The Kinoshita–Lee–Nauenberg theorem or KLN theorem states that perturbatively the standard model as a whole is infrared (IR) finite. That is, the infrared divergences coming from loop integrals are canceled by IR divergences coming from phase space integrals. It was introduced independently by and .
An analogous result for quantum electrodynamics alone is known as Bloch–Nordsieck theorem.
Ultraviolet divergences in perturbative quantum field theory are dealt with in renormalization.