Editing Effective field theory (section)

==Renormalization group==
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 [[symmetry|symmetries]]. If there is a single energy scale <math>M</math> in the ''microscopic'' theory, then the effective field theory can be seen as an expansion in <math>1/M</math>. The construction of an effective field theory accurate to some power of <math>1/M</math> requires a new set of free parameters at each order of the expansion in <math>1/M</math>. This technique is useful for [[scattering]] or other processes where the maximum momentum scale <math>\mathbf k</math> satisfies the condition <math>|\mathbf{k}|/M\ll 1</math>. Since effective field theories are not valid at small length scales, they need not be [[Renormalization#Renormalizability|renormalizable]]. Indeed, the ever expanding number of parameters at each order in <math>1/M</math> 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).