So-called radiative corrections

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SUMMARY

This discussion focuses on radiative corrections in Quantum Electrodynamics (QED) for absolute cross section measurements in lepton Deep Inelastic Scattering (DIS), Semi-Inclusive Deep Inelastic Scattering (SIDIS), and exclusive reactions. The participants clarify that elastic cross sections are effectively zero due to the strong coupling of charges and photons, leading to significant ultraviolet (UV) and infrared (IR) divergences. The inelastic cross section, however, remains measurable and is often what is experimentally observed, as it encompasses all final photon states. Key references include the publication "Atom as a 'dressed' nucleus" and "Reformulation instead of Renormalizations" by Vladimir Kalitvianski.

PREREQUISITES
  • Understanding of Quantum Electrodynamics (QED)
  • Familiarity with Deep Inelastic Scattering (DIS) and Semi-Inclusive Deep Inelastic Scattering (SIDIS)
  • Knowledge of cross section measurements and their significance in particle physics
  • Concepts of ultraviolet (UV) and infrared (IR) divergences in quantum field theory
NEXT STEPS
  • Research the implications of radiative corrections in QED
  • Study the differences between elastic and inelastic cross sections in particle physics
  • Examine the role of strong coupling in QED and its effects on scattering processes
  • Explore the publications "Atom as a 'dressed' nucleus" and "Reformulation instead of Renormalizations" for deeper insights
USEFUL FOR

Physicists, particularly those specializing in particle physics, quantum field theory, and experimental measurements of cross sections, will benefit from this discussion.

humanino
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Hi all,

is anybody familiar with (QED for simplicity) radiative corrections for absolute cross section measurements in lepton (electron) DIS, or SIDIS, or exclusive reactions ? I'd be glad if someone can brainstorm even on elastic cross section. I think I understand they are fairly different, but I'm unsure about the interpretations of the respective contributions of real and virtual corrections. UV divergencies cancel each other, but how about infrared ones ? Is it correct to say that we publish a "classical" cross section with Planck constant's going to zero, which is strictly zero at the quantum level ?

Thanks in advance for sharing your thoughts.
 
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humanino said:
Thanks in advance for sharing your thoughts.

Dear Humanino,

As soon as you invite to share thoughts, I can do it as I see it.

If we speak of QED, we have charges and photons in the initial and final states.
According to the QED's equations, charges and the quantized EMF are permanently coupled.
The calculation difficulties (UV and IR divergences) arise just because this coupling is strong rather than weak. Any charge scattering is accompanied with radiation so no elastic events are possible. It means the exact elastic cross section (or amplitude) is identically equal to zero. Now, as soon as in the zeroth-order the elastic amplitude is not equal to zero, the remaining perturbation series serves just to cancel it.

What is different from zero is the inelastic cross section which is the sum over any final photon state cross sections. It makes sense because experimentally one does not distinguish elastic from inelastic (in photons) cross sections - one observes only final charges whatever photon final states are. So experimentally it is the inelastic cross section which is usually measured. The most famous example is the Rutherford cross section. Rutherford could not observe the final target atom states but hey were excited ones. You can find details of this physics in my publication "Atom as a "dressed" nucleus" in arXiv or at the Central European Journal of Physics site. You will see that any particular excited (inelastic) cross section is quite particular - it depends on h_bar, but their sum is reduced to the elastic cross section from a point-like target (Rutherford cross section). There and in "Reformulation instead of Renormalizations" by Vladimir Kalitvianski you can find my thoughts about how it could be described naturally and without divergences.

Bob_for_short.
 

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