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  • $\begingroup$ Thanks for the answer. Some aspects are still rather mysterious to me, but I'd need to read more on the subject to understand it. One question: why precisely does the RG flow stop at the cut-off scale? The scale as I know it is a scale for the momentum of the field, so how does it relate to the coupling constant? $\endgroup$ Commented Mar 25, 2014 at 22:35
  • $\begingroup$ @Peter: what I mean is that when one lowers the cut-off (in a Wilsonian point of view) below the scale given by the mass, the flow stop. This is because the mass is then a high energy scale in the propagators compare to the typical momentum scale (of the order of the cut-off), and therefore the loops are suppressed. $\endgroup$ Commented Mar 25, 2014 at 23:04
  • $\begingroup$ Do we really know that QED doesn't have a UV fixed point? I think it's not clear that the Landau pole isn't an artifact of perturbation theory, or perhaps you disagree? $\endgroup$ Commented Dec 4, 2018 at 15:42
  • $\begingroup$ @JulianIngham To my understanding, this is a rather academic question, since QED is just a subpart of the standard model. It could very well be that including other irrelevant operators removes the Landau pole, but I don't know this literature enough to give a relevant answer to this question. $\endgroup$ Commented Dec 4, 2018 at 16:19
  • $\begingroup$ Yeah exactly re standard model, it's not relevant to the real world it's totally academic. Just saying I am not sure whether QED is not not-asymptotically safe or not! $\endgroup$ Commented Dec 4, 2018 at 16:25