meopemuk
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Dickfore said:So, then, you have not proven relativistic covariance exactly, have you?
This is correct. The whole approach in Appendix O is perturbative and expansion in powers of 1/c^2 was used. Only low-order terms were retained in the proof.
However, there is a good reason to believe that relativistic invariance will be valid in higher orders as well. The traditional field-based QED is relativistically invariant (see Appendix N). The dressed particle approach is obtained from QED by means of a unitary dressing transformation, which preserves Poincare commutators (see subsection 10.2.8). Therefore, the full interaction potential between dressed charged particles must be relativistically invariant as well. Unfortunately, this full non-perturbative potential is not known yet and explicit proof of its invariance is not possible.
Eugene.