In
physics, an
effective field theory is a type of approximation to (or
effective theory for) an underlying physical theory, such as a
quantum field theory or a
statistical mechanics model. 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). Intuitively, one averages over the behavior of the underlying theory at shorter length scales to derive what is hoped to be a simplified model at longer length scales. Effective field theories typically work best when there is a large separation between length scale of interest and the length scale of the underlying dynamics. Effective field theories have found use in
particle physics,
statistical mechanics,
condensed matter physics,
general relativity, and
hydrodynamics. They simplify calculations, and allow treatment of
dissipation and
radiation effects .