 Bethe–Salpeter equation

The Bethe–Salpeter equation (BSE) is an important integral equation in quantum field theory and many-body physics that describes the behavior of two-particle bound states, particularly within the context of quantum electrodynamics (QED) and other field theories. It provides a framework for studying the interactions of pairs of particles, such as electrons and positrons, and can be applied to various systems including excitons in semiconductors, mesons in particle physics, and more.