Faddeev-Kulish Approach

The Faddeev-Kulish approach addresses infrared problems in quantum field theories involving massless particles like photons. In standard calculations, interactions with low-energy ("soft") photons lead to divergences, making certain probabilities ill-defined. The Faddeev-Kulish method constructs "dressed" states that incorporate these soft photons into the particle’s description from the start, effectively including their influence. This approach ensures that calculations yield finite, physically meaningful results, accurately describing particles as always accompanied by their surrounding cloud of low-energy radiation—thus resolving the infrared divergence issue in a consistent, gauge-invariant manner.