An effective field theory includes the appropriate degrees of freedom to describe physical phenomena occurring at a chosen length scale or energy scale, while ignoring substructure and degrees of freedom at shorter distances (or, equivalently, at higher energies).
[1][2] Presently, effective field theories are discussed in the context of the renormalization group (RG) where the process of integrating out short distance degrees of freedom is made systematic.
Although this method is not sufficiently concrete to allow the actual construction of effective field theories, the gross understanding of their usefulness becomes clear through an RG analysis.
This method also lends credence to the main technique of constructing effective field theories, through the analysis of symmetries.
This technique is useful for scattering or other processes where the maximum momentum scale
Since effective field theories are not valid at small length scales, they need not be renormalizable.
required for an effective field theory means that they are generally not renormalizable in the same sense as quantum electrodynamics which requires only the renormalization of two parameters (the fine structure constant and the electron mass).
In this more fundamental theory, the interactions are mediated by a flavour-changing gauge boson, the W±.
The immense success of the Fermi theory was because the W particle has mass of about 80 GeV, whereas the early experiments were all done at an energy scale of less than 10 MeV.
This theory has had remarkable success in describing and predicting the results of experiments on superconductivity.
Effective field theories have also been used to simplify problems in general relativity, in particular in calculating the gravitational wave signature of inspiralling finite-sized objects.
[3] The most common EFT in GR is non-relativistic general relativity (NRGR),[4][5][6] which is similar to the post-Newtonian expansion.