • · Replies 9 ·
Replies
9
Views
2K