Effective Field Theories

Abstract

In describing a physical system, one can normally focus on the degrees of freedom that are relevant at the distance scales under consideration. For example, although it is well known that quantum mechanics is a more fundamental theory than classical mechanics, it would be difficult to describe the earth’s motion around the sun by use of quantum mechanics. The state would correspond to a complicated superposition of energy eigenstates approximating the classical motion. Clearly, classical mechanics is the correct “effective theory”.