Effective field theories and UV completion

[spaghetti3451]

In QCD, there are quarks at high energies, and pions are composite degrees of freedom that appear at low energy where the quarks are strongly coupled. The pion Lagrangian is non-renormalizable; it breaks down at the QCD scale and must be replaced by the full UV-complete theory of QCD.

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Are all effective field theories non-renormalizable quantum field theories which can nonetheless be used to make physical predictions at some energy scales because all but a small number of terms in the Lagrangian are suppressed at these energy scales?

Is the UV completion of an effective field theory a completely new quantum field theory? For example, is the lagrangian of QCD completely different in character than the pion Lagrangian, but reduces to the pion lagrangian at low energies?

 

[king vitamin]

You can write down a renormalizable effective field theory - for example, the Standard Model is usually interpreted as an effective field theory. But in principle, extra non-renormalizable terms should be there, and they are simply suppressed at low energies. This is why some theorists propose looking for effects of non-renormalizable perturbations of the Standard Model at the LHC.

The QCD lagrangian should "reduce" to the pion lagrangian at low energies. But of course, this can't be done analytically because QCD is strongly coupled in that limit.