Question

What is the phase space for outgoing photons?

Answer 1

or a scattering process for which nn fermions are scattered, (by some conventions) the cross section acquires a phase space factor of:

dσ∼∏i=1nd3pi(2π)32Eidσ∼∏i=1nd3pi(2π)32Ei

In this convention, what is the equivalent phase space factor for an outgoing photon?

How is it that different conventions differ by arbitrary factors of 22 and ππ? isn't the cross section a measurable which has to "stay put" irrespective of the convention used?

Answer 2

Hey mate here is your answer...

1. it's the same expression for the photon as for any other particle (just remember that you are overcounting the phase space if the particles are identical, and need to include a factorial factor to get it right) 2. the cross-section is notation independent, but you have written just the phase space, not the full cross-section. The independent quantity is phase-space times |scattering amplitude|^2. If your convention for the phase-space differs by a factor of 2 then the convention for the scattering amplitude differs too, and by a factor of 1/2–√

Hope it helps you........!☺️☺️