Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

So-called radiative corrections

  1. Jun 25, 2009 #1
    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.
     
  2. jcsd
  3. Jun 26, 2009 #2
    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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook