Talk:Photon structure function

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Conservation of momentum

Given that a photon does not have a rest frame, while a pair or system of massive particles do, photon disintegration seems to violate the conservation of momentum. Should the article discuss this? 80.220.18.127 (talk) 09:25, 24 June 2014 (UTC)[reply]

In any frame a photon has non-zero momentum. Why should it matter that it doesn't have a rest frame? --Lambiam 12:42, 24 June 2014 (UTC)[reply]

The photon disintegration is embedded into a more comprehensive scattering process as depicted in Fig.1. While disintegration is valid at high energies, the comprehensive process obeys momentum conservation strictly, and it is valid for any kinematical configuration.

Structure function vs. form factor

The photon structure function is defined by the inelastic process e γ → e+hadrons. Form factors are defined by elastic processes e N →e N for hadronic targets N, mediated by virtual photon exchange. But not for the photon target: the amplitude e γ → e γ vanishes for virtual photon exchange. Thus a discussion of form factors does not apply to photons and the corresponding subsection has been removed as a result.