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.(adsbygoogle = window.adsbygoogle || []).push({});

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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?

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# A Effective field theories and UV completion

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