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EDIT: If all field theories, irrespective of whether it is renormizable or not, are regarded as effective field theories. The question is addressed here but there is still a confusion. I was told that gauge symmetries must be broken spontaneously because that saves the renormalizability of the theory. Does it not mean that one still prefers a renormalizable theory? If renormalizability is not a severe problem then why can't symmetries break explicitly by explicit symmetry breaking terms?

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    $\begingroup$ I would say that's just the old approach from the time when the effective field theory point of view was not known. People used to think that renormalizable theories were the only valid ones because they didn't understand non-renormalizable ones yet. $\endgroup$ – coconut Dec 28 '16 at 10:08
  • $\begingroup$ @coconut I learnt that gauge symmetries in gauge theories must be broken spontaneously because that saves the renormalizability of the theory. Does it not mean that one still prefers a renormalizable theory? If renormalizability is not a severe problem then why can't symmetries break explicitly by explicit symmetry breaking terms? $\endgroup$ – SRS Dec 28 '16 at 10:13
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    $\begingroup$ Even a non-renormalizable theory looks like a renormalizable one in the IR, because irrelevant operators become negligible at low energies. That might be a good reason to look for renormalizable theories first, as they will be at least a low energy approximation. $\endgroup$ – coconut Dec 28 '16 at 10:27
  • $\begingroup$ Could you explain how this question is different from this earlier question of yours? $\endgroup$ – ACuriousMind Dec 28 '16 at 13:28
  • $\begingroup$ @ACuriousMind I had something else at the back of my mind as I pointed out in the comment to coconut. I'll change the question. $\endgroup$ – SRS Dec 28 '16 at 14:42
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Renormalisable theories are not preferred more than non-renormalisable theories. We use the former because non-renormalisable interactions are irrelevant, and when we build a model, we always omit those variables that are insignificant to the fit.

Or put it another way: Nature is not a QFT. There are not "correct" vs "incorrect" interactions. We use interactions only if they serve us to correctly model the observed phenomena; and non-renormalisable interactions are (in general) useless for our model: they have no measurable effect in the range of energies we perform experiments.

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