What is the meaning of a collinear photon in Quantum Electrodynamics (QED)?

[ndung200790]

Please teach me this:
What is collinear photon (emission)?I do not understand why call ''collinear'' photon.
Thank you very much for your kind helping.

 

[mathman]

I am not sure of the the context of your question. If you are asking about stimulated emission (lasers), then the stimulated photon goes in the same direction (reinforces) the stimulating photon, so they are collinear.

 

[ndung200790]

In this case,the photons related with the p$^{+}$,
p$^{-}$ and p$_{\bot}$ .

 

[mathman]

In this case,the photons related with the p$^{+}$,
p$^{-}$ and p$_{\bot}$ .

Could you define these symbols?

 

[ndung200790]

Thank you very much for your kind heart.Now I have realized the singularities because ''collinear'' photon meaning scattered angle of photon equal pi in QED at very high energy.