1. Radiative Corrections : selected comments
Eduard. A. KURAEV
JINR-BLTP, Dubna
GDR-PH-QCD,Orsay, October 8, 2013
October 8, 2013
Eduard A. KURAEV

2. STATEMENT LOWEST order RC to Born ep-> ep amplitude including:
Virtual corrections
Real photon emission
vanish for both electron and proton blobs
October 8, 2013
Eduard A. KURAEV

3. PROOF = 0 = Elastic = Inelastic Cutkosky cutting rule
Let us consider s-channel discontinuity of one-loop forward scattering amplitude, which is related to the cross section through optical theorem
= 0 =
Elastic
Inelastic =
Cutkosky cutting rule
October 8, 2013
Eduard A. KURAEV

4. Analytical properties of Compton amplitude
described by planar Feynman diagrams
dispersion properties of planar amplitudes =>
ABSENCE of LEFT CUT in complex s1 plane s1 a
e e+g e+2g s1
Elastic form factors and inelastic channels
are not independent  SUM RULES
October 8, 2013
Eduard A. KURAEV

5. Analytical properties of Compton amplitude
Neglect left contribution and close contour on the right side (10% accuracy):
Cancellation of strong interaction effects in FFs and inelastic channels!
Cancellation proved exactly in QED: the L2 * -contribution to FFs is cancelled by soft photon emission
October 8, 2013
Eduard A. KURAEV

6. Analytical properties of Compton amplitude
Similar arguments were used to obtain the proton bloc
Let us consider the derivative for k2=0
-26,0/M2
+25,0/M2
Experiment
Full compensation taking into account next order of PT
(left cuts appear)
October 8, 2013
Eduard A. KURAEV

7. Charge asymmetry
October 8, 2013
Eduard A. KURAEV

8. Charge asymmetry
Arises from contribution of intermediate proton state: interference of Born and imaginary part of box amplitude
Contribution of p and N intermediate state ( D, N* resonances) have opposite signs and one order smaller magnitude .
October 8, 2013
Eduard A. KURAEV

9. 1) Soft photon emission: experimental cuts
2) Calorimeter set-up
Emission of hard photon only along the scattered electron
October 8, 2013
Eduard A. KURAEV

10. 3) Measuring the recoil proton
No restriction on photon emission
October 8, 2013
Eduard A. KURAEV

11. Deep virtual Compton Scattering
Approximation of proton as heavy lepton
Low theorem
October 8, 2013
Eduard A. KURAEV